I get a certain question every so often, and it’s one of the most difficult questions any cosmologist faces. Today, I try to tackle it. It goes something like this:

If the Universe is 13.7 billion years old, and nothing can go faster than the speed of light, how is it that we see things that are 46.5 billion light years away?

First off — and I want to clarify this — everything in this question is legit.

1.) The Universe is 13.7 billion years old. There are small errors there — no one would be surprised if it was 13.5 billion or 14.0 billion years old — but it’s definitely not 12 billion years or younger and definitely not 16 billion years or older.

2.) Nothing can move faster than the speed of light. If you’ve got a mass, whether you’re a galaxy, a spaceship, a bullet or a neutrino, you’re going to go slower than the speed of light. And if you don’t have a mass, you’re going to move exactly at the speed of light. No exceptions.

3.) The farthest things in the Universe — the things that emitted their light 13.7 billion years ago — are 46.5 billion light years away from us now.

So how did this happen? Two things, one simple and one not-so-simple. The simple thing is that the Universe has been expanding this entire time. Imagine you’ve got an ant on a deflated balloon, and the ant moves at a rate of 1 cm/second. When the balloon is totally deflated, the ant is only 2 cm away from the top of the balloon, her destination. But as she starts walking towards the top, something inflates the balloon. As she walks towards the top, she notices that the balloon around her is expanding.

How does this expansion work? Well, this is the not-so-simple part. Expansion isn’t a velocity. It’s a velocity-per-unit-distance. Let’s say that it’s 0.4 cm/second per centimeter. This means that if the ant is 1 cm away from something, it expands away from her at 0.4 cm/second. The top of the balloon, initially, since it’s 2 cm away, expands away at 0.8 cm/second. And something that’s 15 cm away would be expanding away at 6 cm/second.

So if I run through the math of this ant walking at 1 cm/second to a point 2 cm away on this expanding balloon, it doesn’t take 2 seconds to get there. In fact — doing the math correctly — it takes just a shade over 3 seconds for the ant to reach her destination. Moreover, the balloon has continued to expand, so when she looks back at her starting point, do you know how far away it is? Over 6 cm away! When she looks back at her starting point, not only is it more than three times as far away as it was when she started, but the entire balloon is bigger than it was before.

And that’s what our Universe is doing: expanding while the light is traveling towards us from distant sources. There is, of course, one more caveat in our Universe. The expansion rate is mind-bogglingly slow, 72 kilometers per second per Megaparsec. In the ant’s terms, that’s 2.3 x 10^-18 cm / second / cm. It’s just that our Universe is so big that as you get far enough away — just under 13 billion light years — the expansion rate eventually becomes greater than the speed of light.

But this is okay. It’s only that space (i.e., the balloon) is expanding; there’s no matter that’s moving. So, in principle, space can expand as quickly as it wants, even faster than the speed of light, because there’s nothing moving. And that’s why, even though the Universe is only 13.7 billion years old, we can see things that are 46.5 billion light years away.

Any questions?

Comments

  1. #1 Greg Laden
    July 31, 2009

    So, young Woody Allen’s bedroom IS getting larger over time and therefore he does not have to clean it.

    Oh, can massless particles stay still at all?

  2. #2 Ethan Siegel
    July 31, 2009

    Greg, the expansion only works for objects that aren’t bound. Woody Allen’s bedroom (and many of our waists) may be expanding, but we can’t blame that on the Universe.

    Massless particles can only stay still if you have a medium where the speed of light in that medium is infinitesimally small. Theoretically possible, but not yet discovered.

  3. #3 sean hogge
    July 31, 2009

    The hard part to wrap my head around was that we can only see objects less than 13.7 billion years old (time), but that might have “traveled” more than 13.7 billion light-years (distance) even though we all started extremely close together. Obviously that is partly because time and space are so intertwined, yet time and space appear to function on wholly distinct levels.

    Brian Greene explains some portion of it as a limitation of movement. You can either move through time or through space, but the more you move through one, the less you can move through the other. Mathematically, does this mean that a massless particle doesn’t experience time? Or is that past the point in which our maths cease working?

  4. #4 Brando
    July 31, 2009

    I’m a little confused. I was under the assumption that the visible horizon of the universe is about 13.7 billion years but the 46.5 billion number is the physical size. We can’t actually see anything beyond 13 billion light years, right?

  5. #5 Comrade PhysioProf
    July 31, 2009

    Dude, that shit hurts my brain. I prefer to think of it like this:

    (1) The universe is fucking huge, and getting even fucking huger.

    (2) The universe is fucking old, and getting even fucking older.

  6. #6 John Swindle
    July 31, 2009

    I’d say that’s a pretty good answer to a darn good question… because I seem to understand what you said.
    Greg Laden said:
    “…can massless particles stay still at all?” It is said that nothing is able to leave black holes. So are massless particles doing anything in there? Just standing around? Motionless? Wriggling at light speed?

    I am ill-equiped to deal with such thoughts, and unable to stop thinking them. Ouch.

  7. #7 Roadtripper
    July 31, 2009

    That’s just about the most straightforward explanation for this concept I’ve seen, but my head still hurts thinking about it. Then again, I had a migraine when I started reading this post, anyways.

    One more question: does inflation theory have anything to do with this?

    Rt

  8. #8 jdhuey
    July 31, 2009

    Thanks for the very cogent response. So, am I correct in assuming that the famous red-shift is due to the ‘stretching’ caused by the 13.7 billion year journey covering the 46.5 billion light-year distance?

    Related to the geometry question: does the density of galaxies drop off as the distance away increases?

  9. #9 Greg Laden
    July 31, 2009

    Actually, what I’ve heard is that Teh Expanshun as it were affects all things, but bunches of matter have other forces that counter act it at scales of Woody Allen’s bedroom.

    However, this is not entirely clear to em. So I get that adhesion keeps the fly the same distance from the ceiling as the universe expands, and so on, but are the subatomic forces that keep atoms the same relative size unaffected? Is the volume of space within a block of solid metal the same before and after expansion? From what you are saying, it sounds like it is.

    Also, is expansion a force?

  10. #10 hyphenate
    July 31, 2009

    This is so simply stated that I can’t help but want to make it even more complex, simply on sheer contrariness. So here are a couple of questions:

    1) Aren’t tachyons supposed to move faster than the speed of light? Or are they still only considered hypothetical?

    2) Is there any evidence that an anti-matter universe exists, expanding at the same rate of our own universe? If it is also theoretical that matter and anti-matter could destroy each other, would it also mean that there be some requisite “neutral zone” between them? And if such, what would the size of such a zone have to be?

    3) If we use string theory (m-theory) to hypothesize the existence of an infinite number of parallel dimensions, might we also conclude that some of these other dimensions might be older/larger than our own dimension?

    Yeah–I know; I read too much science fiction and watch too many specials on the Discovery channel. ;-)

  11. It is said that nothing is able to leave black holes. So are massless particles doing anything in there?

    As I understand it, they are moving at the speed of light along geodesics just like they do outside the black hole. The geodesics all curve toward the center eventually, though.

  12. #12 Pierce R. Butler
    July 31, 2009

    Given that the existence (but next to nothing about the features) of ~90% of the “known” cosmos has only been discovered during my lifetime so far, please allow me a grain or two of salt concerning present-day statements about the absolute limits of that universe thingy out there.

  13. #13 Nick
    July 31, 2009

    If the universe has a beginning, does that imply that the ‘whole’ universe (not just the ‘observable’ is not infinite in size. If the universe is infinite in size does this make inflation obsolete? And is a infinite universe automatically a static universe?

    Not entirely related to the post, but something that kept hanging in my mind from one of your earlier posts a few weeks ago :)

  14. #14 Pierce R. Butler
    July 31, 2009

    Oh, and the question(s) I’d meant to ask:

    If what Einstein labeled the cosmological constant is a mere 72 meters per second per kiloparsec (funny, my unit-converter desktop widget doesn’t do parsecs, or even lightyears – time for a system upgrade!), how much space is even theoretically in reach?

    Just as there is some calculable radius beyond which an ant with a set walking speed can never reach on an endlessly expanding balloon, there must be some sizable fraction of visible space which even a hypothetical Leonora Christine scooting along at .999…c could not approach (as it would, eventually, in a static universe, if the crew brought along enough brown rice & vitamin E to make maximum use of their time dilation).

    We might hope for our 999…x grandkids to explore the local galactic cluster, but how far out is the locus where the expansion rate = c? Is there a convenient spacemark?

  15. #15 David Horton
    July 31, 2009

    Sorry to burst your balloon, but if there is an ant walking on it, it is, except in very unusual circumstances, a MALE.

    And there are some good questions in the thread. I thought you were saying that the universe is currently 46.5 billion light-years across, but we can only see things 13 billion light years away. If that is not what you are saying (“we can see things that are 46.5 billion light years away”) I have a serious misunderstanding of space-time, the universe, and everything.

  16. #16 Jo
    July 31, 2009

    @#15: David, I’m assuming you’re referring to the likelihood that the referenced ant is a worker ant. In which case, it IS a female. Workers ants are females. Not males.

  17. #17 gerwood
    July 31, 2009

    what is outside the universe for it to expand into? If time stopped, how could you know? How can time stop because if it did stop you would have to ask for how long thereby inserting time back in.

  18. #18 MichelP
    July 31, 2009

    @David: The farthest possible light source, when it started its travel towards us 13B years ago, did so in a ‘smaller’ universe. 13B years later, when it reaches us, the universe has expanded, and that particular light source is now calculated to be 46B light years away from us. Yes?

  19. #19 NewEnglandBob
    July 31, 2009

    13.7 billion years ago, the entire universe was all in one place, so why would light from then just get to us now? The distance from everywhere was short so it would not take light long to get ‘here’.

    @17 – there may not be any ‘outside’ the universe. It may just wrap around on itself. Time could speed up or slow down and you would not be able to sense it – see info on relativity.

  20. #20 Pierce R. Butler
    July 31, 2009

    Oops, on re-reading the post I see my question @ # 14 was answered already:

    … just under 13 billion light years — the expansion rate eventually becomes greater than the speed of light.

    That this magic radius should be a number so close to the estimated age of everything I rather hope is coincidental, or I’ll have to take up some serious anthropic-principle crackpottery. Either way, I’m still hoping there’s a handy supercluster edge or the like to indicate the boundaries of our invisible plate glass window – or something striking and famous on the other side, as a handy metaphor for the ever-unreachable.

  21. #21 Ethan Siegel
    July 31, 2009

    Bob, you know how it took the ant more than 2 seconds (at 1 cm/sec) to go 2 cm? Yeah… it takes light 13.7 billion years to go the tiny distance that the Universe was spread apart all the way back at the beginning.

    Mind-numbing, but true.

    It also looks like there are some things I need to clarify, including just what I mean by “position, motion and moving”, since those terms mean something very different in cosmology than in our common usage.

  22. #23 Pierce R. Butler
    July 31, 2009

    It also looks like there are some things I need to clarify…

    Among those might be your choice of units – why “72 kilometers per second per Megaparsec” instead of 72 meters/sec/kiloparsec or “2.3 x 10^-18 cm / second / cm” instead of 2.3 x 10^-16 m/second/m, except for the sheer astronomical joy of packing on a few more orders of magnitude?

  23. #24 David Horton
    July 31, 2009

    #16 D’oh, you are right. Old age creeps up on one, and then, undetected, whacks you over the head with a large rock.

  24. #25 David Horton
    July 31, 2009

    #18 doesn’t that imply that all the light from all the bit between 13.7 and 46.5 billion light-years away from would arrive on Earth at the same time? Or do I have ants in my head?

  25. #26 Eric
    July 31, 2009

    I get what you’re saying…it’s the space that’s expanding, and it can do so faster than the speed of light. However, from what I understand (and I could be wrong), gravity waves, which are only ripples in space-time, move at the speed of light. Why are they limited and the expansion is not? Is the universe accelerating outwards? If it is, what could make it do so?

  26. Why are they limited and the expansion is not?

    Because the gravity waves are moving through space. They are a form of energy moving from one place to another, just like a radio wave. It’s motion through space that is limited by the speed of light, not the expansion of space itself.

  27. #28 Brian
    July 31, 2009

    Expansion isn’t a velocity. It’s a velocity-per-unit-distance.

    The expansion rate is mind-bogglingly slow, 72 kilometers per second per Megaparsec. In the ant’s terms, that’s 2.3 x 10^-18 cm / second / cm.

    Or, since the distance units on top and bottom cancel out, the expansion rate can be expressed as a frequency, namely 2.3 x 10^-18 Hertz!

    More seriously, though, I just realized that 2.3 x 10^-18 Hertz is approximately equal to 1 / (13.7 billion years) — whoa. I don’t entirely see why that works out, but I assume that that’s not a coincidence. Ethan?

  28. #29 Ethan Siegel
    July 31, 2009

    It is kind of a coincidence, Brian. It depends on what’s in your Universe.

    For a Universe that was 100% radiation, a 13.7 billion year old Universe would have an expansion frequency of (1/2) / (13.7 billion years).

    For a Universe that was 100% matter, a 13.7 billion year old Universe would have an expansion frequency of (2/3) / (13.7 billion years).

    For a Universe that was 100% dark energy, a 13.7 billion year old Universe would have an expansion frequency of (infinity) / (13.7 billion years).

    And for our Universe, of about 27% matter, 73% dark energy and a negligible amount of radiation, it works out to just about 1 / 13.7 billion years. It’s neat.

  29. #30 JD
    July 31, 2009
    Sorry to burst your balloon, but if there is an ant walking on it, it is, except in very unusual circumstances, a MALE.

    @#15: David, I’m assuming you’re referring to the likelihood that the referenced ant is a worker ant. In which case, it IS a female. Workers ants are females. Not males.

    Most definitely. I was impressed Ethan included that little detail in the article. Nice. Haplodiploidy FTW.

  30. #31 Boronx
    July 31, 2009

    But isn’t the expansion frequency increasing? Does that mean the proportion of dark energy is increasing?

    I wonder, is it just about 1 or is it exactly 1/ApparantAgeOfUniverse.

  31. #32 Anton Mates
    August 1, 2009

    David #24,

    If it’s any consolation, I assumed you meant that the ant was a drone, because it wouldn’t be on top of a balloon in the first place unless it could fly…

  32. #33 Alex
    August 1, 2009

    Two questions:

    1) The universe could easily have expanded fast enough so that there are still things at the outer part of the universe whose light has never reached us, right? We therefore can have no idea how big the universe really is, but only a lower limit.

    2) Do any “contradictions” show up based on the fact that when we see something so many billions of light years away it is actually the billions-years-old version of the matter? This doesn’t happen in daily life because as nothing can move faster than the speed of light, we don’t get any contradictions in what we see. But with things moving outward and expanding faster than the speed of light, it seems like what we see could create some paradoxes.

  33. #34 eff
    August 1, 2009

    Can I ask some more ripe amateur questions?

    1. So if the oldest things in the universe are now 46.5 billion light years away, then why doesn’t this blog mention the number 93 billion light years via d=2r? Or are we not at the center of the universe? Is one side of the universe closer to us?

    2. Is the same thing that’s beyond the edge of the universe the same thing that was outside of the singularity in the moment before the big bang?

    3. Is it annoying to cosmologists when in science documentaries the big bang is animated as a really humongous explosion in space as seen from the outside? Is there any chance that the singularity existed as a point inside a pre-existing space/vacuum?

  34. #35 Change
    August 1, 2009

    This is interesting. I never thought about it before.

    Now, I plugged these into a differential equation to see if I arrive at 46.5 billion light years. I’m arriving at 8.63 billion light years. I’m probably missing something.

  35. #36 João Carlos
    August 1, 2009

    [To everybody: I'm the guy who commited the translation into Brazilian-Portuguese. I'd like to thank Ethan publicly]

    And back to the questions: there are two other points I would like to see explained. The first one is the question gerwood asked: “what is outside the universe for it to expand into?” And the second is about biting one’s own tail when it comes to define “distance” and “time”.

  36. #37 Brian
    August 1, 2009

    Thanks for the extra info, Ethan. I’ve definitely had my U.S.RDA of unexpected coolness now.

  37. #38 Bryan
    August 1, 2009

    “Massless particles can only stay still if you have a medium where the speed of light in that medium is infinitesimally small. Theoretically possible, but not yet discovered.”

    They were able to slow light down to 38 mph. They should be able to bring light to a stand still fairly soon, if they haven’t already.

    http://www.news.harvard.edu/gazette/1999/02.18/light.html

  38. #39 NewEnglandBob
    August 1, 2009

    Ethan @21:

    I am still perplexed. If the expansion is 72 kilometers per second per Megaparsec, but 13.7 billion years ago the universe was (relatively) small, then why would the expansion then have beeen faster than light when the expansion accumulates over a large distance to become faster than light. Across the small distance it should have been relatively small.

    I am not trying to argue with you, I am trying to understand.

  39. #40 Curdle1
    August 1, 2009

    Nice explanation.

  40. #41 Ethan Siegel
    August 1, 2009

    NewEnglandBob,

    The quick answer is that the expansion rate is related to the energy density of the Universe. Because the Universe was smaller in the past, it was *denser* in the past, and therefore expanded faster. 72 — the current value — is the smallest value it’s ever had.

    The long answer will need its own post. ;-)

  41. #42 Lewis Thomason
    August 1, 2009

    How do I explain this to my father-in-law who has a sixth grade education and thinks the universe is 6 thousand years old? Should I just forget it or what.

  42. #43 MarkSeid
    August 1, 2009

    I’m still troubled with a two-part question. (1) If we see something whose red shift indicates it was 13 BLY away 13 BY ago, how far away is it now? (2) How did it get to be 13 BLY away so soon after the Big Bang?

  43. #44 Sam L.
    August 1, 2009

    Lewis @42, you might want to start smaller. Like with something that’s 7 thousand years old.

  44. #45 Shadow14l
    August 1, 2009

    Expansion of the Universe (FTL)

    According to Hubble’s Law, two galaxies that are a distance D apart are moving away from each other at a speed HD, where H is Hubble’s constant. So this interpretation of Hubble’s Law implies that two galaxies separated by a distance greater than c/H must be moving away from each other faster than the speed of light. Actually, the modern viewpoint describes this situation differently: general relativity takes the galaxies as being at rest relative to one another, while the space between them is expanding. In that sense, the galaxies are not moving away from each other faster than the speed of light; they are not moving away from each other at all! This change of viewpoint is not arbitrary; rather, it’s in accord with the different but very fruitful view of the universe that general relativity provides. So the distance between two objects can be increasing faster than light because of the expansion of the universe, but this does not mean, in fact, that their relative speed is faster than light.

    As was mentioned above, in special relativity it is possible for two objects to be moving apart by speeds up to twice the speed of light as measured by an observer in a third frame of reference. In general relativity even this limit can be surpassed, but it will not then be possible to observe both objects at the same time. Again, this is not real faster than light travel; it will not help anyone to travel across the galaxy faster than light. All that is happening is that the distance between two objects is increasing faster when taken in some cosmological reference frame.

  45. #46 bigTom
    August 1, 2009

    When I think of the size of the universe I do it in the sense of #33. We can only see things that were close enough 13Byears ago that the light is just reaching us, a little further away (initially), and we are still waiting for it to meet us (at higher and higher redshift I presume). But we have several meanings of size, one is how far away we can see things from the past (that is the 13e9 LY number, -or 46e9 if we consider how far away those things are now, but anaything currently 46e9 LY away is noe incapable of ever sending a signal to us? So another question, is if I send out a signal at the speed of light, how far (in terms of todays space-time) will it get, i.e. if I see light from a galaxy say 4BY ago, can I send a beam of light that will reach it? Or will it expand out of range before my signal arrives? So I suspect the size of the universe we could get to if we could travel at c, is a lot smaller than the universe we can currently see.

    And then we have the more fundamental question, how big in total is the universe, including those parts we can never see (noting that there is much more beyond our “horizon” than within it)? I suspect we don’t know how to answer that one.

  46. #47 bk
    August 1, 2009

    that was an amazing explanation. thanks!

  47. #48 shlog
    August 2, 2009

    This is what i think: our capacity to understand the massive/tiny time & distance scales of the universe are too hard for a monkey brain to comprehend intuitively. “Seeing is believing” – and we have trouble grasping the fact that the image of an object is not the object itself.

    An experiment is everyday living:

    1. you place a fresh green apple 1 foot away, and take a polaroid photo of it, and place the photo in front of the apple. (Don’t look at the apple or the photo).

    2. throw the apple on the back of a truck as it speeds away, wait a year till it’s completely rotten in some landfill somewhere.

    3. now open your eyes- and look at the apple image.

    4. Ask yourself: “where is the apple really?”

    5. Ask yourself: “where is the image of the apple?”

    That’s what looking up at the night sky is like. Looking up at the stars is not at all like looking down at your feet. Actually, it’s a lot like looking at a photosynth image- a composite image of a region of space, but with each photograph representing a different time.

    shlog
    http://shlogblog.blogspot.com/

  48. #49 opony szczecin
    August 2, 2009

    Yes, you are right. Good job !

  49. #50 private
    August 2, 2009

    Still doesn’t answer the question of reference frame for measuring space-time to my satisfaction. Where do you stand when you measure the age or size of the universe?

    A related question would be, how can we say something is happening simultaneously here and on a star 40 billion light years away? There is no reference frame in this universe to determine the answer. While your intuition might imagine standing outside and seeing events happening simultaneously, in fact space IS time. You measuring device must exist somewhere in space-time.

    If you think, well, the observer can be half way between the two stars, then consider determining simultaneity between 100 dispersed stars. No observer can be equidistant between all of them.

  50. #51 Edward L. Scott
    August 2, 2009

    Very interesting article and discussion. Just as an observation, no one has mentioned that the universe was opaque until several hundred thousand years after the big bang. Any observable radiation (light or otherwise) has to have been radiated after the universe went transparent. Also, no one has mentioned that most physicists (from what I’ve read) now adhere to the concept of hyper-expansion that seemingly indicates that the rate of inflation is not constant across our 13.7 BYs of existence.

    Although I am not a physicist nor a cosmologist, I have pondered what the hell is going on since I was young just like most of us. I’d like to address the question, “what is outside the universe for it to expand into?” postulated above.

    I have come to my own conclusion that there are multiple universes, each one a derivative of an earlier universe. New universes “foam” (for lack of a better word) out of earlier universes in an ongoing process. Each is a distinct space-time-gravimatric (my term) envelope separated by the quantum curtain (the set of weird events observed at the scale of the infinitesimally small). The process is analogous in my theory to the way matter accretes in our universe into suns that ultimately collapse via novas/supernovas into denser objects (neutron stars or black holes), that then will logically continue to capture any additional available matter due to to their extraordinary mass. Unlike Hawking who sees black holes magically evaporating, I foresee that a black hole could continue growing in mass to a point where, analogous to a nova/super-nova, it could no longer support its mass within the context of our universe, and collapse catastrophically through a singular quantum event (i.e. a big bang event), exit our universe, and come out the other side as a discrete new space-time-gravimatric universe similar to our own, but now outside the envelope of our own space-time-gravimatric universe. Whether any given black hole experiences this is dependent on collecting enough matter to reach the threshold of necessary mass. The mass involved in the event would exit our universe and form a new one, taking the gravity associated with it into the new space-time bubble. The loss of gravity from our universe would contribute toward an accelerated expansion (as widely theorized to occur) since that which holds back universal expansion is the gravity of our universal mass. Ultimately, the answer to the question posed above is, “It is the quantum matrix within which all the space-time-gravimatric envelopes independently exist.”

    OK, so I’m crazy to have my own theory – prove me wrong.

  51. #52 eddie
    August 2, 2009

    I’d like to contribute a few clarifications to comments upthread.
    Someone mentioned the 72km s-1 Mpc-1 as being the Cosmological constant. It is Hubble’s constant. Further, it is the current value of a measure that’s constant over space at each time, but which changes with time. The Cosmological constant relates to how the Hubble constant varies.
    In another comment was asked “Does that mean that photons don’t travel through time?” No. Photons move along what are called ‘null geodesics’. These are sets of events (world lines) for which the invariant interval is zero. The invariant interval is the root of the difference between the squares of the time and space intervals between events. It may be a real number, if the events are close enough to be causally connected, and imaginary if they are not.

  52. #53 Fjordo
    August 2, 2009

    There is something Newtonianly incorrect about this. It seems to imply that because of the mechanics of expansion, that two objects can move apart from each other at greater than the speed of light. In fact, the very statement that objects are farther apart from each other than 13.7 billion years implies that in some way we have had two objects move apart from each other at a rate greater than the speed of light. However, special relativity shows that this is impossible: any two objects can only depart from each other at a maximum rate of the speed of light. I don’t feel you’ve addressed this well, because you have used Newtonian mechanics to explain an issue with relativity.

  53. #54 Darren
    August 2, 2009

    If space has been expanding then why not the objects (matter) occupying that space?

    We know that light waves lengthened as the space the occupied expanded. Have any other waves lengthened? Elementary particles are both particles and waves so why has the ‘wave’ aspect of particles not increased?

    Thanks for the interesting article.

  54. #55 Arthur Ice
    August 2, 2009

    Wouldn’t it be possible for a particle to travel _faster_ then light if it some how had negative mass? (yes i know, it may be silly physically but come on the math works doesn’t it?), I’m pretty sure this would also mean it traveled in the reverse direction in time but i haven’t played with the relativity equations enough yet to be sure.

  55. #56 Crux Australis
    August 2, 2009

    Man, I’ve been out of the loop for too long. What’s 46.5 billion light years away?

  56. #57 José
    August 2, 2009

    I’ll try a few of the unanswered questions, if anyone’s still reading. First though, I want to say that it’s important to remember that it’s not really possible to really visualize how the expansion of the universe works. You can’t do it, and the smartest man alive can’t do it. God even throws up his hands. Some ways of conceptualizing it are better at describing different aspects than others, but all are limited in some way.

    @Alex
    The universe could easily have expanded fast enough so that there are still things at the outer part of the universe whose light has never reached us, right?

    Yes. And there is light that will never reach us.

    We therefore can have no idea how big the universe really is, but only a lower limit.

    Correct.

    Do any “contradictions” show up based on the fact that when we see something so many billions of light years away it is actually the billions-years-old version of the matter… with things moving outward and expanding faster than the speed of light, it seems like what we see could create some paradoxes

    I think I understand what you’re getting at, and the answer is no. Matter has never been moving away from us faster than the speed of light through space, so no laws of physics are being broken which would create paradoxes.

    @eff
    So if the oldest things in the universe are now 46.5 billion light years away, then why doesn’t this blog mention the number 93 billion light years via d=2r? Or are we not at the center of the universe?

    There is no center to the universe. If you look at the balloon analogy, you can’t pick any one point on the surface of the balloon and call it the center.

    @João Carlos
    what is outside the universe for it to expand into?

    This is another thing that’s difficult to conceptualize. If you go back to the balloon analogy again, you might answer that the balloon is expanding into air, but you’ve just broken the analogy. For the analogy to work, you have to accept that the surface of the balloon is all there is. If you were living on the balloon, you couldn’t even point to anything off the balloon. Now, scale the analogy up to the three dimensional world we live in and try to point to a direction where space doesn’t exist. You can’t. The question stops making sense.

  57. #58 jdhuey
    August 3, 2009

    Let me paint a picture here using the ant on the balloon analogy and please tell me if I have made the correct deductions. Assume that the ant has a telescope that he uses to peer at the galaxies far far away. Since this is a two dimensional analog what he sees is bright line segment that will subtend a certain angle depending on how far away and how big the galaxy is. Now with a static balloon, I don’t see any problems: the light from one tip of the galaxy heads toward the ant at the same time that light from the other tip of the
    galaxy heads toward the ant. The light meets at the ant forming a triangle. The angle at the apex of the triangle is determined by the distance away and by the size of the galaxy
    (ignore the curvature aspect of the balloon). But now if we allow the balloon to expand, the space between the galaxy and the ant expands, spreading the two beams of light apart
    - the affect would be that by the time the light reached the ant, the galaxy would appear to be bigger than it would have in a static balloon. This same spreading of the light
    should also make the distances between distant galaxies appear larger – that is the population of distant galaxies should appear to be less dense. (Note that this distortion occurs just because of the effect of the expansion on the light beams and has is not affected by the fact that the expansion does not change the size of the galaxy.)

    The picture I painted here seems to me to be logically required by an expanding universe but I can’t ever recall reading about this size distortion. So, do I have something terribly wrong? Or, is this size distortion just something that astromoners keep to themselves?

  58. #59 planck
    August 3, 2009

    It’s crazy to think about what it would have been like to have been born early enough to see the big bang and then, like, remember all the stuff that happens until now and we didn’t even realize this stuff until a few years ago. Not only is the universe expanding, but so are our minds. I bet some day we can think at the speed of light, and poof… we’re there.

  59. #60 Nick
    August 3, 2009

    Isn’t it that space doesnt expand into anyting but rather it is space itselfs that expands (stretches?)

  60. #61 boburob
    August 3, 2009

    Actually in response to no.2:

    http://www.newscientist.com/article/dn16796-fasterthanlight-tachyons-might-be-impossible-after-all.html

    Einstein theory of relativity is not guaranteed to be correct.

  61. #62 Bjoern
    August 3, 2009

    @jdhuey:
    What you are talking about is the so-called “angular size distance”; it is described e. g. here: http://www.astro.ucla.edu/~wright/cosmo_02.htm

    And yes, this is essentially “something that astromoners keep to themselves”; I’ve never seen this discussed anywhere in popular-science accounts of the Big Bang theory…

  62. #63 Bjoern
    August 3, 2009

    @Pierce R. Butler:
    The reason for the unit “kilometers per second per Megaparsec” is simply convenience. Galaxies typically have speeds on the order of a few hundred or thousands of kilometers per second, and distances on the order of a few Mega- to a few Gigaparsecs. Hence the Hubble constant is usually expressed in these units, since one usually talks about the relation between the speeds and the distances of galaxies.

    But following up with what Brian wrote, for visualizing the expansion of the universe, it is much more convenient to cancel the distance units out and think of the Hubble constant as 1/(13.7 billion years), or, equivalently, as about 7 percent per billion years. In this way, you avoid the problem which Ethan mentioned (“Expansion isn’t a velocity. It’s a velocity-per-unit-distance.”) and see that the Hubble constant simply tells you by which factor the universe expands per billion years.

  63. #64 Mu
    August 3, 2009

    So, how does that all influence the redshift? Does an object 13 by old and 40 bly away from us have a different redshift than a 13 by old object 13 bly away?

  64. #65 Bill R.
    August 3, 2009

    “The Universe is 13.7 billion years old. There are small errors there — no one would be surprised if it was 13.5 billion or 14.0 billion years old — but it’s definitely not 12 billion years or younger and definitely not 16 billion years or older. ”

    Expansion or not, the age of the universe can never be proven. Some scientists believe it to be infinite. So, I fail to see the point of that statement.

    Sorry if I come across harsh. But I grow tired of the circulation of information based on scientific theories that have yet to be proven.

  65. #66 jdhuey
    August 3, 2009

    @Bjoern

    Thanks for the link and thanks for confirming the lack of discussion of this topic in the realm of popular science topics. It is very gratifying to have ones intuitions validated by a more rigorous analysis.

  66. #67 tom
    August 3, 2009

    But isn’t all of this too confusing for me to understand? Shouldn’t I not think so hard? If I wanted to think I wouldn’t be pressing the stumble button.

  67. #68 bomvom.com
    August 3, 2009

    Great article, Science Be Praised! Read more science like this at BomVom.com

  68. #69 Alex
    August 3, 2009

    @Jose #57: Thanks for clearing that up!

  69. #70 Ethan Siegel
    August 3, 2009

    Having trouble with distances, positions, and motion in the expanding Universe?

    Yeah, you and everyone else. I’ve written a little follow-up to help you try and wrap your head around it:

    http://scienceblogs.com/startswithabang/2009/08/distances_position_and_motion.php

  70. #71 Flemming Jacobsen
    August 3, 2009

    I’m an M.Sc.EE., so bear with me …

    Your ’2.)’ says that light has no mass.
    I was under the impression that gravitational lenses were created when heavy objects bend the path of light using gravity.
    What am i missing?

  71. #72 D. Marshall
    August 3, 2009

    So what is on the ‘other side’ of nothingness? If our definition of the universe is stuff from the big-bang, then what is on the other side of the stuff or nothingness? If the big-bang reaches a stopping point (assuming contraction theory), then like a stop sign what is on the other side of the street?

    So if we were in a ship and ‘ran the stop sign’ while the rest of the universe contracts backward, is there an end? Your ant-on-a-balloon example is good. But put the balloon and ant inside a football stadium and you see what I mean.

    Just thoughts . . . don’t let it get in way of your good stuff.

  72. #73 jdhuey
    August 3, 2009

    @Flemming

    As I understand it there are two things to keep in mind: rest mass and thinking of gravity as a bending of space-time. The photon has a rest mass of zero (that is from the perspective of the photon it is indeed massless) but WE forever see the photon as moving (with the speed c when in a vacuum). So, when we look at a photon it carries with it a certain amount of energy and – because of E=mc^2 – momentum and mass. (It was based on this mass that Einstein predicted that light from a star would be bent the mass of the Sun but he predicted an amount of deflection based on just Newtonian Gravity that turned out to be much less than the actual deflection.)

    When Einstein developed his General Theory of Relativity and deduced that gravity was best thought of as mass causing space-time to bend, he revised his calculations of the deflection and came up with a revised number that matched what was actually observed.

  73. #74 vince p
    August 3, 2009

    First- the center of the universe is wherever you happen to be. If you go in any direction, any speed you choose, the universe will put you in the center of it. Second- we are all centers of our own universes, separated on our scale by the speed of light. Yes, the center of the universe of the person sitting next to me is 2′ (or the time it takes light to travel that distance) from mine. 2′ further than my universe in his direction and 2′ further than his in my direction. Third- there is discussion of the idea that time itself is slowing down, though we would never know it. This has implications concerning dark matter and inflation. My head hurts now.

  74. #75 Bjoern
    August 4, 2009

    @Mu:
    “So, how does that all influence the redshift? Does an object 13 by old and 40 bly away from us have a different redshift than a 13 by old object 13 bly away?”

    We can’t see the light of objects which are 13 by old now (and hence we can’t sensibly talk about its redshift); that light will reach us only in the future. The light which we receive now from these objects left them when they were younger than 13 by.

    So, please try to rephrase your question; I’m not sure what you wanted to know exactly.

  75. #76 Bj
    August 4, 2009

    @Bill R.:
    “Expansion or not, the age of the universe can never be proven.”

    No theory in science can ever be “proven”. However, we have very good evidence for the Big Bang theory.

    “Some scientists believe it to be infinite.”

    I assume you talk about people with ideas of a cyclic universe. If yes, then please consider that even these people agree that the Big Bang theory describes the universe right for the last 13.7 billion years, and only disagree about what happened in the first fractions of a second. I. e. to those people, the 13.7 billion years figure is essentially also right – it only does not describe the age of the universe per se, but only the age of the current cycle.

  76. #77 armtrack
    August 4, 2009

    scientists just made the discovery and did the test that objects can go faster then light

    http://en.wikipedia.org/wiki/Faster-than-light

  77. #78 Floyd
    August 4, 2009

    “Expansion or not, the age of the universe can never be proven…”

    You’re wrong. According with the WMAP measurements the age of the universe has been proven with a 99% of accuracy. See wikipedia.

    “..Some scientists believe it to be infinite.”

    You’re wrong again. Size and age are different things.

    “So, I fail to see the point of that statement.”

    Yep, you’re right. You failed.

  78. #79 Flemming Jacobsen
    August 4, 2009

    @jdhuey
    I think i see it now. Thanks!

  79. #80 Mu
    August 5, 2009

    Bjoern, rephrased: Is redshift related to age, distance, or both? As an example, if a 5 billion year old object is 5 billion light years from us and the light reaches us now, does it have the same redshift as a 5 billion year old object that seems to be 10 billion light years away due to expansion? Or can that not happen because all 5 billion year old objects will have the same virtual distance from us when the light reaches us now.

  80. #81 Ninjarabbi
    August 5, 2009

    How do we know we’re looking in the right direction?
    Maybe there is more stuff to be seen a little to the left?
    My question sort of fits with the ballon scenario.

  81. #82 Riya
    August 7, 2009

    Arg… so then, what is space?

  82. #83 Rocko
    August 7, 2009

    So if the universe is a balloon expanding and we understand that perfectly, then–why is there no equation or explanation for the girl? If one area is expanding then another should be contracting. I’m sure there must be an explanation for the girls lungs. Also, with virtually everything we observe in the universe expanding in a non-linear, but spiraling manner….are you certain that the universe itself is not spinning as it expands also?

  83. #84 Spanu Dumitru Viorel
    August 7, 2009

    There were opinions that Apollo 11 has never been on Moon . One said that the Eagle , the module that ” land ” on the Moon didn`t make print of its landing foots in the dust of the Moon . I saw a picture of the footprint of an astronaut in the dust of the Moon . The dust seems to have a height of several centimetres . When Eagle was getting close to the surface of the Moon , at about 3-4 metres , the reactive jet of its engine which was directed downwards spread the dust on a surface of several square metres , and let the rock of the Moon uncovered by dust . So , considering that the rock of the Moon has a medium toughness and also the landing foots of Eagle has a certain , not very small , surface , it is absolute normal that the landing foots of Eagle didn`t let any trace .

    Spanu Dumitru Viorel

  84. #85 Mark
    August 7, 2009

    How long will we be making up dates and lengths of time before we just go with what God has already said what he did to create the universe, just beleive it. He said, he created it all in 6 days and rested for one, then has been working ever since to keep his creation on track according to what he wants done. You can’t change the fact that your going to die some day and meet your creator whether you like it or not. If you reject him in this world, then Hell is where you will go because thats what you wanted, you just have to live with your choice for all eternity. If you chose not to beleive in God then you will be kicking yourself for all eternity knowing that Jesus was right and you were wrong. I wouldn’t wish hell on my worst enemy. Reason is the enemy of faith. It takes just as much faith to beleive in no God as it does to beleive in one. Only one path leads to life after death and that is Jesus Christ, all others are deceptions from the devil who is the liar who is the destroyer of life.

  85. #86 Jibreel
    August 8, 2009

    Mark, this is what is assumed God said in the Bible, however since the actual ancient text does not exist any more in the original language, we could say this is an inaccurate translation: 6 days in no way means 6 days, rather 6 time frames.

    In the Qur’an it is all explained way better, and in the original language.

    PS1 Oh yeah, in the Qur’an there is a statement that God created the universe and has been EXPANDING it since! Now this is something we did not know until some mid 19th century, cannot remember the exact date.

    PS2 Since when God needs rest? ;)

  86. #87 Paul McBride
    August 9, 2009

    Each observer is at the center of it’s own universe. All of which you describe seems reasonable, but it is an illusion. The light from the edge of the observable universe does not limit the actuality of an infinity of universes larger than the observable one. The redshift of light is due to its approach to the observer, and all observers anywhere in your description of the universe or even in the unobservable beyond will see and experience the same properties you describe, happily so. My question? You say it is like a balloon. If one expands a balloon enough one gets a “BIG BANG”. and that should put an end to all of the conjecture!

  87. #88 Paul McBride
    August 9, 2009

    Each observer is at the center of it’s own universe. All of which you describe seems reasonable, but it is an illusion. The light from the edge of the observable universe does not limit the actuality of an infinity of universes larger than the observable one. The redshift of light is due to its approach to the observer, and all observers anywhere in your description of the universe or even in the unobservable beyond will see and experience the same properties you describe, happily so. My question? You say it is like a balloon. If one expands a balloon enough one gets a “BIG BANG”. and that should put an end to all of the conjecture!

  88. #89 Burnerjack
    August 9, 2009

    I’ve always thought that the Primordal Point of energy was dimensionless as pure energy is assumed to be (by me). It was contained in “non-space”, therefore had no space in which to coalese into matter (E=MC^2).
    Gravity is a distortion of spacetime, therefore, is not a force at all but an observation and as such cannot be included in a Unified Field Theory or TOE (theory of everything). Lastly, The Big Bang is but one of many, meaning the true size of the universe is even bigger than comprehension. Just my crazy thoughts. What do you think?

  89. #90 MarkSeid
    August 10, 2009

    Suppose we were in a Newton-Hubble Universe (NHU) – no Michelson-Morley observations, no Fitzgerald-Lorenz equations, no Einstein special or general relativity; but data that showed increasing red-shifts from further stars.
    How rapidly would this NHU diverge from what we see and calculate about the real universe? Or, alternatively, what could we deduce and explain without jellying our brains?

  90. #91 Mike
    August 10, 2009

    What is the age of the Milkyway? Why can’t we look that many light years away and see ourselves? or would that require traveling faster than the speed of light? I am so confused.

  91. #92 Mike
    August 10, 2009

    O.K. If you could go faster then the speed of light couldn’t you get to your destination and turn around really quickly and see yourself coming?

  92. #93 Mike
    August 10, 2009

    Alright, let me see if I got it. Nothing is really moving, the universe is expanding so everything is moving relatively to everything else?

  93. #94 Doc Merlin
    August 10, 2009

    @Ethan: “Massless particles can only stay still if you have a medium where the speed of light in that medium is infinitesimally small. Theoretically possible, but not yet discovered.”

    Yes it has, its been done in the lab with condensates.

  94. #95 Torbjörn Larsson, OM
    August 15, 2009

    How rapidly would this NHU diverge from what we see and calculate about the real universe?

    I fear the answer is very mundane and not what you asked for, as AFAIU fields as we know them couldn’t exist. The discrepancy would be immediate, no light, no matter, nothing.

  95. #96 Torbjörn Larsson, OM
    August 15, 2009

    How long will we be making up dates and lengths of time

    Funny idea, from someone who waves a made up text around.

  96. #97 Erik P
    August 21, 2009

    Just wondering how the red shift tells us that the univierse is STILL expaning? Would there not be a red shift for some period of time after the universe began contracting?

  97. #98 Erik P
    August 27, 2009

    Ethan, really am trying to understand this. But when I read this I think that if the red shift was caused by expanding universe, wouldn’t the red shift continue even if contraction started to occur, at least until the stretched light waves are back to original wavelength? Or what am I missing.

  98. #99 Tim Walker
    September 3, 2009

    @Ethan: If the universe were to start to contract, we would need for the light from the nearest universes to reach us to confirm this, since it would only be visible on this scale. And since contraction/expansion becomes more and more visible the farther a universe is away from us, we’d probably need to wait even longer to be sure. So unless these things happened hundreds of millions to billions years ago, we’ll never know the answer. However, everything points to expansion increasing over time, so something drastic would have to happen, or our understanding of the universe to be drastically wrong, for it to change back to contraction.

  99. #100 Ethan Siegel
    September 3, 2009

    Erik and Tim,

    If contraction started to occur, we would be able to observe it. The nice thing about having the whole Universe to look through is that when you see something nearby, the light only traveled for a short amount of (recent) time. When you see something farther away, the light traveled for a longer amount of time, including the recent time. So by probing objects at all distances, we can learn about how the entire Universe expanded over its entire history.

    We find that it expanded the same in all directions, the expansion was faster in the past, and the expansion rate is leveling off, not dropping to zero and definitely not contracting.

    I hope this helps clear things up.

  100. #101 Raimonds Cirulis
    September 6, 2009

    Well, I become to the same conclusions. I just finished my calculations and found this article. Everything match!

  101. #102 Erik P
    September 11, 2009

    Ethan, thanks. So I am understanding that you are saying that we can comfirm expansion from redshift even looking at closer objects, just a few light years away. We are not only depending on the shifts of objects from millions or billions of light years out. I think I understand now.

  102. #103 Universe Man
    October 14, 2009

    Please answer on this question – Does the density of galaxies drop off as the distance away increases?

  103. #104 Jim Jones
    March 10, 2010

    Ethan: My question is this (if you ever come back to this post)

    Will the light that has been comming to us from “the other side” of the big bang eventually distort our view of the “recent” visible universe?

    More specifically: Will the light we see from galaxies now (our side of the big bang) eventually be “caught up” to light from the other side of the big bang (assuming galaxy formation happened on the other side of inflataion too) and then instead of having mostly black light in space there will be so much to see that in effect we will see 2 evoutionary periods (our present (and older) evolution coupled with the evolution of the galaxies beyond the visible universe?) So in essence, after a certian amount of time (i guess the initial distance of the big bang) passes by us then we will see the “other side” of the universe evlove from “ground zero” again?? I hope that was not to oconfusing

    J

  104. #105 Bjoern
    March 10, 2010

    @Jim Jones: I’m not Ethan, but I’ll try… ;-)

    I’m not entirely sure what you mean with “the other side of the big bang”. Probably you mean in the balloon analogy the point which is on the exactly opposite side from us, the point with the furthest possible distance to us? If you mean that, then the answer is simply: if the universe keeps expanding as described by the current model, the light from that point will never be able to reach us.

    If you mean something different, please explain.

  105. #106 Luis Biarge
    May 12, 2010

    I’m against Universe expansion:

    For example a question: – The universe expand in any radius at light speed: How can accelerate? At what speed expand the diameter (radius x 2)?

    The expansion need to be decreasing by unit of space, in your note “It’s a velocity-per-unit-distance. Let’s say that it’s 0.4 cm/second per centimeter.” in this case the Universe soon would exceed light speed.

    Another question over this: – The expansion speed is constant (or nearly) and distance is growing: How can decrement by unit of space? How can to be instantaneous and inexhaustible in all point according to Hubble’s law? How can compute this decrement and instantaneously in all the points?

    This and more, also doubts, proofs and hypothesis in http://bigbangno.wordpress.com

    Sorry if disturb.

    Thanks.

  106. #107 DaveH
    May 13, 2010

    “I’m against Universe expansion”

    Maybe if you suck really hard…

  107. #108 Bjoern
    May 13, 2010

    @Luis Biarge:

    The universe expand in any radius at light speed

    No, it doesn’t! And I don’t know where you got that idea from…

    The expansion need to be decreasing by unit of space

    What does “unit of space” mean?

    in this case the Universe soon would exceed light speed.

    Not the universe itself (the universe itself has no speed) – but objects in the universe can recede from each other with speeds greater than light speed. This does not contradict Special Relativity, since this speed is not about a movement inside space, but about the expansion of space itself.

    The expansion speed is constant (or nearly)

    No, it isn’t. In fact, it grows almost exponentially!

    How can decrement by unit of space? How can to be instantaneous and inexhaustible in all point according to Hubble’s law? How can compute this decrement and instantaneously in all the points?

    Sorry, but I don’t understand what this all is supposed to mean. Could you please try to rephrase it?

    This and more, also doubts, proofs and hypothesis in http://bigbangno.wordpress.com

    I’ve briefly looked at that webpage – and it is full of more of strange sentences like the ones above. You are apparently not a native English speaker? If yes, please seek someone who can help you write proper English – it is simply incomprehensible what you mean with most sentences!

  108. #109 crd2
    August 19, 2010

    Sorry, but as i read his post all i could see in my mind is the geico caveman typing.

    “How can accelerate? At what speed expand the diameter?” Said the caveman in his lab coat.

  109. #110 Clark
    December 9, 2010

    Perhaps there is a need to show examples of different kinds of science blogs: individuals, corporations, organizations, non-profits, advocacy groups, scientific journals, popular science magazines, newspapers, scientific projects, etc. all have examples of good science blogs they are running. For example, the article should mention Andrew Revkin and Olivia Judson as bloggers for 642-661 dumps New York Times. Various official editorial blogs at Nature, PLoS, etc. Prominent science journalist/writer’s blogs. Blogs that are an actual part and parcel of a local science journalistic project

  110. #111 herb ridge
    January 16, 2011

    What I can’t wrap my mind around is what was there before our universe. If our universe was taken out of the picture what would be left?

    Is there a book that anyone could recommend that discusses finite/infinite universes. i find this discussion extremely interesting but when I try discussing it with anyone I get blank stares.

  111. #112 Shailesh Kadakia
    February 25, 2011

    Often for scale of universe, curvature introduced by gravitation is incorporated in computations (Theroy of general relativity from Einstein). In the vast universe, gravitation force arises from vast galaxies. Question:If celestial objects in galaxies are moving at very high speed (Sun 220 km/s) how the spacetime curvature is determined at a location considering finite speed of propagation of gravitational force being same as the speed of light?

  112. #113 sumit
    May 23, 2011

    aksfdka

  113. #114 Lennon Aldort
    June 30, 2011

    Great article! I actually just posted a blog about the enormity of the universe myself. I read that it’s 93 billion light years across. I see around 50 billion in places, and around 150 billion in others.. so I just went with 93 billion for my post. It’s doesn’t really matter that much, it only applies to a small portion of what I say.

    http://lennonaldort.blogspot.com/2011/06/universe-is-really-really-big.html

  114. #115 Aleck Tricity
    September 10, 2011

    Ethan,

    I came here hoping for an explanation as to how the universe can be bigger than 13 billion light years.

    Your explanation with the ant and the balloon is brilliant. Simple, effective, and insightful.

    Thank you very much.

    Aleck.

  115. #116 Hua En
    October 28, 2011

    where do all the matter sucked in by black holes go? Do they come out as dark matter and dark energy?

  116. #117 Colin
    December 1, 2011

    Nice explanation but there is still one part I do not understand. Since the universe is expanding faster than the speed of light for it to grow to almost 50 billion light years in less than 14 billion light years how does the light from a star 50 billion light years away reach us in under 14 billion light years less the time it took the star to reach the its position given the fact that since the universe is increasing in size the light would have to travel further than the star originally traveled?

  117. #118 orien rigney
    January 16, 2012

    If a person two billion L.Y.s from earth has a simultaneous thought process as someone on earth, will time be relevent?

  118. #119 mario georgina
    February 16, 2012

    Would a person on a planet 10 lys away not come to the exact same measurements as us but see galaxies on the far side away from us that we can no longer see and we see galaxies on our far side that the other will never see?

  119. #120 P Caryota
    February 22, 2012

    How about explaining that the universe expands at some rate but the light we see from the rest of the universe travels around the balloon not through it. So even if the diameter of the universe was 2 * 14.7 billion light years, the distance around to the far point would be Pi times that… This would get to beyond the 46.5 billion light year mark.
    What would you use as the volume of the universe? How thick is the balloon’s skin?
    No wait… I’m still blown away.

  120. #121 Steve
    March 11, 2012

    I am one who believes in a parallel universe or dimension that we cannot see with our human eyes. What has peaked my interest for many years is what force or particles are beyond the visible universe. It seems to me that the universe is infinitely large, if it is not, what is beyond the 46.5 billion light years?

  121. #122 Bob
    March 29, 2012

    Expanding space? Sounds more like a fudge factor to explain away the observation that matter is traveling faster than light!

  122. #123 Jon
    April 3, 2012

    Okay, so the observable universe has a diameter of about 93b light years and are 13,7b years old.

    Are ther any estimates for the whole universe ?

    Is it then 93b light years in the other direction as well?

  123. #124 Peter Whitlock
    April 9, 2012

    No evidence of this bad math exist!
    the known Universe is expanding BUT no one can say it is expanding in a sphere or any kind uniform way! it can be getting LONGER and so is not expanding in places but crossing itself or splitting apart. The dark flow effect only shows what is EXPECTED in a NON BIG BANG EVENT and a star creation direct from clouds of Hydrogen cross paths. The results are exact same BUT has no need to rapid expand or Trillions of degrees of heat or reason to COOL to the heat of stars start.

    The expansion of the KNOWN Universe int o UNIVERSE only permit about 13.7 billion light years to be seen and in no way shape or form does it permit the Universe to be expanding at near light speeds… inflation can be a LOT SLOWER and can be at the model of hydrogen explosions not inflation of big bang… Universe can be a lot smaller than claims of 46 billion light years
    It can be 25 or 30 or 20 even… the size can’t be chosen with light speed only or near it… a slower expansion is also possible as well as exact DIRECTION to the event.

    spheres and inflation THEORY is THEORY only.
    Other starts and reasons can exist!

    The possible GIANT SINGULARITIES drqag behind them vast amounts of debris and GAS.
    The possible collision of 2 such objects and the gas and materials they each had.
    The FLY BY of singularities and all they carry behi8nd them like a comet collide to make stars.

    Any dense cloud of Hydrogen with 2 different directions permit the expansion of the known Universe with no Big bang needed to cook up the parts. The expansion can be the same or less fast, and still have directions over the “all directions at once”.
    Nothing is clear or sure and WHY they call it THEORY!

    The only truth you can be sure of is the start of stars origin.
    it does not need a big bang
    it only needs a vast cloud billions of light years across to hit another of the same nature… presto! You can fool yourself with big bang all you want but it does not answer anything!

    Shape of the Universe CAN”T be told as no limits have been found to use to determine the shape… till then it will always say flat as nothing other is there to find to judge any variations to say other. It was always IMPOSSIBLE to judge the shape of the Known Universe with no real edge… end of visibility is NOT and edge! it is limit of sight ONLY.

  124. #125 chandan
    April 17, 2012

    Is it possible that a star would form at a distance 12.8 billion light years of present universe within only 822 million years?

  125. #126 Ken Cronin
    April 23, 2012

    We use C as a constant until all theoretical work arrives at a dead end, then we conveniently say that in one instant we will allow light speed to be violated. I guess it’s easier than admitting that some of the hard work you put into studying this stuff may be wrong. If I am observing light that originated 13 billion years ago, then that means the source object was 13 billion light-years away 13 billion years ago. How long did it take to get there before the light was emitted? Go back and read Einstein’s original writings – then think on your own like he did. He sought facts, not fame like half the nit-wits who keep building on unproven theories.

  126. #127 ali
    CA
    May 23, 2012

    i thought nothing or nothingness can travel faster the speed of light.

  127. #128 Peter
    Mexico
    October 23, 2012

    If we can see 13.6 lightyears far in every direction that would mean we are exactly at the center of the universe. Preposterous!

  128. #129 Wow
    October 23, 2012

    No more than because the horizon is 3 miles away from you in every direction when you are standing on a boat in the middle of the ocean means you’re at the center of the earth.

  129. #130 David
    January 26, 2013

    What I’m wondering is, over the next, say, 1 billion years, is that 46 billion light years radius going to steadily increase for us (i.e. are we going to slowly see more and more of what’s currently just at the edge of the observable universe), or does the increasing expansion rate of the universe mean our observable universe is either only going to get smaller or stay the same? What about 2 billion years from now, or 3, 5, or 10 billion years from now, will there come a point where things are expanding so quickly away from each other that even things we can see now ‘drop off’ the observable universe (putting them forever out of reach in any sense)?

    It seems to me that the expanding universe is just one more argument to try get our butts into space faster rather than later .. it’s even more ridiculous that we blow trillions on wars in which we try knock each other back into the stone ages, but we won’t spend even spend relatively paltry billions on space exploration. Imagine all the money from just the Iraq, Afghanistan, Gulf and Vietnam wars, had all been poured into scientific and space research – we would ALREADY be living in an era where we had cured aging and where we were living on Mars and terraforming it, and talking about how to get to the nearest stars.

  130. #131 Wow
    January 26, 2013

    the edge of the galaxy will retire quicker than the light can get to us faster than light speed.

    Therefore we will see less and less of the universe over time.

  131. #132 Peter Taylor
    London
    January 27, 2013

    I fail to see that we can actually see 46.5 billion light years into space, because those light photon’s are still on their way to us. The light photons that we are actually seeing are 13.772 light yeas old. But that ‘event’ horizon that we are seeing is in the past, not now. That point ‘event’ Horizon has now moved 46.5 billion light years away. We cannot see the current point that light has reached, because it is still travelling towards us at 670 million miles an hour, and at 46.5 million light years away, we can never see it. Or am i just making it up!

  132. #133 David
    January 27, 2013

    “The light photons that we are actually seeing are 13.772 light yeas old”

    You mean, just ‘years old’. ‘Light years’ is the distance light travels in one year.

    “We cannot see the current point that light has reached”

    By definition, we see the current point that light has reached (that’s the only light we can see, because our sensors – our eyes – are here on earth where the light is now reaching – we can’t see light that’s still travelling toward us because those photons are still travelling toward us. And we can’t see light that’s already zipped past us because those photons have already zipped past us.). The light (photons) that is still travelling toward us is equally old (13.7 billion years), but emanates from a slightly further back ‘original distance from us’ (I think?). The 13.7billion year old light that is reaching us now was actually only something like 30 million light years away when those light rays originally started travelling toward us, and the expanding universe stretched them to 46 billion light years away, while the light plodded on its way toward us all this time.

    So if the 13.7billion year old light we detected last year started (say) 30 million light years away, then the 13.7billion year old light we detect next year is just the light that was (say) maybe 30.1 million light years away around the beginning of the universe.

  133. #134 Khristyan
    April 10, 2013

    Guys, the universe was created by God. I can’t believe people still talk about this pathetic theory of “Big Bang”. Not even renowned scients can explain how the universe formed. People are so ignorant these days. I can’t stand thinking that they can’t believe there is a supreme intelligence and force that made such wonderful things.

  134. #135 Wow
    April 11, 2013

    No it wasn’t.

  135. #136 Sean T
    April 11, 2013

    Khristyan,

    Please do yourself a favor. Take such ideas to a religious blog. This is a science blog. We wish to discuss SCIENTIFIC ideas here. If the universe were created by God (which is highly dubious, to be polite), science cannot arrive at that conclusion anyway; it’s not designed to consider anything supernatural. It can only consider religious claims insofar as these claims have observable consequences. For instance, fundamentalist Christians claim that there was a global flood that completely innundated all land on the earth. That claim has observable geological consequences, but the observed geological record is not consistent with such a flood. That seems to be the case for ALL religious claims with observable consequences; the observational evidence is not there.

    Even if I were to grant some validity to your claims, you are being quite rude anyway. If I were to walk into your church while your priest/pastor/religious leader was giving his sermon and start telling everyone that these ideas he was talking about were all crap, you’d be pretty annoyed with me. That’s precisely what you are doing here. If you want to discuss religion, there are other places to do so, please go there.

  136. #137 Khristyan
    April 12, 2013

    Sean T,

    I didn’t mention in any time that I believe there was a global flood, because this story is one of the ones parents tell their children at home. I don’t even go to church. You do not know what religion I believe, you don’t even know wether I believe or not. I just said that there are a lot of things scientists can’t explain, and if they can’t explain, why not believe that a greater intelligence created everything. Why will I keep worrying about something that can’t be explained? Most scientists don’t believe god, and that’s why they keep on trying to find a reason for everything. Remeber what I said, people are being so ignorant and narrow-minded nowadays, and if you felt outraged when you read my remark, I’m sorry to say but you’re this kind of person. Maybe my remark was rude, and I think it was, because I’ve just reread it and if I were you, I would feel offended, too. I apologize for being impolite, I just wanted to express my opinion, but that’s what I think and no one will change it. And as you said, this is a scientific blog, not a relationship site, so if you want to discuss our relationship meet me there OK haha. There’s no need to discuss, if you don’t believe God, I just can’t do anything.

  137. #138 Wow
    April 12, 2013

    What does “You do not know what religion I believe” mean or have to do with what you or anyone else has said?

    The religion you believe in is that God (whatever that is) created everything (however that happened). Which is complete bollocks: it answers NOTHING.

    “I just said that there are a lot of things scientists can’t explain”

    No you didn’t you claimed “Guys, the universe was created by God”, but you are a habitual liar, aren’t you, if it’s all in “a good cause”.

    “Remeber what I said, people are being so ignorant and narrow-minded nowadays”

    No. Why? Because your tirade is tiresome and of absolutely no worth whatsoever: it’s been done to death a million times.

    Have you ever, EVER, considered there is no god?

    Talk about narrow minded…

  138. #139 CB
    April 12, 2013

    “You do not know what religion I believe”

    Yeah, you’re real subtle, “Khristyan”. Doesn’t matter, though, the basic point Sean T was making is valid. There is no evidence of God — whatever God you might be talking about. There is evidence for the Big Bang. Tons of it.

    ” I just said that there are a lot of things scientists can’t explain, and if they can’t explain, why not believe that a greater intelligence created everything.”

    Why believe that over anything else — e.g. the universe just exists, inexplicably, with no creator? Why is your belief in a greater intelligence a consequence of science not being able to explain things? If they COULD, would you stop believing in God?

    “Why will I keep worrying about something that can’t be explained?”

    Why assume that things can’t be explained ever? It is certainly possible that there are things that can’t ever be explained, and I’m fine with that. But why not try?

    “Most scientists don’t believe god, and that’s why they keep on trying to find a reason for everything.”

    I do believe in God, and yet I still want to try to find a reason for everything. “God did it” may provide spiritually satisfying bedrock, but it’s as intellectually satisfying as “*shrug* I dunno…” Personally I don’t think God created this vast and amazing universe that appears to run on logical, mathematical rules, and which also has the potential to create intelligent life, just so that life could AVOID figuring out how this amazing universe works.

    To do so is the ultimate in deliberate ignorance. It’s closing your mind on purpose to the nature of reality. I don’t think you have a leg to stand on throwing those phrases at others.

  139. #140 Sean T
    April 12, 2013

    Khrystyan,

    I am not personally outraged that you believe in God. I wouldn’t be personally outraged if you believed in the tooth fairy and santa claus either. I am just pointing out that religious discussions don’t have a place on a scientific blog. If I were to go into ANY church (whether you have a church or not is irrelevant here), and start telling everyone there that God doesn’t exist and that the pastor/priest/cult leader/whatever is just lying to all of you, what would you think of my behavior? Is it appropriate? Of course not, and I would expect that the congregation would toss me out on my ear without being particularly civil about it. I was merely pointing out that your behavior here is analogous.

    Further, I don’t care about your personal beliefs. The examples I put forward are merely examples of religious ideas that have a potentially testable observational basis. AFAIK, all such testable religious ideas have turned out to be false. If I am wrong, please feel free to enlighten me. Further, such a religious discussion is precisely the type of discussion which would NOT be completely out of place on a science blog. If you have a religiously-inspired idea that has testable consequences, then whether you like to admit it or not, it’s actually a scientfic idea. Of course, more likely than not, it’s not a valid idea, but at least there’s an objective way to test it, which does make it scientific.

  140. #141 Khristyan
    April 12, 2013

    HAHA Guys, I can see you all are very smart. I admire all of you for being such interested people. I just wrote these remarks because I wasn’t doing anything at home in fact, I just wanted to have some fun. I’m so sorry for being so inappropriate, it’s because

  141. #142 Khristyan
    April 12, 2013

    HAHA Guys, I can see you all are very smart. I admire all of you for being such interested people. In fact, I just wrote these remarks because I wasn’t doing anything at home and I wanted to have some fun. I’m so sorry for being so inappropriate, it’s because I wanted to see what you guys would have in response. I don’t know how the Universe was formed, and if I really believed that God created it, I wouldn’t have searched such thing on the internet. I believe in God, but I also believe in science too. And everything related to the universe, planets, stars, astrology in fact amazes me. I can see you defend your point of view and I believe everything you say, I was just being annoying, and I’m so sorry for that. I won’t make fun from serious things like this again. Sean T., this is directly for you, I was so rude to you and I am really sorry man, I would like to have such an incredible mind like yours, you were able to make me get lost in my own thoughts. I just want to say that this blog is wonderful and that your remarks are all so accurate. Maybe you may be mad at me or even worse, but I’m really sorry. I promise next time I write another remark it will be serious and about this subject OK. Again, I apologize for being so stupid. :)

  142. #143 Wow
    April 13, 2013

    So not just lying for jesus, trolling for him too.

    Awww, maybe if you had something in your life that was worth something, you wouldn’t have to punctuate your ennui with trolling. Try letting some rationality into your life and live a better existence :-O

  143. #144 Khristyan
    April 13, 2013

    Man, go suck some dick and shut up!! I didn’t write that for you, so keep your nose in your face and stop putting it where you aren’t mentioned. I live my life the way I want, and mine is probably better than yours. Why don’t you suicide and make the world a favor haha.

  144. #145 Wow
    April 13, 2013

    Yup, not able to manage trolling, you’re trying VERY BAD trolling.

    Get a life, kid.

  145. #146 Khristyan
    April 13, 2013

    [[Comment removed and user banned by the blog owner.]]

  146. #147 Wow
    April 14, 2013

    Though his previous post were bad enough for banning, I would have preferred that a stern warning were given first: when there’s no apparent moderation going on, trolling kids will jump further and further into the abusive zone. If the only response is to wait until the post is so offensive it can’t be printed and THEN banhammer, very little is learnt about the nature of the moderation.

    Note: I’ve avoided “boundaries”, since it isn’t a boundary, more like impressionist painting by numbers. There’s a long swathe of grey area and you don’t have to necessarily go far into that grey area to warrant banning if you’re postings are all camped in there.

  147. #148 Ethan
    April 14, 2013

    Wow,

    There are a few things one can say that are so offensive, hateful or destructive that I have no qualms banning a user then-and-there, without warning, for a single comment. They are listed under my comments policy.

    I was keeping an eye on Khristyan (as I’m currently keeping an eye on a few relatively new commenters) when he went way over the line. But yes, I hate having to moderate and so I do it as little as possible. This time, my hand was forced.

  148. #149 Surreptitious Evil
    April 14, 2013

    “Does the density of galaxies drop off as the distance away increases?”

    No. If you are looking at some ‘now’ time view across space, then galaxy density appears to be dominated by the major structures. But these are essentially invariant as distance from Earth (or any other pov) increases.

    If you are considering what we can see, then actually density appears to increase as we look away, because we are looking back in time (when there was less expansion.) Until you reach the point when galaxy formation was just starting.

    “If a person two billion L.Y.s from earth has a simultaneous thought process as someone on earth, will time be relevent?”

    One of the results of Lorentz and Poincare’s work, and appearing in Special Relativity is that “simultaneity” is a concept that is flawed when dealing with multiple co-moving observers. Some events you and I, limited to the Earth’s moving reference frame, might agree are simultaneous are likely to appear as disconnected to an observer moving quickly with relation to us.

    “Is it possible that a star would form at a distance 12.8 billion light years of present universe within only 822 million years?”

    I think you are asking was it possible for stars to form 800 or so million years after the big bang? Well, yes. In fact the earliest formed much earlier, a mere 200 million years after the big bang, according to WMAP data analysis.

    Why? Dark matter clumping (not or minmally affected by the high energy photons bashing around) as star seeds? Our current models of stellar formation being inadequate? Something else? Quite possibly. But, as the sage said, if the evidence contradicts the theory, bin the theory …

    (Or, post-Milliken & again post OPERA) – check the evidence very, very carefully for fudges, error and other distortions. Then bin the theory.

  149. #150 Wow
    April 14, 2013

    John, that link in arxiv is worthless. The majority are talking shit. Other papers aren’t talking about aether.

    Pete is just walking the same tired old line chelle does: proclaim Einstein said it was there (and ignore the fact that a decade later after wasting his time, he said no such thing exists).

    Aether is woomancer bullshit and the thread I’ve pointed Pete to is where this goes.

  150. #151 Wow
    April 14, 2013

    Above went to wrong tab…

  151. #152 Wow
    April 14, 2013

    I suppose that the latest “christian” troll didn’t give any time, going all the way from 0 to over 9000 in nastyness. Quite old-testementarian of them, but VERY un-christian.

    It was only a thought about how best to keep things somewhat civil. If people know whereabouts the lines are drawn, it’s easier to tell someone getting canned that they were given fair warning.

    Some teenage twits really don’t care about warning, though. And they don’t risk having their arse handed to them for this, so they get all hard-man over the internet.

    A bit of a bugger.

  152. #153 Bryan Walters
    April 14, 2013

    Oh my god, stop talking about this guy. He won’t be able to annoy you anymore, so let us keep this place respectful. It’s a science blog, isn’t it? So let’s talk about science OK.

  153. #154 Steve
    UK
    October 24, 2013

    Excellent article and discussion. I saw this because a media article today talked of objects being 30 bn ly away. I thought they had made the error, but have learned now that actually I was the one not looking at it the right way. Always good to learn something new, and the universe has grown immensely today (my understanding of how big it is, I mean).

  154. #155 Charlie
    Australia
    November 1, 2013

    Hi Ethan

    I was wondering about the expansion of the universe the other day and a thought occurred to me – and that was rather than the universe expanding could it be that we are shrinking – so that the universe just looks like its getting bigger ?

  155. #156 William
    Columbus, Ohio
    January 2, 2014

    Here is a thought. String theory suggests that there are a half dozen of so compactified dimensions. What if time is a dimension that is neither fully compactified nor fully expanded (like spatial dimensions). Does this thought make any sense?

  156. #157 William
    Columbus
    January 2, 2014

    In other words, time represents a dimensiom that is seeking to unfold but that remains trapped in a partially compactified state.

  157. #158 Dan Rivers
    United States
    January 10, 2014

    I understand your analogy but it seems you are saying that the edge of the universe is now 46 B Light years further away that it was 14 B L Y ago. And the ant would be the same size but his world has expanded. So he would be correspondingly further away from his goal since it expanded under him.

  158. #159 Michael Kelsey
    SLAC National Accelerator Laboratory
    January 10, 2014

    @Dan Rivers #158: You’ve got it, exactly!

    It’s not so much a true “edge”, as it is “the place where the oldest light we see right this minute was emitted.” There may well be (and almost certainly is!) much more universe beyond that point, but there hasn’t been enough time for the light from those places to get to us yet.

  159. #160 John Duffield
    January 11, 2014

    @Michael #159: Some people say “the universe is flat so it must be infinite”, but that’s a non-sequitur. Press them on this and they will even claim that the universe has always been infinite, and was even infinite at the time of the big bang. Others will say “it looks pretty flat so it must have a huge radius of curvature and must be very very large”. IMHO that’s more reasonable. But IMHO there is another option: the universe is truly flat, and it has an edge. A true edge.

  160. #161 Michael Kelsey
    SLAC National Accelerator Laboratory
    January 11, 2014

    @John #160: As I had pointed out to me in one of Ethan’s blogs last year, “flat” does not imply _either_ a “huge radius of curvature” nor infinite. A torus (or in this case, a hypertorus) is “flat” in a valid measurement sense, but is both finite and unbounded.

    It is certainly possible that the Universe has a true edge to it. However, if that edge were close to the size of the observable universe (i.e., ~ 50 Gpc today), there would be clear effects on the power spectrum in the CMB and BAO (in particular, there would be a cutoff to the possible oscillation wavelengths). Such effects are not, in fact, seen, so we _know_ that the size of the Universe is larger than some finite multiple of the observable radius.

  161. #162 Larry
    Las Vegas, Nevada
    February 11, 2014

    I’m confused. Objects exist in space, i.e., they take up space. Therefore, if space is expanding, do not all objects within it expand in size accordingly? You see, I’m puzzled why an object appears to remain the same size, while only the exterior space around it is expanding.

  162. #163 Michael Kelsey
    SLAC National Accelerator Laboratory
    February 11, 2014

    @Larry #162: It’s a matter of scale, and you can do the arithmetic. The present expansion rate, derived from observation is about 70 km/s per megaparsec. That is, two galaxies exactly one megaparsec from each other today are separating at a rate of 70 km/s; galaxies two megaparsecs apart are separating at 140 km/s, and so on.

    So what is the effect of the cosmological expansion on, let’s say, the solar system. The radius of the solar system (which I take to be the outer edge of the Kuiper belt, just for convenience) is 50 astronomical units (AU). Now, 50 AU is 2.42406841 × 10^-10 megaparsecs (that is, 242 _trillionths_)! So, an object at 50 AU would, possibly, be receding from the Sun at a rate of 70 * 2.42E-10 = 1.6E-8 km/s, or 16 microns/second!

    For comparison, soalr escape velocity at 50 AU is 6 km/s. So the Sun’s gravity is much, much, MUCH stronger than the cosmological expansion.

    You can, with the help of Google and Wikipedia for finding the numbers, do the same calculation for larger objects, like individual galaxies, clusters of galaxies, and so on. What you’ll discover is that for gravitationally bound objects we know of, up to the size of galactic superclusters, the binding gravity dominates the expansion.

  163. #164 Sassy Lou
    NY
    March 18, 2014

    Never believed in the big bang. If everything came from one point (the big bang) then why are there images of entire galaxies colliding while from coming in from perpendicular angles? When something explodes..doesn’t it explode out in the same direction? Yet you can see two galaxies coming at each other from a perpendicular angle.

    Explain….. Exaclty…..

    Thank you. Case and point

  164. #165 me
    here
    March 27, 2014

    Question is if a light beam was emitted right now how long would it take to reach the other side of the universe.. the universe may have expanded beyond 13.7b ly but its expansion is carrying the matter and energy contained with it. So as it continues to expand a new light beam will also get carried with it. Still expanding it would have to take at least 46b ly (if thats the accepted value), and perhaps double or 10x that since the expansion is increasing at large distances.

    Right angle galaxy interactions are due to previous gravitation interaction like balls on a pool table.