Questions / Suggestions

Please look through my bad english. It is not my native language.

Here you have mij email. Plz do not spread my email. TY

I know i'm coming into the discussion late but I can't find an answer to this question. Since no one knows what dark matter or dark energy are, how can we know if or how they might effect red shift?

@Lynn #2: Ethan has lots of much better explanations than I can provide, but I think this is simple: both dark matter (DM) and dark energy (DE) are _defined_ by how they affect our cosmological observations. That is, DM _is_ "whatever the stuff is that makes galaxies and clusters much more massive than the things we see with light", and DE _is_ "whatever the effect is that is causing the expansion rate to increase with time, instead of decrease."

The big research project is to try to understand what physical stuff is causing those observations.

Michael, That still doesn't answer how or if they effect red shift.

@Lynn #4: I guess I'm not entirely clear on what you're asking.

1) The expansion of the Universe causes us to observe a redshift of light emitted by distant galaxies. To the extent that the expansion rate of our Universe (containing DM and DE) is different from what it would be if it only contained baryonic matter, the redshift we observe is "affected" by DM and DE.

2) Concentrations of mass cause a _gravitational_ redshift of light leaving their vicinity. We observe this on Earth and on the Sun. I'm not certain whether the effect is large enough to observe for galaxies or clusters (I rather doubt it). However, if the effect is observable, then the DM present will lead to a larger effect than if only the baryonic matter were there.

@ Lynn

It's the other way around actually. I will try to use an analogy. Imagine your friend goes to another city by car. And he tells you that he will call you once he arrives. And let's say that the car is traveling 100km/h and the city is 200 km away. Now, under normal circumstances, you would expect him to call in 2 hours. But he calls you 1:20 min. You know his car can't go faster than 100km/h and you now when he left, thus the only conclusion you have is that "something" made his car go quicker... or something shrunk the road.

We observe the red/blue shift. And since "c" is constant, we can only conclude that "something" messed up the wavelenght.

One other important thing. Redshift caused by dark matter is different than the one caused by dark energy. DE and DM act very differently.

p.s. DM acts as a regular gravitational shift. With lensing and so on. DE is a peculiar one. It acts on spacetime itself.

Thanks guys you really cleared it up for me.

I've noticed a very interesting optic effect today on my wall. A small object on my coffee table cast a shadow on the wall, but a reflection which is not really visible on the glass, also cast a reflection of same opacity and size at exactly 90 degrees. Table top is not a mirror, but a transparent glass.

Would appreciate very much if someone could explain what happens to light in this scenario. Question is about reflection casting a shadow in a particular case.

I tried googling for it, but couldn't find anything useful. Having read much about QED lately, am really curious how this effect occurs in QED terms. From point of view of the wall and some photons, both object and reflection are really the same, they cast exactly the same shadow. How come reflection's shadow occurs in the first place, why isn't it i.e. lighter or darker? But also it's a transparent glass, yes from some angles a faint reflection is observed, yet it seems there's an angle where it's 100% reflected.. weird a bit again..

here is a drawing I made to help illustrate it.
http://oi44.tinypic.com/2a4yge8.jpg

Again, thank you if someone can explain in detail, or at least point me to correct articles. Maybe this effect has a technical name, that could help also. :)

And sorry if this isn't an appropriate topic... :)

p.s. sorry... first sentence should read " but a reflection which is not really visible on the glass, also cast a SHADOW of same opacity and size at exactly 90 degrees, ON THE WALL"

* bump :(

Test.

Bump test.

where can i read answers ?

Scientists often state that they do not know what time is, but know how to measure it accurately, which is an oxymora. Time is a system of information exchange, how God and men relate events with respect to the rotation of the earth: what you plan to do tomorrow; what you did last year; how long Jesus was in the tomb; how long it took God to create the universe; or how fast something travels all relate to the rotation of the earth. While gravity may affect time-measuring instruments, that is not proof that gravity affects time. If it did then two observers of a star, both located at exactly the same latitude but at a different longitude, such that one observer is a mile higher than the other, would observe the meridian containing the star cross their zenith at different times, with that difference in time increasing each year. You should recognize that this is impossible. Time slowing down or speeding up with speed is also impossible, but a concept derived from Einstein’s fallacy. His fallacy, while observing the clock at the train station and imagining the effects of observation of the clock as the train sped up to hypothetical speeds, was to ignore the time taken for the image from the clock to reach the point of observation. The clock did not slow down, nor did time.

"Time slowing down or speeding up with speed is also impossible,"

Since gps satellites would not give correct results without accounting for the effects of time dilation, and since it has been experimentally verified in other ways, your comment was demonstrated to be false before you made it.

when dark matter is discussed, it almost always talks in terms of something being "the" dark matter particle. is there a reason to assume that it's not a mix of several kinds of particle?

The more agreeable I see the way people agree only tempers my soul to double fact check.

Ragtag...Way

No, nothing stops it being multiple types of matter, Jerry. It's called "Dark Matter" rather than "THE Dark Matter", except where the context would make it generic, such as "The library is where you go to get a book to read".

I understand that the Inflation Theory has the expansion of the universe being driven by an Inflation field that had negative pressure and hence pushed on space (negative gravity). And that as space expanded more of the field was created which pushed more. Hence the run-away inflation event that flattened the universe.

But, when the field collapsed to it's zero energy state (thus releasing all the energy that eventually became matter) space continued to expand. Why? This almost feels like inertia but space itself doesn't have inertia (does it) and the energy/matter in space would be at rest as it has nowhere to go. So why did the expansion continue?

I realize that now (12 billion years later) dark energy is starting to dominate and cause the expansion to speed up but what happened in the first few billion years when the matter and energy should have been pulling on space and causing it to contract?

@Ethan -- following your Comments of the Week #62, I would find an overview of the different quantum gravity options extremely educational! Please consider this a "Yes" vote :-)

I understand that the more dense gas clouds collapse to form the largest stars, and that the larger the star, the more short-lived its life.

My question is how, then, are there still areas that produce massive stars? Are there areas in galaxies that are super dense but have yet to collapse? That seems unlikely. Are they remnants of past supernovae? That doesn't seem like there would be enough dust.

What am I missing?

I wrote up the answer to the weighing puzzle for any number of coins (or men on an island), see http://camoo.freeshell.org/coin_weighing_puzzle.pdf

(1) Does the strong nuclear force cause an attraction between neutrons? (2) A free neutron has a 12-minute half-life. What prevents neutron decay in an atomic nucleus?

Not sure if the form submission works, all I get is a re-direct message:

Dear Ethan,

What comprises the "empty space" outside the nucleus of an atom? If atoms are >99.9% empty space, what exactly is that 'space'? Is it a vacuum? Is it strictly made up of energy inherent to space itself a.k.a. dark energy? Or is it something else entirely?

It's space like the stuff separating out the stars. The only difference is that it is very close to the constituents of the atom. It is definitely not anything special or unique.

Dear Ethan,

This is more of a thought than a question but I find it quite entertaining, so here it goes:

Assuming the inherent danger of the contact with a more advanced civilization (I think Steve Hawking has touched on this idea before) and adding to this the speculation from your article would lead to a rather unsettling conclusion: once the thermonuclear power technology is reached that would essentially set off the doomsday clock to the first encounter whether we like it or not. Since the signal is limited by the speed of light it would probably take many centuries until it finally leads to the detection by other neighboring civilizations. The history teaches us that short interest and greed (certainly so, compared to human life span) always prevails over any other consideration so I'm quite pessimistic that any esoteric argument such as staying stealthy in the interest of the security of longer non-discovery by others will be respected UNLESS the technology of "eternal life" (the means of achieving that are still debatable, whether through AI, uploadable consciousness etc.) is developed first!

To sum it up: as a civilization, we must first mature to the status of continuous consciousness (through "eternal life" technologies etc.) and only THEN indulge (or not) in the use of the controlled thermonuclear synthesis power generation, even though the latter may be achievable earlier technologically than the former! We may need to stand the temptation of virtually free power generation for the sake of self-preservation!

Dear Ethan,

About the Forbes article (http://www.forbes.com/sites/startswithabang/2016/01/02/ask-ethan-is-int…), you mentioned something about special relativity; that a long journey would actually take the traveler less time (20-30 years) because they are traveling close to the speed of light and their time slows down. I am not sure I understand this, does not sound right to me.

From the earths perspective, it is true that the time will slow down on the ship. But from within the ship's perspective, time does not slow dows. It does not appear any different. Actually, from the ship's perspective, time appears to slow down for earth instead. The twin paradox is resolved only when the ship returns and the two me up again to corroborate the information; the ship firing the rockets the other way breaks the symmetry and decides who is actually older when they meet again (since the retuning ships now travels faster wrt the original inertial reference frame to 'catchup' to earth that had appeared to be traveling away from the ship prior to the return trip). But as for the travelers themselves, it's still the same distance covered and the same velocity travelled. How can it take only 20-40 years (that would imply traveling faster than light wrt the ship's reference frame). Space contraction will not help here, So for the traveler, it would still take the generations to reach the star. Would it not?

My opinion, size is infinite. God's sneeze is our multi-universe. Our sneeze is a multi-universe, and so on. Unprovable but it's my theory.

But what does your opinion have to it other than a complete ass-pull of assertions?

Sorry, Wow, should have been more specific : Planck era is the earliest period of time in the history of the universe, from zero to approximately 10−43 seconds (Planck time). While there is no proven theory that correctly describes the universe at this period, it is postulated that quantum effects of gravity dominated physical interactions due to the small scale of the universe. During this period, approximately 13.79 billion years ago, gravitation is believed to have been as strong as the other fundamental forces, and all the forces may have been unified. Inconceivably hot and dense, the state of the universe during the Planck epoch was unstable. As it expanded and cooled, the familiar manifestations of the fundamental forces arose through a process known as symmetry breaking.
Modern cosmology now suggests that the Planck epoch may have inaugurated a period of unification, known as the grand unification epoch, and that symmetry breaking then quickly led to the era of cosmic inflation, the Inflationary epoch, during In the context of time, an order of magnitude is a description of the quantity of a time in respect to comparison between differing magnitudes. In common usage, the scale is usually the base10 or base−10 exponent being applied to an amount, making the order of magnitude 10 times greater or smaller.[1] As the differences are measured in factors of 10, a logarithmic scale is applied. In terms of time, the relationship between the smallest limit of time, the Planck time, and the next order of magnitude larger is 10. which the universe greatly expanded in scale over a very short period of time.[1]

"should have been more specific "

The following claims you made are completely different from the claim you'd made earlier.

Did you find more to pull out of your arse?

"The following claims you made are completely different from the claim you’d made earlier."

Which is WHY Tim prefaced the next post apologetically: "SORRY, Wow, should have been more specific"

Check.

You then proceed to insult a visitor/patron to Ethans blog:
"Did you find more to pull out of your arse?"

Checkmate:
Thus proving you are an assclown. Or perhaps I should say arseclown.

"Which is WHY Tim prefaced the next post apologetically"

Which wasn't clarifying the previous post AT ALL, and was another complete load of vomited ass-gravy unconnected with a working human brain.

Therefore was not a valid statement.

Dear Ethan,
I have a question about holographic principle. It says that all information that could contain in some volume of space is equivalent to the information that contain in sphere surrounding that space. Maximum information contains in black holes and sphere area of black holes is proportional to their mass^2. So we could take many tiny black holes and place them into some volume of space. Theoretically, in space with radius equal 10, volume equal 4186 and area of surrounding it sphere - 1256 we could place about 1000 black holes with radius equal 1. Total area (and information that contains in them) of this black holes is about 12560 (ten times more than area of sphere contained these black holes). I understand that after millisecond all these tiny black holes will merge into one big black hole, but for a small time we destroy the holographic principle, isn't it?

Dear Ethan,
I wonder, if photon happens to be on the black hole's event horizon, and the hole is vaporizing, with its radius reducing, is it possible that at some moment the photon will be located outside of the event horizon and consequentally escape the black hole?

P.S. I don't know if someone already mentioned, but your officially-Ethan-approved-way-to-contact form does not work ;)

"Scientists often state that they do not know what time is, but know how to measure it accurately, which is an oxymora."

Nope, not at all.

You don't know how children are born, but you can procreate.

Though I'm assuming here...

Dear Ethan,

I've read recent stories about asteroids that share the Earth's orbit (2016 HO3, 2003 YN107). Does that mean Earth is a dwarf planet?

If so, for the sake of Earth's status as a real planet, do you support an urgent global effort to remove these from our orbit? I know I do.

Dear Ethan,

The speed of the universe's expansion is less then the speed of light. What happens to a photon, emitted towards the boundaries of the universe?

Thank you!
Vadim Efimov

@Vadim Efimov #39: The expansion speed depends on how far away you are from whatever you're observing: the _rate_ is expressed as "speed per unit distance" (73 km/s per megaparsec). If the total distance is large enough, the observed rate of expansion (separation between observer and observed) can exceed the speed of light.

What happens to an emitted photon is that it gets stretched out (redshifted) according to that expansion.

The easiest way to do the calculation is to use the speed part of the rate and integrate it until the separation distance has increased from whatever you started at (say, one megaparsec) to some larger value (say, two megaparsecs), the ratio between the two tells you exactly the ratio by which a photon will have had its wavelength stretched during that same time period.

I wonder if you might be willing to do a narrowly-focussed astrophysics "explaining" post, rather than your usual wide-ranging, fate-of-the-universe (and YEC-baiting :-) ) pieces. I ran across two competing preprints in the astro-ph arXiv: http://arxiv.org/abs/1606.09024 and http://arxiv.org/abs/1606.09025.

I think I understand what the various authors mean by a "supernova impostor," but it would be really cool to get a slightly non-technical explanation of Luminous Blue Variables (surely that's *someone's* band name?!?) vs. Wolf-Rayet stars, and maybe some perspective on the really cool timescale these papers talk about -- apparently significant stellar evolution over the course of just years or decades.

Ethan, you may not know this, but the "I have a question" Web form at the top of this post no longer works. The form submits to "www.startswithabang.com" (predating your move to Science Blogs?), and then generates an error page "Sorry I can't send to ethan@startswithabang.com. Is ethan@startswithabang.com on this server?"

Dear Ethan,

Would it be possible to investigate following assumptions:
1. The space-time has a mass itself
2. The dark matter we are looking for, is not the matter but the space-time itself

Do we have any possibilities/tools/frameworks to investigate those assumptions ? Assuming that they have a sense in a first place.

My question is emerged from problems with understanding of virtual particles those are born and annihilate (for the most part) in vacuum. How oft are they born ? How fast are they annihilate ? Are they represent a significant mass in specific volume of the universe in their lifetime ?
Is there specific amount of energy we can associate to a virtual particles for their life-time ? I understand that sum of the energies of emerging and annihilating is equal to 0, but what about a time slice when those particles already born and not yet annihilated ?

I hope my question is not stupid enough to be ignored.
With best regards,
Pavel.

What is the Universe in a range below the very low frequency?

It's a third of the way to misty mountains, Alek.

"I’ve read recent stories about asteroids that share the Earth’s orbit (2016 HO3, 2003 YN107). Does that mean Earth is a dwarf planet?"

No.

Check the definition, dearie.

How to take into account the asteroid belt between Mars and Jupiter , Pluto 's orbit after the analysis of the microwave radiation and the red shift ?

In The Big Bang theory young universe expanded very quickly (cosmic inflation).
After some time inflation stopped.
Did speed changed because of the dark energy?
I mean that in young universe there was much dark energy and the universe inflated.
At some time almost all dark energy (suddenly) disappeared and inflation stopped.

Hello, Ethan!
What will happens, when the observer's event horizon, formed by space expansion rate, will be less, than a Planck distance?
Thank you!

Strangely, in the video, "Illustris Simulation: Most detailed simulation of our Universe," (nice music by the way), it says nothing about how many billions of years ago the sound track started.