Recently, a discussion started in one of my comment threads about whether the Big Bang was necessarily valid or not, and whether there were any reasonable alternatives. The answer is that not only is the Big Bang the best theory to explain the start and evolution of the Universe, it's the only one that
This all started in the late 1920s, when we realized that spiral nebulae were not just galaxies, but that these other galaxies were nearly all moving away from us. Moreover, the ones that were farther away from us were moving away faster than the ones that were nearer to us. This lead us to the picture that the Universe was expanding, like so:
After a little bit of math to go along with this, we quickly realized that the Universe is acting much like the Earth would if you had detonated a huge bomb at the center:
In this example, pieces of the Earth would be flying apart from each other, but Gravity would be struggling to pull the pieces back together. So it is with the Universe: galaxies are flying apart from one another, but Gravity is trying to pull them back together. This means that the expansion is slowing down as the Universe gets older, a hugely important discovery.
The reason I say this is important is because if the Universe is expanding and the rate of expansion is slower in the future, that means the expansion was faster in the past! It means that, billions of years ago, galaxies were much closer together to one another than they are today. It means that, over 13 billion years ago, all the matter in the Universe was bunched together at higher and higher densities. If you extrapolate all the way back to the entire Universe being in a single location with a nearly infinite density, before it expanded into what it is now, what do you get?
Well, folks, that's the idea of the Big Bang. Now, there are other possible implications for the Hubble expansion of the Universe, not all of which result in a Big Bang. But let's imagine the Big Bang were correct; what else would happen? Well, if we look at the Universe when it was early enough, it would also be denser and hotter. In fact, we can go back so far, when the Universe was only a few hundred thousand years old, to when it was too hot for neutral Hydrogen! We can recreate this in labs, and it's known as plasma:
Well, when this plasma finally cools enough (due to the Universe's expansion), it ought to emit light, and allow all the light left over from the big bang to simply move through the space of the expanding Universe until it reaches our eyes. But, that light wouldn't be UV light or visible light anymore. After 13 billion years of expansion, that light ought to only be a weak signal peaked at a temperature of only a few Kelvin. And it ought to be everywhere on the entire sky, nearly exactly the same in all directions, and it ought to fluctuate on timescales so slow that we'll never live to see it. The data from the result of this search?
Oh, was it momentous when we discovered this! The graphical depiction of the temperature of this leftover radiation on the sky looks like this:
But there's more. You see, we can extrapolate all the way back -- not just before neutral atoms -- to when it was so hot and dense that individual nuclei couldn't exist! Well, when the Universe finally cools enough so that they can exist, there should exist a certain number of neutrons, protons, and photons. We can predict how old the Universe is when this critical cooling occurs, and we find that the abundances of Deuterium (one proton and one neutron), Helium-3 (two protons and one neutron), Helium-4 (two protons and two neutrons), and Lithium-7 (three protons and four neutrons) are all highly dependent on one parameter: the ratio of photons to nucleons. In other words, we get four separate predictions for elemental abundances from the Big Bang theory. Then, we go out and measure these abundances, and see if they match up. The results?
They all -- to within reasonable errors -- match up as well. And the combination of these three observations, which are in strong agreement with what the Big Bang predicts, are why we subscribe to this theory so strongly.
Like I said, there are plenty of other explanation for just the Hubble expansion of the Universe. The problem is, none of them also explain the Cosmic Microwave Background and the abundance of the lightest elements. If you'd like to know about the many alternative explanations, I recommend reading Chapter 7 of this book, which goes through each possibility and why it's discredited. But the Big Bang isn't the final theory of the Universe, it's just a step along the way, as it's already been expanded upon. But, for what it is, it isn't just the best theory we've got. It's a great one.
Enjoy your weekend, everyone!
Physical Science
Comments
"...expansion is slower in the future, that means the expansion was faster in the past!"
Just to prevent confusion (which I suffered on my first read-through) this does not mean that the current rate of expansion is not accelerating.
Posted by: sean hogge | August 21, 2009 7:52 AM
Sean bet me to it.
Maybe I missed the explanation for this?
Is the universe going through "phases" of expansion rates?
The expansion was accelerating, then gravity kicked in and it slowed down and now it's accelerating again?
Posted by: Kevin K | August 21, 2009 8:53 AM
Ethan, in light of what you write, can you to comment on this http://www.space.com/scienceastronomy/090819-gravitational-waves.html article, which puts up the possibility to in the near future show a real flaw in General Relativity experimentally.
Would that allow to "resimplify" the standard model to get rid of the need for dark matter, inflation and/or dark energy? Or would a failure of GR invalidate the whole model (not the big bang per se from what you said, since that's an observed fact, or, at least the hot dense plasma universe is).
Posted by: Mu | August 21, 2009 9:00 AM
I can't remember when/how I stumbled upon this blog, but I am so grateful that I did. Thanks Ethan for another great post!
Posted by: Brian | August 21, 2009 10:38 AM
@kevin
Of course, there is the dark energy model which is accelerating the universe in the current state because this energy's density remains the same even if the space in between is getting larger. Dark energy concept was created after observing irregularities in the supernova:http://en.wikipedia.org/wiki/Dark_energy
It is an explanatory device, and it fits data, so I guess it exists?
Posted by: IBY | August 21, 2009 11:08 AM
I'll be long dead by then, but I hope that some day we'll have IceCube observatories whereever possible in the Solarsystem so that we can detect the primordial neutrino background. (I stole the idea from one of the 365 Days of Astronomy podcasts.)
Posted by: Sili | August 21, 2009 12:20 PM
Hey everyone! First off -- about the acceleration. The Hubble Rate is not accelerating. What it is doing is it's staying positive, and not dropping as the Universe expands. So, it should asymptote to about 60 km/s/Mpc. Which means that something 10 Mpc away will expand away at 600 km/s, but a few billion years later, it will be expanding away at 1200 km/s, and then at 2400 km/s an equal time later, and at 4800 km/s an equal time later, and 9600 km/s an equal time later. That's how the acceleration works.
The expansion, as far as we can measure, started out extremely large, slowed down, and now is ceasing to slow down.
Mu, Advanced LIGO should detect gravitational waves. If it runs for 10 years and doesn't, we've discovered new physics. If it runs for 10 years and does, we've directly detected gravitational waves for the first time. Either way, we win.
Sili, the primordial neutrino background is one of the greatest untested predictions of the big bang. A feasible way of detecting it would win its inventor a Nobel Prize, regardless of what the result was.
Posted by: Ethan Siegel | August 21, 2009 3:46 PM
There is a new theory that is challenging the current paradigm in physics which is Quantum Mechanics and String Theory. There is a new Theory of Everything Breakthrough. It exposes the flaws in both Quantum Theory and String Theory. Please Help us set the physics community back on the right course and prove that Einstein was right! Visit our site The Theory of Super Relativity: Super Relativity
Posted by: mmfiore | August 21, 2009 7:18 PM
Just want to say that I agree w/post #4 and keep up the great work Ethan. Your attempts to enlighten are very much appreciated. Any theories on pre-big bang universe? Where did this "infinitely dense matter" come from?
Posted by: Mike | August 21, 2009 7:19 PM
The explanation and grafts in this article ignore several points that are in direct contradiction to the Big Bang Theory.
For one, it ignores the point that the universe is apparently flat meaning in every direction we look it appears the same and the light appears to arrive in a straight line.
It also ignores the "inflationary period" needed to explain this apparently flat universe.
It claims the CMR is evidence of the Big Bang Theory,
it actually proves the universe is the same, "slightly lumpy" in every direction(flat). This could also be considered proof of a infinite steady state recycling universe.
If one looks at the Big Bang Theory with an open mind you will see there is only on fact that supports the Big Bang Theory and that is the red-shifting of light the further we look back into time. There may be another explanation for this red-shifting other than "tired light".
Viewing light as "waves of particles" instead of just wave or photons might explain the red-shifting of distant light.
Page 15 at this link gives another possible explanation.
http://www.scribd.com/doc/16251160/An-Alternative-to-the-Standard-Model-of-Physics
Posted by: Question? | August 22, 2009 8:17 AM
Question?,
The Big Bang does not dictate the curvature of space. It allows for many possibilities, including a flat Universe. Inflation is a compelling add-on to the Big Bang, as it gives you a flat Universe with the same temperature everywhere, that is also hot, dense, and expanding, with the correct spectrum of initial fluctuations that are consistent with our observations.
The discovery of the Cosmic Microwave Background led, immediately, to the abandonment of all serious steady-state models and the acceptance of the Big Bang. Why? Because steady state models, in addition to needing a matter creation field (in violation of the conservation of energy), now needed to explain this "fog" as well. How do they do it? They say, "infinite, recycling, steady-state Universe with matter creation." The matter creation contradicts our observations, the steady state contradicts our observations, and the infinite and recycling parts are purely philosophical, as they are immune to observations. The alternative to explain those things? Big Bang. And the steady-state model still won't give you deuterium or lithium-7.
The link you provide has numerous mistakes in basic (undergraduate-level) physics, and is not a reasonable theory.
Posted by: Ethan Siegel | August 22, 2009 8:53 AM
Ethan Siegel, you are missing the main point made in the theory of a steady state recycling universe. The universe is not expanding, the expansion is an illusion. There is no need for any "matter creation" to fill the expansion.
You mention deuterium and lithium-7, that can easily be explained (too long for here though, but you do not mention that the hydrogen-helium ratio is the same as it was shortly after the Big Bang. How can that be?
There are also problems explaining how such large structures as galaxy cluster could form in the short 14 billion year history since the Big Bang.
You mention the inflationary period (which violates the laws of physics) as a compelling add on. What's to say matter arose everywhere and the Big Bang and the inflationary period never happened?
Posted by: Question? | August 23, 2009 1:01 PM
@#12
Please do explain how the expansion of the universe is just an illusion and how the inflationary period violates the laws of physics. That link you cited just uses a bunch of fancy vocabulary without citing any evidence. Its just claim after claim after claim without any reason to believe a word of it. Hate to say it to ya, but you've been hoodwinked.
Posted by: erik | August 23, 2009 5:52 PM
Erik, and you believers in the Big Bang haven't been hoodwinked? The conclusion of an illusion (there is a test proposed which could offer some proof) is from the step by step logic without violating the laws of classical physics. The Big Bang violates the laws of physics because in the inflationary period the universe expanded at millions of times the velocity of light in all directions.
Posted by: Question? | August 24, 2009 6:03 AM
Questions?: do you have any formal education in physics (or mathematics, or, anything?)
Posted by: dean | August 24, 2009 7:12 AM
Question,
The idea that the expansion of the Universe -- supported by literally millions of independent observations -- is an illusion would require extraordinary evidence. There is, as far as I know, absolutely no evidence for it right now. Until you provide some, there is no way I'm going to tell any of these good people that there's a problem with the Big Bang. Indeed, there hasn't been a major one since the 1960s.
I'm not saying the big bang couldn't be wrong, but putting the pieces together from the evidence we have leads to the big bang and nothing else. I've already explained how the expansion of space doesn't violate special relativity, so don't sweat inflation.
Posted by: Ethan Siegel | August 24, 2009 7:34 AM
Ethan, I'm rooting for new physics, or even just finally stabilizing the current one. By my guess I've got about 10 years until I've to explain all this to a high school teenager. I'd love to only say anything with some form of authority, that won't be described as "man, my dad used to tell me that nonsense" when he's in college.
Posted by: Mu | August 24, 2009 9:27 AM
The problem with the Big Bang that I never see discussed as if it has been decided already and "everyone knows" the answer, is the black hole problem. IF all the matter in the Universe was gathered at one point, that would be one hell of a black hole. Since the only way to escape a black hole is to exceed the speed of light, all the matter in the Big Bang must have been accelerated by the infinite energy required to escape such a black hole. I have never heard an adequate explanation of how that happened when we are told all the time that black holes can only evaporate by quantum evaporation and that, otherwise, NOTHING can exit a black hole.
Hopefully I'll remember to check back in here for the answer.
Posted by: Oldfart | August 25, 2009 7:19 PM
Currently, the Big Bang theory seems to be the most sensible explanation about the known universe; it has its flaws,but at default of a better cosmological theory,the Big Bang remains the king for now.
The universe is expanding.If the galaxies are receding from each other but at a slower rate than in the past, this implies that the initial energy that propels the expansion of the universe is decreasing or cooling off because matter is progressively lose its density.The universe might reach a threshold where gravity will cause it to returns to its initials singularity and restart the process like a yo-yo if it is a closed system.
Posted by: Pierre F. Lherisson | August 27, 2009 11:09 PM
@Oldfart:
"IF all the matter in the Universe was gathered at one point, that would be one hell of a black hole."
If all the mass in the universe was gathered in one point which is part of a surrounding space, then you'd indeed have a Black Hole. But that has little to do with the Big Bang: at the Big Bang, all of the existing space *was* that one point, there was no surrounding space. Therefore this wasn't a Black Hole. (more mathematical: a Black Hole is described by a Schwartzschild metric, whereas the universe is described by a Robertson-Walker metric - different things...)
Posted by: Bjoern | August 28, 2009 6:54 AM
Ah. I got the scam now. It wasn't really a black hole because.....space and time hadn't been created yet.....by.....what? Something exploded ... If nothing yet existed, WHAT exploded?
Posted by: Oldfart | August 28, 2009 4:10 PM
Meanwhile...I will go look up Schwartzschild metric and Robertson-Walker metric....
Posted by: Oldfart | August 28, 2009 4:12 PM
Not that I understand either metric very well... I still have to point out that, by your comments, neither metric applied in the femto-second before the Big Bang. Two femto-seconds later the universe existed. I have no idea what the radius of the universe was after a femto-second but I'm pretty sure it was less than the Schwartzchild radius for that amount of mass. So, the universe blinked into existence and immediately was swallowed by itself....
Posted by: Oldfart | August 28, 2009 5:54 PM
I have heard that the Big Bang theory needs a Dark Matter factor to remain plausible. To date, no evidence of 'Dark Matter" has been found. Can someone please explain this issue to me in layman's terms? Also, the Big Bang theory says nothing about what happened before everything supposedly existed in one point. How did the mass of the universe get into such a small point in the first place?
And what happens to matter/energy that is sucked into black holes? We have no idea and maybe this has grave implications for how the current incarnation of our universe started.
I suspect that we are just babies when it comes to these theories and that the reality is much grander and more complicated than we know. But there is no insult in that, we have to start somewhere. A universe that just expands until the lights go out (unless of course there is the invented "Dark Matter" to pull everything back together) flies in the face of common sense.
Just the musings of a layman. Thanks for any clarifications.
Posted by: Richards Lapsa | September 7, 2009 1:27 AM
Richards Lapsa wrote
Two words: gravitational lensing.Posted by: RBH | September 18, 2009 8:35 PM
Of course James Peebles does agree that, "Our best efforts to explain the wealth of data are imbedded in a theory known as the standard cosmological model or the big bang theory." But that does not mean that everyone agrees that this model doesn't have enormous problems. From the beginning, Hubble was uneasy, "red-shifts may be expressed on a scale of velocities as a matter of convenience. They behave as velocity-shifts behave and they are very simply represented on the same familiar scale, regardless of ultimate interpretation. The term "apparent velocity" may be used in carefully considered statements, and the adjective always implied where it is omitted in general usage." And even today, there is reluctance in accepting the big bangs many necessary extraordinary hypotheses of the big bang theory. For example, Roger Penrose says, "What reason is there to believe that such an inflationary picture of the universe is likely to be close to the truth? Despite its evident popularity, I wish to give my own reasons for casting considerable doubt on the entire idea!" Elsewhere, Penrose concludes quite unenthusiastically, "Nevertheless we are stuck with the big bang theory and that also seems untidy. But there appears to be no way out." Well I beg to differ, there is a way out. But I won't burden this blog with my theory which you can read in my book, A Critique of Pure Physics (It is fully readable online, page 30 to 44 click on the link on my name.) But for here, let me just suggest that the Big Bang theory has enormous problems and the assumptions necessary to keep the Big Bang theory intact keep getting more extraordinary. The Big Bang theory is the epicycle theory of our time and with enough epicycles (extraordinary assumptions e.g. like the inflationary hypothesis for one, accelerating dark matter for another) one can proof anything. Now the dogmatic intolerance that Galileo faced came from the Church, today the primary dogmatic pressure comes from subspecialty bias within Physics itself. Let me add a word about the CMB: the CMB only supports the Big Bang theory because we are stuck with the Big Bang theory. Once the Big Bang theory is removed then one of the many alternative interpretations of the CMB will become more credible. Well I've said enough. Read my book if you'd like to understand my alternative big picture story of physics (not the big bang).
Posted by: Thomas Neil Neubert | October 1, 2009 5:06 AM
This is contrary to observation. The Lambda-CDM model meant that the number of parameters (which aren't at all "assumptions") were minimized; it is AFAIU the parsimonious set among the rivals; while at the same time the number of predictions increased.
Pray tell what those "problems" are? So far there is consistency between predictions and observation, so there doesn't seem to be any problem at all. Which of course sucks if we want to get to the next step as Ethan says.
No argument there. :-D
Posted by: Torbjörn Larsson, OM | October 24, 2009 6:29 AM
i was wondering, if this body of matter existed at the beginning of the universe before the big bang and it was concentrated enough, wouldn't the gravitational strength exceed the speed of light?
Posted by: the architect | April 9, 2010 1:35 AM
Yes indeed, this would all be true if our Ideas which are encapsulated only within our limited human minds capabilities were exactly true and historically correct, however if only one incident, which we may never ever know about, occurred differently in the first instance of the event, what we know today will have created a totally different scenario and a different chain of historical events within the theory.
So I think someone ought to draw up a chart indicating the limitless variations that could possibly have taken place in the universe rather than base all our knowledge on one Idea without variation.
Posted by: Tony Barhoum | May 17, 2010 8:22 PM
Assalam O Alaikum(May peace and blessings of Allah(GOD) be upon you all)
I hope u guys have learned enough to understand how it all goes? All such facts have been foretold by ALLAH(GOD) through his last messenger HZT.Muhammad(May peace be upon him) in THE HOLY QUR'AN.
All of my brothers,read the HOLY QUR'AN and revert to ALLAH(GOD).
Ur well wishers
ALL Muslims.
Posted by: Asad | March 2, 2011 2:07 PM
Assalam O Alaikum(May peace and blessings of Allah(GOD) be upon you all)
I hope u guys have learned enough to understand how it all goes? All such facts have been foretold by ALLAH(GOD) through his last messenger HZT.Muhammad(May peace be upon him) in THE HOLY QUR'AN 1400 years ago.
All of my brothers,read the HOLY QUR'AN and revert to ALLAH(GOD).
Ur well wishers
ALL Muslims.
Posted by: Asad | March 2, 2011 2:09 PM
The Big Bang -v- The Big Doughnut Theory MkIII (Or what happens when a Big Doughnut Spins)
To be read following:
THE BIG DOUGHNUT THEORY MKII
(Or THE LONG SAUSAGE ROLL THEORY)
Now, those Sausage Rolls without their sausage
Their pastry long, and smooth and glossy
Described how there had never (EVER) been
The need for a
-
“BIG BANG”
-
To start this mess that we’re in
(THE UNIVERSE!)
-
In fact I can think of nothing much worse
Than a “BIG BANG” to start off a whole Universe!
-
Therefore, and in keeping with my original theory
(Regarding the general distribution of matter)
Without any need for a
“BIG BANG”
TO
SPLATTER'
-
Our cosmic dust into a great space
(That had waited how long?)
For this event to take place
I return to my doughnut
The original plan
(Remember the type with a hole, and no jam)
But to make it much clearer (ie the system we’re in)
I have added another element;
-
REVOLUTION (or SPIN)
-
For if our doughnut were of
-
“UNIVERSAL”
-
Proportions
In the form of a vacuum with matter within
-
(analogy DOUGH)
-
In view of it’s totally enormous
-
CIRCUMFERENCE
-
It’s speed could then vary
-
(IF IT WERE TO SPIN)
-
For when “Spun” on it’s axis at slow revolutions
It’s centre could seem to be totally still
Whilst an object attached to it’s outer circumference
Much faster than light might travel
-
UNTIL
-
The dough at it’s surface grew darker and darker
(Just like night)
As it's speed prevented the escape of all
-
LIGHT
-
I would then suggest that this may be the answer
For the reason there exists such a mass of
-
“DARK MATTER”
-
Though
It
Does not result from ANY
-
“BIG SPLATTER”
-
But merely because;
-
WHEN A BIG DOUGHNUT SPINS
-
Light cannot escape
-
SO SOME BITS GO DIM !
-
So you see
(Although on the EDGE you will not)
-
POSITION
-
Determines our SPEED in this plot
And as SPEED is as TIME
(Just in case you’d forgot)
The “SPIN” is the reason;
WE ARE
and
NOT NOT!
-
Egal Bohen
March 2008
Posted by: Egal Bohen | May 10, 2011 4:31 PM
The pictures on this blog post are captivating. I don't believe in the big bang theory, it's garbage.
Posted by: pioneer vsx-1020-k | June 1, 2011 10:30 AM
@Ethan-'...the ones that were farther away from us were moving away faster than the ones that were nearer to us. This lead us to the picture that the Universe was expanding...'
But of course. Just as it may collapse in the future, like the swarm of the bees. 33Pioneer is right. Big Bang is gibberish.
Posted by: Andres Minas | August 29, 2011 2:34 AM