Big Bang, Big Bewilderment

Johannes Koelman

We live in an expanding universe. Distant galaxies move away from us, and these galaxies see us moving away from them. If we reverse time and trace back this expansion, it follows that the universe has evolved from a dense primeval/primordial state.

The big bang concept summarized in three sentences.

Sounds easy?

History shows that the concept of a big bang is difficult to swallow. That even holds for the brightest minds in the history of science. For thousands of years, mankind has struggled with the basic question “Does the universe have a beginning?” In hindsight, the answer was up for grabs more than three centuries ago.

Missed opportunities

When Isaac Newton discovered the law of motion and gravity, he struggled with the fact that these laws render the universe unstable. Celestial bodies behave no different than an apple close to earth. Material bodies do not remain in a stable separated configuration just like an apple does not float above earth. Inevitably, the earth and an apple will collapse together, and so will the celestial bodies that make up the universe.

Newton''s apple Newton could have argued that his laws are time-reversible, and that a reversal of a collapse would yield an expanding universe that is fully compatible with his laws of physics. He could even have concluded that three different models for a dynamical universe are possible: 1) a universe that expands forever (the reversal of an apple hitting the earth like a meteor), 2) a universe that undergoes an expansion followed by a contraction (the reversal of an apple thrown in the air with velocity below escape velocity), and 3) the in-between scenario in which the universe decelerates but never contracts (the reversal of an apple falling to earth starting from a standstill at infinity).

More than two centuries later, another true giant in science had an even better chance to predict an expanding universe, but also blew it. Even worse, when Albert Einstein discovered that his theory of gravity did not allow for a stable universe, he started tweaking his equations. Even for a scientist as bold as Einstein, a big bang universe was a too far-fetched concept.

Accepting the big bang

Key is that both Newton and Einstein lacked direct observational evidence for a cosmic expansion. Apparently, without such hard evidence it is virtually impossible to consider a cosmic expansion. And even with such evidence, acceptance of a big bang cosmology is far from a done deal. In 1929 Edwin Hubble made the discovery that distant galaxies move away from each other with velocities proportional to their distance. Yet, it took many tens of years and the observation of a true relic of the big bang (the cosmic microwave background) in the 1960's, to get the big bang widely accepted as the standard cosmological model.

If the brightest minds have wrestled many years with the concept of an expanding universe, who can blame a lay person struggling to accept the big bang? To make things worse, the treatment of cosmic expansion in the popscience literature is confusing and often inconsistent or even misleading.

In his recent book 'From Eternity to Here', Sean Carroll makes the statement: “[..] of all the confusing aspects of modern cosmology, probably none has been the subject of more misleading or simply untrue statements [..] than the big bang”.

Five years ago, Scientific American ran an article with the title “Misconceptions about the Big Bang”. The authors of this article, Lineweaver and Davis, state: “Renowned physicists, authors of astronomy textbooks and prominent popularizers of science have made incorrect, misleading or easily misinterpreted statements about the expansion of the universe. Because expansion is the basis of the big bang model, these misunderstandings are fundamental.”

I agree with these sentiments. In fact, I consider it a small miracle that so many people seem to accept a concept as ill-explained and miscommunicated as the big bang.

Visualizing the big bang

How do you visualize the big bang? If I ask you to draw the big bang, would you attempt to draw an explosion similar to this?

A not entirely correct Big Bang

As a representation of the big bang, this picture is severely flawed. Imagining the big bang as an explosion originating at a specific location in space, represents a gross violation of the cosmological principle. This principle states that the universe has no preferred location, nor a preferred direction. You can think of the cosmological principle as nothing more than the Copernican debunking of geocentrism driven to its ultimate consequence: from a cosmological perspective our place in the universe is not special, and neither is any other places. Therefore the big bang did not happen at a particular place. It happened everywhere. The big bang represents a temporal singularity rather than a singularity in space.

Can we create a visualization of the big bang that is understandable, yet honors the key physics? Key challenge for any big bang visualization is that in some way it needs to translate Einstein's laws of general relativity, which dictate the cosmic expansion in terms of metrical spaces, into a more easily understandable kinematic description of galaxies flying apart. People can grasp an explosion of galaxies flying apart, but struggle with abstract mathematical concept like a Robertson-Walker metric.

Let's start with a uniform explosion in a one-dimensional space. It looks like this:

1-D universe

You can think of the dots representing galaxies flying apart. Each galaxy sees the others moving away, and galaxies at larger mutual distance move proportionally faster away from each other. This is exactly the expansion observed by Hubble.

There is a problem though. Galaxies that are further separated, recede from each other more rapidly, and beyond a certain distance, galaxies will fly apart faster than the speed of light. To correct this, we need to bring some relativistic concepts into the picture. First, we represent the one-dimensional galactic explosion in spacetime:

1-D explosion in space-time

Spatial separation is indicated horizontally, and time runs vertically. In this picture the slope of the galaxy trajectories represent their velocities (as observed from the galaxy in te center of the picture).

To render this picture relativistically correct, we need to 'bend' the trajectories such that the angle with the vertical (time) axis stays smaller than the angle corresponding to the speed of light. This bending corresponds to the well-known relativistic time dilation: time runs more slowly for fast moving objects. So we imagine that each of the galaxies carries a clock that started ticking at the moment of the big bang, and plot the positions of the galaxies when all galactic clocks show the same time. We get the following picture:

Relativistic 1-D explosion

Notice that the time indicated along the vertical axes is associated with the central galaxy in this picture. From the perspective of this central galaxy, galaxies further away move faster and their clocks tick slower, and therefore they reach a given position only when the clock of the central galaxy indicates a much later time. This causes the 'bending up' of the line of galaxies. By plotting all galaxies at synchronized proper (cosmological) times, we effectively have relativistically mixed space and time and created a curved space (yellow band) that stretches itself more straight with time:

Expanding space

Notice that in this picture the big bang (cosmic time zero) is represented by two straight lines: two opposing flashes of light filling whole space.

We are now ready to indicate the visible universe as seen from the galaxy central in the picture. These are nothing more than the rays of light traveling from the past and ending at the central dot. In a one-dimensional universe there are two such light rays, indicated by the green line segments in below figure. To render this visualization more complete, the early opaque phase of the universe (denoted in yellow) is distinguished from the transparent phase. The interface between the two represents the 'surface of last scatter'. This surface marks the visible depth of the universe. It is visible as the cosmic microwave background, the afterglow of the big bang discovered in 1964 and mapped out by the COBE and WMAP satellites.

Big Bang Model

Again: the Cosmological Principle

Ok, so if you want to imagine the big bang as some sort of explosion, the correct picture is shown above. It honors the theory of relativity, yet is a caricature of 'the real thing' as only one space dimension is represented, and the effects of gravity are ignored. Its qualitative features, however, are correct.

But wait a second. What about the cosmological principle? Surely this principle is grossly violated: the galaxy in the center of the picture surely occupies a very special place in this one-dimensional universe. Ptolemy would perhaps like this model, but Copernicus and Galilei certainly wouldn't.

Not too quick! This is where the magic of Einstein's theory of relativity comes into play. In the above picture the central galaxy seems special, but that is only so because we have represented the universe from the perspective of this particular galaxy. We can 'scroll' through this one-dimensional universe and experience a universe that looks the same from each alternative perspective:

Scrolling through the Big Bang

Clearly each galaxy occupies an equivalent position. Our one-dimensional model universe obeys the cosmological principle in the most detailed way possible. Each point in this universe is at the center of it. It is just a matter of perspective.

Also obvious from this picture is that the 'scrolling' can be continued indefinitely. This universe is truly infinite. However, from the perspective of each galaxy, the observable universe (the green light rays emanated from the surface of light scatter and illuminating the galaxy) is finite. Note, however, that different galaxies have different observable universes associated with them.

There is much more to be said about this model universe. But let me stop here, and ask you a concluding question: do you accept the big bang? Do you consider it a truth like you consider a non-flat earth a truth?

If not, have you ever wondered why the night is dark?

Comments

Big thumbs up! Thanks for the article.

Rycharde Manne | 02/25/10 | 04:03 AM

I learned about the Big Bang with the metaphor of spots on a balloon that is blown. All the spots see the others moving away with a speed that increases with distance.

This is a non-relativistic picture though. But I did not care a lot about the relativistic correction. I could believe that you would not see super-luminal speeds without all the fuss.

I know that one Dutch novelist, Harry Mulish, got it wrong completely and wrote about an astronomer who succeeded in seeing an image of the pre-bang universe (heaven+angels) reflected on galaxies. I never understood what kind of warped idea he had of astronomy.

Rob

Rob (not verified) | 02/25/10 | 07:57 AM

Great article. Also really liked the earlier one about entropy and gravity.

The line near the end where you wrote, "Note, however, that different galaxies have different observable universes associated with them." intrigued me the most.

I'm definitely a layman around this stuff, but that statement opens all sorts of questions for me.
I'm interpreting your statement as meaning that from the perspective is a galaxy most distantly visible to us, they would see a universe that included some of the same galaxies we see (where our respective light cones intersect), but they would also see a lot more that we could not. In turn the galaxies most distant from them (and further away from us) would have a view that included only galaxies that we can not see. etc etc etc.

Do you have any reason to expect that the same starting singularity applies equally to all of these perspectives or anything to suggest that there is any bounds to the progression of such perspectives?
i.e. Is this a case of the universe being infinite, but most of it being out of view due to limits on light speed?

Andrew Downing (not verified) | 02/25/10 | 08:48 AM

Thanks Andrew.

What this model highlights, is that the term 'observable universe' is subjective (observer dependent). We do not know whether or not the total universe is infinite. All the current cosmological hard data we have, certainly is compatible with an infinite universe. Yet, the total universe could be finite, but it has to be at least many times the size of our observable universe.

So it is definitely true that,most of the universe is out of view.

Johannes Koelman | 02/25/10 | 21:26 PM

"Newton could have argued that ..."

Newton was much too smart for that. Big bang model relies on great many assumptions many of them experimentally untestable and therefore unscientific. The main problematic assumption is that we already have all the relevant knowledge needed to understand past evolution of the Universe. This assumption is unacceptable to anyone who is well aware of not only what is known but also of what is still unknown, the letter trumps the former.

As long as there are huge gaps in our understanding - by which I mean things like dark energy, dark matter (we cannot explain 95% mass-energy content of the universe ffs!), inflation, inability to reconcile quantum mechanics with general relativity, lack of explanation of countless parameters of SM, lack of mathematically rigorous theory of matter, etc, etc - those who make grandiose statements about the beginning of the Universe are either very naive or very dishonest. Luckily for us not much depends on such predictions being correct but let me tell you if the life of your family depended on their correctness you would certainly be much more skeptical about modern cosmology.

For example the expansion of the universe is mostly based on redshift, which is though to result from expansion of space, but there is no experimental evidence for that phenomenon. Besides there is another just as valid explanation - that redshift is an intrinsic property of all electromagnetic radiation. This possibility has never been ruled out experimentally due to obvious technical problems. The only arguments against it are based on our ignorance - we don't know how it could work, but that doesn't prove anything, besides we don't know how dark energy works either.

Another example is the assumption that law of physics which hold here and now can be generalized to everywhere and all time - this is a breathtaking generalization based on very little evidence.

Science is based on a scientific method which in turn is based on experimentation and this is where all the power of science comes from. Scientific knowledge is only as solid as the experiments which back it up, unfortunately in cosmology only a very limited experimentation is possible which makes the knowledge acquired much more questionable then in other fields of natural science - it's worth keeping in mind.

P (not verified) | 02/25/10 | 12:35 PM

As a layman, I have to admit that I was not aware of all the problems that you presented, but I would like to propose a flaws in one of your arguments. Concerning redshifts, they do not directly say anything about an expanding universe. Redshifts are considered as an example of Doppler shifts which would lead to the conclusion that galaxies are moving away from one another. There are various reasons why redshifts are considered to be a Doppler effect, and I think the most convincing of this is the argument that if this wasn't the case, then every galaxy would have its own physics.

Although I realise that you consider this to be a possibility, it is highly unlikely. Consider for instance a galaxy very similar in structure, age and composition to our own. It turns out that the spectra of such galaxies are almost exactly like our own except that it is shifted a bit to the red spectrum. If the Doppler effect couldn't count for this, we would have to conclude that star formations in each galaxy had its own unique properties, even if the starting material is the same - If hope this explains the flaw in your logic..

The alternative argument about redshifts you make is that they are an intrinsic property of EM radiation. I think this is the least convincing of all your statements, simply because if it is an intrinsic property of EM radiation, then blue-shifted galaxies wouldn't exist, but sadly - they do (Andromeda as well as others).

Either way - this proves nothing about expansion - only about movement of galaxies. The reason that redshifts support expansion is because of this: if there is no preferred direction of motion of galaxies, then there would be statistically equal examples of both red and blue shifts. This is not the case. The overwhelming majority of galaxies are redshifted i.e. moving away from us. This lends us towards the idea that since things are moving away from one another, it is likely that in the past they were closer together. These are all very sound physical and mathematical conclusions.

None of these ideas prove the big-bang. I think the biggest support of the big-bang is cosmic background radiation. It is unnecessary in the universe if the universe didn't expand from something similar to the big-bang.

The other problems that you mention are interesting, but I think flawed in that you do not really require a complete understanding of all aspects of a situation to draw conclusions about it. For example if you go past an accident and see skid marks on the road, you are safe to make the logical conclusion that someone lost control of his/her car which led to the accident. You do not need to know the mental state of the driver, or the status of the brakes of the car to make that conclusion - it is valid regardless.

Samshive (not verified) | 02/25/10 | 18:28 PM

By intrinsic redshift I mean some effect which would have the wavelength increase with distance - it would not lead to equal amount of blue-shift as distance can only be positive. Besides this effect would be in addition to normal gravitational and Doppler shift.

Yes, CMB does agree with Big Bang cosmology, but is that the only possible explanation? For example is there any experimental proof that CMB is really global and not local? We can only see it from one location at one time, perhaps it is a local background of our Galaxy produced by light on light scattering or some other as yet undiscovered process.

The problem with your skid-marks analogy is that accidents are very simple - the amount of possibilities is limited so you can quickly rule out most of them, in the case of the Universe we don't know what the possibilities are and so we cannot use simple elimination to conclude which explanation is right, there could be explanations we haven't discovered yet. In other words the fact that we cannot come up with better physical theories is not a proof that our current ones already capture everything.

That our present theories are not final should be obvious when one considers how poorly they work in some areas - we can only explain 5% of the mass-energy content of the Universe and have no idea what the other 95% is made of! This alone is more then enough to prove that our understanding of cosmology is inadequate and that our cosmological model do not deserve much confidence. But there are other problems, our two best theories or matter - Standard Model and General Relativity - cannot be reconciled; we are unable to calculate vacuum energy (it comes out absurdly high or infinite); we don't know where parameters used in our theories come from and why they have the values they have; we don't know if those parameters can change in time or from place to place, and so on and on, to put it another way our ignorance is simply immense and dwarfs our knowledge. Considering all this the confidence with which people proclaim that our Universe originated in the Big Bang is rather surprising.

What we need is a more humble attitude, like the one exemplified by Newton: "I was like a boy playing on the sea-shore, and diverting myself now and then finding a smoother pebble or a prettier shell than ordinary, whilst the great ocean of truth lay all undiscovered before me."

P (not verified) | 02/25/10 | 21:48 PM

OK, let me start of by saying that I am not convinced with your arguments about an intrinsic redshift based on distances. If that was the case, you would naturally be able to test that hypothesis. It really isn't as difficult as you suggest. A laser fired from 2 locations to the same observer should be able to detect it. If the shifts are so small as to be only visible on really large scales, then you still need to account for the lack of such observable evidence when viewing different stars within our own galaxies - the effect needs to be at least testable.

Regarding the background radiation, if it is a local phenomenon, you need to find a mechanism that allows our galaxy to emit such radiation while preventing other galaxies from doing so. I think such an explanation would be far too complicated and I think its far simpler to consider it the remnants of something akin to the big bang.

I do agree that the universe is complex, but when it comes to the question of universal expansion or lack thereof, there are only 3 options - stable, expanding or contracting. Of course, a cyclic model is also possible, but on a local scale this would be seen as either expansion or contraction. Currently the evidence points to expansion. Its that simple!

Also, I do not think that you quite understand the current model of cosmology - if you reject an expanding universe, then the problem with dark energy disappears - so think about it. Also there are explanations for Dark matter - look up MACHOs and WIMPs. There are reasons why both of them are difficult to detect, but to suggest that we have no idea of the mass-energy content, thats an oversimplification.

Regarding the other problems - you are suggesting, like you did before that not knowing everything disqualifies the theory completely. That is really not the case and the skid-mark analogy that I made earlier is still valid. What we know is reasonable - there is still lots we do not know - no one is suggesting otherwise. The other problem with your argument is that you are suggesting that lack of knowing the exact parameters involved in a theory makes the theory unusable. If science really worked that way - we would never have had any real progress in knowledge.

Oh, and one last thing - I really don't think Newton was a humble person - even his statement regarding "the shoulders of giants" was meant as a sarcastic remark. He was a great scientist, but arrogant, hard-headed and he even considered himself a prophet. So scientists modelling themselves on Newton might not be the ideal view that you are suggesting.

As a final statement, I do want to say that I do agree with you that the big bang might not be the answer, but it is the best explanation we have at the moment, and to simply say that its wrong without giving an alternate theory that is consistent with the available data is a pointless endeavor.

Samshive (not verified) | 02/26/10 | 14:32 PM

I really enjoyed your article, and I think that it explained the conceptual idea of the big bang quite well. That being said there are 2 main questions that I think really needs to be answered.

The first one is about baryogenesis. As a layman with a bit of knowledge about statistics, I just cannot wrap my head around the idea that matter should exist instead of antimatter (not my favourite term). If only Baryonic matter existed I think I could accept that more easily, but since both baryonic and antibaryonic matter can exist, it does beg the question about why one should exist over the other.

The second question, and I think more importantly, is the question of what exactly space is. I apologize if this question sounds ridiculous, but this is one thing that has puzzled me. For instance, if space is expanding, shouldn't everything physically expand with it. My notion is that if we already exist within space (including the space between particles in our bodies), and that space expands - in a closed system shouldn't we also expand with it, or is the notion of space excluded from closed systems. and if it is, is the universe really a closed system. I kind of find it arbitrary developing concepts such as the big bang and expanding universes without a proper definition of what exactly space is.

I would appreciate if you could help me with answers to these questions, and help me understand more about the universe.

Samshive (not verified) | 02/25/10 | 17:45 PM

You pose two very good questions:

1) where is the anti-matter? Why is there not a 50-50 distribution of matter and anti-matter in the universe?

Answer: various models and mechanisms are proposed to answer this question. Currently there is no consensus on what is the right answer. (See Wikipedia on baryogenesis.)

2) what is space? If space expands, why doesn't everything (including meter sticks) expand with it?

Answer: In many popscience books the cosmic expansion is represented by galaxies imagined to be glued on a giant balloon that gets inflated. In above blogpost, I have carefully avoided the whole idea of expansion of space. One of the reasons is to avoid this question! (A second reason is that this analogy gives rise to superluminal expansion, a third reason that this model tends to create aether-like construct in people's mind, and a fourth reason that this analogy makes people believe that the universe is expanding into some higher dimensional hyper-universe.)
For those who do want to understand the cosmic expansion in terms of an expansion of space: this expansion of space is most effective at large distances (interpreted as a repulsive force, it is proportional to distance). At short distances, it is not very strong. The cosmic expansion does cause galaxies to expand a bit, but it is not strong enough to pull them apart. And this expansion is certainly not strong enough to overcome electromagnetic forces that hold clusters of atoms and molecules (you, me and meter sticks) together.

Johannes Koelman | 02/25/10 | 21:53 PM

I would just like to add to Johannes' wonderful explanation concerning the expansion of space that the gravity of individual galaxies is more than enough to counteract any repulsive force responsible for the expansion of space. Even in between two or more galaxies in a cluster, the net effect is that gravity prevails. That is why the galaxies in the local group are moving towards each other, e.g. why M31 and the Milky Way will one day merge.

But, Johannes is absolutely correct. On a small scale this repulsive force is insignificant, especially when compared to much the stronger electromagnetic forces.

Eric Diaz | 02/26/10 | 13:52 PM

Johannes and Eric, I thank you for the explanations you have provided, but I still think the idea of space is quite vague - I am still looking for a more appropriate idea of it.

But regardless of that, there is one last thing about spacial expansion that I do not quite understand. Currently the rate of expansion of the universe is increasing, and to account for this scientists use the ambiguous term "Dark Energy." Intuitively for me, the energy required to expand something of size '2z' would be more than expanding something of size 'z'.

So at least to me this suggests that more and more energy is used for expansion. This goes against everything I've learnt about closed systems, and the universe is supposed to be the all-encompassing closed system. So my question is how do you take account of that.

I do kinda get what you say about the scale of forces involved, but let me just ask if you think that the rate of expansion of the universe would reach a point where the interacting particles of forces such as the electromagnetic and gravitational forces couldn't reach one another? If so what happens to the particles themselves - I find it hard to think that they just disappear.

Samshive (not verified) | 02/26/10 | 14:45 PM

Well, to be perfectly honest with you, there is a theory in cosmology that states that in time everything including atoms, protons, neutrons, quarks, etc. will be ripped apart by the accelerating expansion of the universe. The theory in fact is called the Big Rip! LOL

But it is just a theory and a highly controversial one at that. Mainstream scientists don't believe that this is what is really going to happen.....well, some do.

When things get this abstract and so far away from empirical verification, it's almost impossible to say which theory is correct and which theory is dead wrong. What can I say?

Eric Diaz | 02/26/10 | 15:20 PM

Newton could have argued that his laws are time-reversible, and that a reversal of a collapse would yield an expanding universe that is fully compatible with his laws of physics. He could even have concluded that three different models for a dynamical universe are possible: 1) a universe that expands forever (the reversal of an apple hitting the earth like a meteor), 2) a universe that undergoes an expansion followed by a contraction (the reversal of an apple thrown in the air with velocity below escape velocity), and 3) the in-between scenario in which the universe decelerates but never contracts (the reversal of an apple falling to earth starting from a standstill at infinity).

This particular example I have a problem with in the context in which you are presenting it, and I'll tell you why. True, during Newton's time the solar system and the stars were considered the entire universe. They weren't even aware that they were living in an "island universe" (i.e. a galaxy). But even if they had been, it wouldn't have made any difference to the argument.

The expansion of the universe and the stretching of space-time are moot points in our solar system and our galaxy since the gravity from the mass of each pretty much negates any stretching of space. The instability with which Newton was faced was of an entirely different nature. The instability of our solar system is due to perturbations due to tidal interactions between all of the bodies in it.

Now in all fairness to Newton even though he worked out his three laws of motion and by combining them with Kepler's three law of planetary motion worked out his law of universal gravitation, he did so using the calculus which he privately developed. But when he published his laws of motion and his law of universal gravitation in his seminal treatise, Philosophiae Naturalis Principia Mathematica or just The Principia for short, he did not present it in the calculus with which he had developed these laws, but rather in the more crude form of geometry which was not suitable for the subtleties of tidal perturbations. I know, because I own a copy of the Principia, and have read it from cover to cover.

It is also true that Newton didn't believe that there was a mathematical solution to the inherent instability of the complex tidal interactions in our solar system and simply attributed the apparent stability of it to the Divine. A cop-out? Probably! But the expansion of the universe would have had no relevance to this problem whatsoever.

Now it's true that Pierre-Simon, marquis de Laplace during the time of Napoleon did manage to work out a mathematical solution to the instability of our solar system. But here's the thing; it was all in vain. Why? Because recent Lagrange-Laplace (LL) secular theory has shown that, in the long term, all planetary systems are inherently unstable, including our own solar system. Eventually our solar system will become dynamically unstable, long before our sun becomes a red giant.

Now Einstein is an entirely different matter all together. His own theory of general relativity contained within it predictions that our universe was dynamic and either had to be expanding or contracting--something which he didn't realize at the time. It was pointed out to him by a colleague.

But in fairness to Einstein the prevailing idea at the time was that the Milky Way was the entire universe--this view spearheaded by Harlow Shapley of the Mount Wilson Observatory. This was the consensus at the time. Einstein was only going by what the astronomers were telling him that the empirical data was telling them. So as a consequence, he introduced the extraneous term to his equations, which we know as the cosmological constant, to make his dynamic universe stand still. It was only when Edwin Hubble and his then night assistant Milton Humason proved beyond a shadow of a doubt that the universe was expanding did Einstein realize that he had made a terrible mistake and that his theory in its original form was correct.

The irony of it all if you believe in the existence of dark energy, is that Einstein came to the right conclusion but for the wrong reasons based on a premise that was eventually proved wrong! If indeed dark energy is the cause for the acceleration of the expansion of the universe, then the cosmological constant is correct.

Other than that, Johannes I found your article to be extraordinary! : )

Eric Diaz | 02/25/10 | 20:08 PM

Hi Eric -- you are perfectly right: no-one can blame Newton that he didn't come up with the idea of an expanding universe. In fact, in light of the observational evidence at that time, it would have been silly if he would have done so.

It was not my intention to suggest that Newton should have concluded that the universe is dynamic, but rather that Newton's laws in itself are sufficient to come to this conclusion. (Several introductory text on cosmology incorrectly suggest that one needs Einstein's theory of gravity to understand the concept of cosmic expansion.) In fact, Newton's law of gravity can be used to derive the Friedmann equation that describes the cosmic expansion for flat space. Key is the effacing principle that was derived by... Newton himself. (A nice description of this can be found in Tony Zee's book 'An Old Man's Toy'.)

Einstein is indeed a different story. Already in 1912, Visto Slipher had measured redshifts of 'spiral nebulae' and found that these were receding with very high velocities (likely high enough to escape Milky Way's gravitational field). And in 1917 Heber Curtis discovered faint novae in spiral nebulae. All of this strongly suggests that the then-called 'island universe' model of the universe (with the milky way not being the whole universe, but an island in a larger universe) to be correct.

I agree that we can not blame Einstein for having decided to ignore all of this. The whole debate on whether the universe extended beyond the Milky Way was certinly controversial at the time when Einstein constructed his theory of gravity.

Johannes Koelman | 02/25/10 | 22:29 PM

Hi Johannes, That's an interesting point you make about Newton's laws. You could in fact conclude from his laws that the universe is expanding. If Newton had had, Edwin Hubble, Milton Humason, Heber Curtis of the Lick Observatory, Vesto Slipher of the Lowell Observatory, George Ellery Hale to build Mount Wilson Observatory, the 100" Hooker telescope and a little luck, Newton probably would have concluded that the universe was expanding. LOL ; )

Eric Diaz | 02/26/10 | 00:32 AM

It is also true that Newton didn't believe that there was a mathematical solution to the inherent instability of the complex tidal interactions in our solar system and simply attributed the apparent stability of it to the Divine.

Newton had no reason to assume the universe was more than 6000 years old. So there probably would not have been enough time for instabilities to build up. No need to tweak the formulas.

Only after Lyell and Darwin was it possible to conceive of a universe millions of years old. Only after Hubble and the discovery of stellar physics we get into the billions of years.

Rob

Rob (not verified) | 02/26/10 | 04:57 AM

Are we limited to just one bang? Could we not have, perhaps, a small bang within a big bang?

Anonymous (not verified) | 02/25/10 | 21:09 PM

A cosmic gangbang?

JocK (not verified) | 02/25/10 | 21:57 PM

It seems to me that one must wrap one's mind around infinity mathematics to even begin to understand what is happening in this Universe. We think in terms of a beginning and an end, of a start and stop, backwards and forward. In infinity mathematics, there is nowhere in the Universe that you can go and still be closer to infinity. The big bang theory is just another item to look at on our path of continuing evolution. I think that one day in the distant future, people will look back and laugh about a big bang theory. It's fun to think about it, but there's no solutions in it.

oicur12ok (not verified) | 02/26/10 | 10:50 AM

Quite an interesting article Johannes, but you didn't mention other dimensions, as mathematicians do.
I think it was the 26 August edition last year in New Scientist that discussed this.
Why do cosmologists have such a problem with other/more dimensions, whereas mathematicians don't?

Ralph (not verified) | 02/26/10 | 11:02 AM

There is a problem though. Galaxies that are further separated, recede from each other more rapidly, and beyond a certain distance, galaxies will fly apart faster than the speed of light. To correct this, we need to bring some relativistic concepts into the picture.

Johannes is absolutely correct about this. And this presents a problem for astronomers who work in extragalactic astronomy. The problem of course is that when you're measuring redshifts of galaxies billions of light years away from us you have to account for the relativistic effects that Johannes mentioned above. Otherwise you're going to end up with a distance that is considerably greater than the age of the universe, which of course is impossible, i.e you can't have a galaxy 21 billion light years away if the universe is only 13.7 billion years old. Well actually, you could have a galaxy 21 billion light years away from us, but you would not be able to see it, since it would have taken 21 billion years for the light from the galaxy to have reached us, and only 13.7 billion years have past since the Big Bang. So that galaxy would be outside the "visible" universe, and therefore out of our range of observation.

When measuring a Doppler shift of an object in our own galaxy where relativistic effects are not a concern and objects are moving through space as opposed to moving with space, the equation used is quite simple: Δλ/λ=v/c. In plain English, all this equation is saying is that the change of the wavelength of light as a result of moving toward or away from us in our line of sight divided by the initial wavelength of light when it was first emitted is equal to the velocity of the object, either towards or away from us, divided by the speed of light. And that will give you either the redshift, if the object is moving away from us or a blue shift, if the object is moving toward us.

If, however, you're measuring the redshift of a galaxy billions of light years away, then you have to account for relativistic effects in your equation and you end up with this: Δλ/λ=[(c+v)/(c-v)]^½-1 or z=[(c+v)/(c-v)]^½-1 where 'z' symbolizes redshift.

Eric Diaz | 02/26/10 | 14:36 PM

Hi Eric

I just want to point out a flaw with your statement - you can see galaxies that are currently further than 13.7 billion light years from us. The light just took 13.7 billion years to reach us. The reason for this is that the universe is expanding. Even if physically for the light particle, it took less than 13.7 billion years to reach us, the expansion of space would imply that the actual distance to the originating light source is significantly more.

The actual edge of the observable universe is about about 46 billion light years.

Samshive (not verified) | 02/26/10 | 15:04 PM

Thank you, Samshive. You are absolutely correct! I had forgotten about that. The edge of the observable universe is now located at about 46.5 billion light-years away from us. I'm still half asleep. I was up most of the night, so I'm not thinking clearly.

What I meant to say is that if you don't take into consideration relativistic effects when measuring redshifts of distant galaxies "the age" of the galaxies you are viewing is going to be off. In other words, the cosmological redshift tells you how old the light of the object that you're measuring is and thus what the object looked like at that particular time in the history of our universe.

Thank you for catching my error. Good catch, btw! ; )

Eric Diaz | 02/26/10 | 15:57 PM

If Big Bang is some kind of giant black hole?

And time as a curved space (yellow band) that stretches itself more straight with time: it will mean that time has an end. If the expansion accelerates it will mean time change; compare to subjective experience.

Ulla (not verified) | 02/26/10 | 15:29 PM

Thanks, Johannes, now we're all going to have to do little videos!

Very nice. I do note that ever-present Starbucks are consistent with the Cosmological Principle.

Mark Changizi | 02/26/10 | 16:52 PM

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