Is the Big Bang Theory a Foolhardy Extrapolation?

[marcus]

I admit that to a large extent I'm referring to the view of popular science journalism. That's because I always avoided cosmology while learning GR (shouldn't have done this, I guess).

Maybe I just haven't found an adequate attitude towards pop journalism yet. It's the same with my own field, theoretical particle physics (in which I consider myself a novice): Everywhere the public is informed about how fantastic the standard model is and how cool physicists are. But if you look more closely it boils down to some highly accurate predictions, some quite reasonable ones, and the bloody rest.

It sounds like part of the problem for you is the HYPE.

That is a separate issue which I don't know how to resolve, or even to begin discussion. Should the books of Stephen H. and Brian G. be burned? Should science journalists be forced to adhere to standards? Should gee-whiz science series be banned from TV? But who would pay scientist's bills if public enthusiasm were not regularly whipped up? It is all bewildering. I don't know what to think. There is a hype problem and a general science in the media problem.

The REAL SUBSTANTIVE ISSUES of how reliable and accurate models are and what their range of applicability, where they break down, and what a more fundamental theory might look like that they might emerge from...that's different.

That needs to be discussed in an entirely different context. It consists of hundreds of different questions that fit together-----patches of clarity, patches of uncertainty. You need calm surroundings, clear of hype. You need a community of other minds trying to do the same thing.

A sample question: why do you think the redshift of the CMB is 1100?
There are a lot of reasons that fit together, you could spend part of an afternoon talking that over, reading sources, talking about it again. I remember doing that one afternoon years ago, with some grad students in the astronomy building.

Part of what you are doing is you ABSORB an intuitive feel from the others (your advisor, other students)-----what they are more skeptical about, what areas of precision they admire, what they feel dubious, where they feel more confident. There are many interlocking parts of the picture. And of course the prevailing theoretical picture is always changing! Some piece is being adjusted and refitted into the picture all the time.

And you never believe.
You try to use the best model available, and you keep testing and checking.

I think that's how it works. And there are some fields where the style or ethos probably isn't what I'm talking about, at least judging from external appearance, but that's a separate issue.

 

[OOO]

It sounds like part of the problem for you is the HYPE.

That is a separate issue which I don't know how to resolve, or even to begin discussion. Should the books of Stephen H. and Brian G. be burned? Should science journalists be forced to adhere to standards? Should gee-whiz science series be banned from TV? But who would pay scientist's bills if public enthusiasm were not regularly whipped up? It is all bewildering. I don't know what to think. There is a hype problem and a general science in the media problem.

That's an all irritating facet of science to me. On the one hand I probably wouldn't have come to physics if I had not read popular books about the Big Bang, the lifecycle of stars and black holes during my childhood. On the other hand I haven't fully realized that some things are a little more uncertain before starting my PhD last year.

It's a bit like when you first notice that Santa doesn't exist. So maybe at the moment I'm on a mission to tell the world that Santa doesn't exist, but everybody seems to know that already...

But you're right, it probably wouldn't be so good if there were no popular science books. It's not that I suppose politicians to read such books, but rather the public opinion would be less in favor of the necessity of science.

 

[Chris Hillman]

Please write more carefully

So big bang cosmology is all about thermodynamics in a gravitational background ?

No-one said that! Thermodynamical considerations play an important role, but obviously there are other elements in play. See any good cosmology textbook.

On the other hand I haven't fully realized that some things are a little more uncertain before starting my PhD last year.

In what subject? If astrophysics, what uni, may I ask?

OOO, you suggested that the Big Bang is not well a well-founded theory, arguing:

Take this from http://en.wikipedia.org/wiki/Big_Bang_nucleosynthesis as an example:
"During the 1970s, there was a major puzzle in that the density of baryons as calculated by Big Bang nucleosynthesis was much less than the observed mass of the universe based on calculations of the expansion rate. This puzzle was resolved in large part by postulating the existence of dark matter."

This is one argument used by many "creationists", but it fails to take account of something which good physics students recognize, perhaps without really thinking of it, but which laypersons almost never recognize. Namely, cosmology consists of an intricate and tightly interwoven network of observations glued together by a hierarchy of more or less well established theories. At anyone stage in the development of cosmology, there have been various mysteries such as the "missing neutrinos" or the "missing matter". The observations which gave rise to these problems didn't destroy the network but enriched it, however much they might have strained some of the existing theories used to tie the thing together. History suggests that each of these problems is eventually resolved, sometimes in ways which can be regarded as resulting in "revolutionary reinterpretations" but which in another sense change less than laypersons might expect. IOW, cosmology is above the cosmological evidence, and this is more solid and more solidly interconnected than you might yet appreciate. Similarly, the edice of mainstream physical theory is hierarchical, and the foundations are much more solid than you might yet appreciate from reading popular science descriptions of speculations about traversable wormholes, colliding branes (to mention two random examples of hypothetical creatures which are not currently supported by evidence, and which may turn out to be another pink unicorn, or just possibly, the next kha-nyou ).

 

[OOO]

I think my initial question has been answered satisfactorily. I acknowledge now that the majority of cosmologists seems to be much more careful about their models than any popular account might make us believe. Taking the Big Bang theory as the hypothesis that currently explains the history of our universe better than any alternative is a tenable scientific position.

Thank you all for this insightful discussion.

 

[russ_watters]

The evidence you speak of is an indirect one. Nobody has ever seen a galaxy fly away.

We see 10,000 of them in the HUDF.

And what's more, we can't do experiments with galaxies in their natural environment.

That's a red herring: Experiments and observations are the same thing. The universe is doing the experiments for us - we just need to watch.

So we have to rely on the assumption that physics is everywhere the same in the universe...

Yes, that is a fundamental requirement of science. What's the problem with it? (If it is wrong, it is still pointless to debate this because it means no other theory could ever be right either - scientists should just pack up their telescopes and go home.)

And even the theories we design to explain these experiments change on a timescale that's infinitesimal compared to the timescale of the universe.

I'm not sure what you mean by that - scientists constantly refine theories. That's what science is about. But you are also using the same red herrring 'it-can't-be-tested' argument as anti-evolution crackpots say. Don't be that guy.

 

[russ_watters]

I acknowledge now that the majority of cosmologists seems to be much more careful about their models than any popular account might make us believe.

I find it very odd that you'd take what you see in popular accounts to be a complete treatment of the theory. People spend their entire lives studying this stuff and they aren't complete idiots. You should assume there is more to it than you can learn in a 10 minute read of a popular science article. It is naive and/or arrogant to believe otherwise.

Taking the Big Bang theory as the hypothesis that currently explains the history of our universe better than any alternative is a tenable scientific position.

Please don't call it an hypothesis. It makes it sound like you are putting it down.

But yeah, it explains things better than any other theory.

Again - why would you assume otherwise? Why assume scientists are, as a group, blind, drunken rats running randomly through a maze?

C'mon - be reasonable and give scientists the benefit of the doubt they deserve.

 

[OOO]

That's a red herring:

First of all, insinuating that I tried to baffle someone is a little bit paranoid, isn't it. In my experience if somebody mentions "red herrings" he usually tries to throw in a red herring himself. So let's stick to the facts.

Experiments and observations are the same thing.

Of course not. One can always take all ones observations and create fanciful theories around them which nobody can falsify. That's usually the reason why people get into arguments about nothing. If the alleged equivalence between experiment and observation is your preferred interpretation of the role of physics then continuing this discussion is futile.

Yes, that is a fundamental requirement of science. What's the problem with it? (If it is wrong, it is still pointless to debate this because it means no other theory could ever be right either - scientists should just pack up their telescopes and go home.)

You're getting a little emotional now. Whether scientists should pack their telescopes and go home is beyond the scope of this discussion. But I need not remind you that if Johannes Kepler had packed his telescope and gone home he would not have noticed that the apparent movement of the sun around the Earth is the result of anthropocentric thinking.

Is it really so far fetched that the assumption of our current physics laws being everywhere the same in the universe could one day be recognized as a result of anthropocentricity again ?

But you are also using the same red herrring 'it-can't-be-tested' argument as anti-evolution crackpots say. Don't be that guy.

No, I think I'm not a crackpot. But thanks for your concern.

I find it very odd that you'd take what you see in popular accounts to be a complete treatment of the theory.

Sounds interesting, but did I really say that ? Didn't I rather express my skepticism here in this forum and ask the experts about what makes them so sure about the Big Bang theory ?

Please don't call it an hypothesis. It makes it sound like you are putting it down.

If it makes you nervous, I won't.

Again - why would you assume otherwise? Why assume scientists are, as a group, blind, drunken rats running randomly through a maze?

As you say it this way... I'm almost beginning to feel sorry for this group I thought I belonged to.

 

[pervect]

Of course not. One can always take all ones observations and create fanciful theories around them which nobody can falsify.

Is it really so far fetched that the assumption of our current physics laws being everywhere the same in the universe could one day be recognized as a result of anthropocentricity again ?

I think this is probably the wrong question. A better question is: is there any evidence that "the laws of physics" are changing? Is there any way to test this notion that "the laws of physics are changing", or is it one of those "fanciful theories that nobody can falsify"?

 

[OOO]

I think this is probably the wrong question. A better question is: is there any evidence that "the laws of physics" are changing? Is there any way to test this notion that "the laws of physics are changing", or is it one of those "fanciful theories that nobody can falsify"?

One of the criteria (besides being experimentally testable) for a theory to be better than another is whether it makes descriptions simpler. We all know the standard examples:

Example 1: The heliocentric theory was better than the geocentric because in the geocentric one the description of planetary orbits is utterly complicated
Example 2: Formulating physical laws (in the absence of gravity) in terms of Lorentz transformation is better than Galilean because the laws get simpler

Thus there would be "evidence" (in the above sense) that the "laws of physics" are changing if this leads to a simpler description of what we see (the apparent Big Bang, which immediately brings up the question, what was before it ?), than the assumption that the laws are invariable. And if this happens to be related with the question about how gravity and the standard model fit together it might also be testable with our experimental methods here on earth.

Whether a yet to propose theory is actually either falsifiable or fanciful I cannot answer, because I don't have any such theory and I am not inclined to work on cosmology.

But If nobody considers the possibility of a sort of scale-invariant (just to say something wannabe educated... ) theory, then we will never know if this provides a better description.

 

[BoomBoom]

I am curious where you are getting your ideas about who these people are and what they claim. I hope you are not talking about popular journalism or pop-sci books. I'd like to have a link to somewhere a professional cosmologist makes some unqualified claim about events and conditions.

Assertions really ought to be qualified by reservations like "according to the usual LCDM model" or "according to GR"

One of "these people" that you can't seem to get away from (at least on TV) is Dr. Neal Tyson or whatever his name is. I swear this guy is not only on EVERY space related documentary, I also see him doing the talk show circuits. It bugs me how he states as a "matter of fact" not only how our universe began, but how it will end. I'm not sure I've ever heard him utter the word "theory".

 

[BoomBoom]

That's a red herring: Experiments and observations are the same thing. The universe is doing the experiments for us - we just need to watch.

The same thing?? :O

I wonder where the world of Biology would be if we could only observe and not actually conduct experiments? We would be eons behind where we are now...

Not only are astronomical observations unrelated to any experimental perturbation with controls and such, they also are observations of the PAST. There is no possible way to observe what the distant universe is doing in real-time, which in itself can introduce a possible error in observational conclusions.

 

[Chris Hillman]

Still urging more careful expression of ideas

Example 2: Formulating physical laws (in the absence of gravity) in terms of Lorentz transformation is better than Galilean because the laws get simpler

This could easily be read as the claim that the Lorentz transformation is "simpler than" the Galilei transformation and thus "preferred by an application Occam's razor". If so, two comments:

• the Galilei transformation (for one dimensional motion) is
  t^\prime = t, \; x^\prime = x + v \, t[/itex]<br /> while the Lorentz transformations are<br /> &lt;br /&gt; t^\prime = \frac{t + v \, x}{\sqrt{1-v^2}}, \; x^\prime = \frac{x + v \, t}{\sqrt{1-v^2}},&lt;br /&gt; \; -1 &amp;lt; v &amp;lt; 1 &lt;br /&gt;<br /> Counting characters or considering radicals casts doubt on any claim that the Galilei transformation is the simpler of the two. Incidently, these are two from the triple of transformations which arise respectively from elliptic, parabolic, and hyperbolic trigonometry. The analogous &quot;slope form&quot; of the familiar transformatons of elliptic trig are of course<br /> &lt;br /&gt; y^\prime = \frac{y + v \, x}{\sqrt{1+v^2}}, \; x^\prime = \frac{x - v \, y}{\sqrt{1+v^2}} &lt;br /&gt;<br /> [*]The Galilei transformation has been ruled out because it disagrees with experiment, not by any appeal to &quot;Occams&#039; razor&quot;.<br />

<br /> <br /> [EDIT: as I suspected might prove to be the case, I seem to have misunderstood what OOO meant by the quoted statements; see below]<br /> <br /> <blockquote data-attributes="" data-quote="OOO" data-source="post: 1490474" class="bbCodeBlock bbCodeBlock--expandable bbCodeBlock--quote js-expandWatch"> <div class="bbCodeBlock-title"> OOO said: </div> <div class="bbCodeBlock-content"> <div class="bbCodeBlock-expandContent js-expandContent "> Thus there would be &quot;evidence&quot; (in the above sense) that the &quot;laws of physics&quot; are changing if this leads to a simpler description of what we see (the apparent Big Bang, which immediately brings up the question, what was before it ?), than the assumption that the laws are invariable. </div> </div> </blockquote>Presumably you intend to suggest, not simply that some &quot;law of physics&quot; is changing over time, but that the alleged change is occurring in a lawful manner. In fact, most likely you have in mind some law in which a parameter appears which you imagine to be changing over time, in fact, to be some simple function of time, perhaps even an affine function of time.<br /> <br /> <blockquote data-attributes="" data-quote="BoomBoom" data-source="post: 1490534" class="bbCodeBlock bbCodeBlock--expandable bbCodeBlock--quote js-expandWatch"> <div class="bbCodeBlock-title"> BoomBoom said: </div> <div class="bbCodeBlock-content"> <div class="bbCodeBlock-expandContent js-expandContent "> The same thing??...<br /> Not only are astronomical observations unrelated to any experimental perturbation with controls and such, they also are observations of the PAST. There is no possible way to observe what the distant universe is doing in real-time, which in itself can introduce a possible error in observational conclusions. </div> </div> </blockquote><br /> I agree that there is an important distinction between observation and experiment; only the latter is under our control, can be readily repeated under slightly different conditions, and so on. I am pretty confident that Russ appreciates this and was simply writing a bit hastily. <br /> <br /> I think we all agree that cosmology is complicated, and that weaving observations into a coherent picture glued together by myriads of insights from various theories in the hierarchy of theoretical physics is a difficult and very tricky business. However, IMO it would be misleading to claim that modern cosmology is merely fanciful house of cards. The truth is that the structure is far more robust than amateur critics tend to appreciate. Like engineering structures, the existence of a certain flexibility and &quot;room for play&quot; in the edifice of science is an essential part of its robustness.<br /> <br /> <blockquote data-attributes="" data-quote="BoomBoom" data-source="post: 1490524" class="bbCodeBlock bbCodeBlock--expandable bbCodeBlock--quote js-expandWatch"> <div class="bbCodeBlock-title"> BoomBoom said: </div> <div class="bbCodeBlock-content"> <div class="bbCodeBlock-expandContent js-expandContent "> One of &quot;these people&quot; that you can&#039;t seem to get away from (at least on TV) is Dr. Neal Tyson or whatever his name is... It bugs me how he states as a &quot;matter of fact&quot; not only how our universe began, but how it will end. I&#039;m not sure I&#039;ve ever heard him utter the word &quot;theory&quot;. </div> </div> </blockquote><br /> Neal Degrasse Tyson runs the Hayden Planetarium in NYC and performs other duties, including http://research.amnh.org/~tyson/ at the American Museum of Natural History. (Not every visitor realizes the top floors of this vast building are a fully functioning and active and prestigious research institution.) He has a <a href="http://en.wikipedia.org/wiki/Neil_deGrasse_Tyson" target="_blank" class="link link--external" rel="nofollow ugc noopener">wikibio</a> which at a glance looks pretty decent at the time of my visit, but the usual caveats apply.<br /> <br /> I happen to really like the PBS shows Tyson is making, but it might help to think of PF as a place you can go for more depth.

 

[OOO]

Counting characters casts doubt on any claim that the Galilei transformation is the simpler of the two.

I have implicitely assumed that this forum isn't kindergarten level. Lorentz invariance originally stems from Maxwell's equation. You can also Galilei transform Maxwell's equations, but then you get a different set of equations for every frame. Is that complicated enough to state that Lorentz transforms are simpler ?

[*]The Galilei transformation has been ruled out because it disagrees with experiment, not by any appeal to "Occams' razor".
[/list]

You can even Galilei transform the Lorentz force, or quantum field theory, or whatever you want. The fact that you normally don't do this is because you have finite mental energy and you'd like to achieve infinitely many results and so this is in fact a representation of an economic principle.

What you seem to be referring to is the actual form of the law that doesn't follow from Occam, but well, I know that of course.

Presumably you intend to suggest, not simply that some "law of physics" is changing over time, but that the alleged change is occurring in a lawful manner. In fact, most likely you have in mind some law in which a parameter appears which you imagine to be changing over time, in fact, to be some simple function of time, perhaps even an affine function of time.

I think what I had in mind is irrelevant because it would be mere conjecture. Moreover it should only serve as an example for the fact that there could always be alternative explanations, some of which might probably less straining to the mind than a universe that began as a hard cut 13 billion years ago. Whether we expect it to be found in a cosmological term, or conformal field theory or whatever, doesn't matter.

 

[pervect]

One of the criteria (besides being experimentally testable) for a theory to be better than another is whether it makes descriptions simpler. We all know the standard examples:

Example 1: The heliocentric theory was better than the geocentric because in the geocentric one the description of planetary orbits is utterly complicated
Example 2: Formulating physical laws (in the absence of gravity) in terms of Lorentz transformation is better than Galilean because the laws get simpler

Thus there would be "evidence" (in the above sense) that the "laws of physics" are changing if this leads to a simpler description of what we see (the apparent Big Bang, which immediately brings up the question, what was before it ?), than the assumption that the laws are invariable. And if this happens to be related with the question about how gravity and the standard model fit together it might also be testable with our experimental methods here on earth.

Whether a yet to propose theory is actually either falsifiable or fanciful I cannot answer, because I don't have any such theory and I am not inclined to work on cosmology.

But If nobody considers the possibility of a sort of scale-invariant (just to say something wannabe educated... ) theory, then we will never know if this provides a better description.

You might want to look up J Magueijo. While I"m personally not particularly impressed by his theories, he has come up with a theory that actually makes testable predictions along those lines, if you consider "varying speed of light" to be "varying physics".

I think of it as a bit of a "dancing bear" theory, where the point is not that the theory is very elegant,the amazing thing is that it dances at all. YMMV, but it's published (in peer reviewed journals) and it makes actual predictions. However, AFAIK there isn't a shred of evidence that suggests this theory is actually true. It's mostly useful IMO as a testbed to compare with more viable theories.

http://arxiv.org/PS_cache/astro-ph/pdf/0703/0703751v1.pdf by Ellis has some references to Jagueijo and some comments on VSL.

There's also a rather controversial paper by Duffy about VSL that's worth reading even if it may not be totally correct, unfortunately I don't remember where it was and couldn't find it with a quick search.

If you don't consider VSL to be "varrying physics", I've guess I've just wasted a few minutes of both of our time, I suppose :-).

 

[Chris Hillman]

Musings on the "Appropriate Level" for PF posting

I have implicitely assumed that this forum isn't kindergarten level. Lorentz invariance originally stems from Maxwell's equation. You can also Galilei transform Maxwell's equations, but then you get a different set of equations for every frame. Is that complicated enough to state that Lorentz transforms are simpler ?

OK, OOO, to be fair to you, I agree that I appear to have misunderstood what you had in mind in the comment I objected to, but to be fair to myself, you should acknowledge that your intent was not clearly expressed.

As you probably realize, PF is a public forum which attracts posters with a huge variety of backgrounds, from junior high schoolers to a handful of professional researchers with more or less expert knowledge of the subjects they post about here. It can be almost impossible to judge someone's background on the basis of having seen just a few posts, and inevitably jaded participants like myself do tend to reduce to a lowest common denominator in the absence of evidence to the contrary. Don't take it personally if I have misjudged your background and knowledge; once you have established a longer posting history and "regulars" have had a chance to see you exhibit some good knowledge or insight, we will probably come to recognize your "handle". You'll be glad to know that some of us prefer to talk to posters with a graduate knowledge or beyond!

(Hmm... if you ever said whether you are a Ph.D. student in astrophysics or some other subject, I missed that. FWIW I am trained as a mathematician and am entirely self-taught in physics, but seem to have somehow acquired a reasonable working knowledge of gtr, something I have to repeat from time to time because posters often assume I must be a physicist! Welcome to the InterNet, land of self-appointed experts )

I think what I had in mind is irrelevant because it would be mere conjecture.

Are you saying that you have a particular conjecture in mind, which you don't yet wish to share? Fair enough, but to be fair to myself, you should recognize that tossing out hints could lead to further misunderstandings.

 

[OOO]

OK, OOO, to be fair to you, I agree that I appear to have misunderstood what you had in mind in the comment I objected to, but to be fair to myself, you should acknowledge that your intent was not clearly expressed.

Sorry for having appeared a little harsh. I thought I had expressed my thoughts in as natural and generally intelligible language as possible. I certainly didn't want to come to technical details because me being not a cosmologist I couldn't defend any position.

To repeat, I'm finding it odd that the universe should have begun at a singular instant in time with a huge amount of energy coming from nothing. I feel this should bring up a lot of questions even if it's possible to reconcile the Big Bang with the standard model up to the first microseconds or nanoseconds or whatever the state-of-the-art may be. In this respect I asked the expert cosmologists what makes them sure about it, and I got the answer that they are not absolutely sure but rather comparatively sure, which is OK for me.

Hmm... if you ever said whether you are a Ph.D. student in astrophysics or some other subject, I missed that.

Yes, I prefer to remain anonymous. That allows me to utter stupid things from time to time, without damaging my reputation, a prerequisite for discussing freely. Especially as I'm coming from theoretical particle physics, where you should continue to feel like a complete moron even after 20 years of experience.

Are you saying that you have a particular conjecture in mind, which you don't yet wish to share? Fair enough, but to be fair to myself, you should recognize that tossing out hints could lead to further misunderstandings.

My own (diffusely expressed) conjecture that the universe could probably be somehow eternal so that what we extrapolate as 13 billion years is actually negative temporal infinity, was just a dumb example of an explanation that calls for less trouble, in my opinion.

I have no theory fragment that expresses this view, so I have nothing to share in this respect. However it seems natural to me, that combining a theory like general relativity (in which you could well choose a coordinate system where t=-13000000000yr is mapped to t=-infinity) with the standard model (where there are natural timescales because there are fixed masses and couplings) could easily lead to such conclusions as the apparent Big Bang. My feeling is that this will be happily resolved as soon as there is a unified theory, because then it will probably be possible to simply choose a coordinate system where no singularity occurs.

But I can already hear people barking at me for saying the above, so I better shut up now.

 

[EL]

OOO, if I interpret you right, you are saying something like you find it strange to say that the universe is 13,7 billion years old when we don't know what laws of physics to use above 100 GeV?
In that case I am willing to agree with you.
I think we have a good model of what happened from the 100 GeV scale until now, and we know with rather high precision that this journey took 13,7 billion years. Before that, it of course gets more speculative, but we have (a more or less) promising (but speculative) rough model which takes us all the way back to the proposed period of inflation. A short time before this inflation started the energy scales are huge and we (who are not doing stuff like string theory) have basically no idea what happened. Maybe you can squeeze in your infinite period of time here?

 

[OOO]

Maybe you can squeeze in your infinite period of time here?

Instead of squeezing something into that period we probably ought to squeeze something out of our brains.

I think it can't be just a question of temperature but rather a question of boundary conditions. Thermodynamics is used for cooking pea soup.

If you have a balloon which you let burst and afterwards you ask your naive friend to measure the velocity field of the expanding gas then he will come to the conclusion that the gas originated from a single point. He will tell you that there must have been a "Big Bang" some time ago and he proudly presents his calculation of the first millisecond where the temperature was 1000 degrees centigrade and there was nitrogen oxide and ozone and all that. (just for the minutes: naaah, I don't believe the universe was once packed into a giant balloon, that was just a parable )

To unveil the truth, your friend will have to learn about balloons. Before he hasn't got a "balloon theory" he may engage in various speculations. Likewise we can tell each other our wild guesses here. But in the end the (experimentally verified) theoretical tools of our time will decide what we are able to understand and what we don't.

PS: I know that the gas molecules from the balloon wouldn't match in a single point, but without that it wouldn't be such nice story...
PPS: But now I'll button my lips. Really.

 

[EL]

If you have a balloon which you let burst and afterwards you ask your naive friend to measure the velocity field of the expanding gas then he will come to the conclusion that the gas originated from a single point. He will tell you that there must have been a "Big Bang" some time ago and he proudly presents his calculation of the first millisecond where the temperature was 1000 degrees centigrade and there was nitrogen oxide and ozone and all that. (just for the minutes: naaah, I don't believe the universe was once packed into a giant balloon, that was just a parable )

Ok, I think I'm getting closer to get what you mean.
You are saying something like the universe at some point, say X billion years ago, was in a state (however it got there) which, using the physical laws as we know them, looked exactly like it was originating from a big bang, right? (This corresponds to your balloon before it bursts.)
First of all, this could actually be more of a philosophical question. How do you know the universe didn't come into existence just a second ago, with all memories planted in your brain, and everything looking just like it was created 13,7 billion years ago just because it was finely tune to look like that? These kind of claims are of course not scientifically testable.
On the other hand, in order for "your" model to be scientific, it need to produce new predictions that can be observed and be used to discriminate it from the Big Bang model.
Remember also that the Big Bang theory predicts a number of observations which are set up from physical processes before "your balloon bursted". In the Big Bang model the CMB originates from (13700000000 - 300000) years ago, while the hydrogen/helium abundances were synthesised (13700000000 - 0.000003) years ago. The alternative model of course also needs to reproduce the prediction of a CMB and the same relative abundances of light elements.

 

[Garth]

ABB (Before Balloon Burst) and ABB (After Balloon Burst)..

Could not these eras of 000 correspond to the pre and post Inflation era? After all a balloon burst would represent Inflation pretty well! (In the crudest sense of course)

One question to ask is: "What is preserved as standards of mass length and time through the Inflation era?"

If the Higgs field suddenly 'bombs' and deposits a load of mass-energy into the universe what happens to the standard mass kilogramme?

Of course there were no atoms around at that time, so atomic methods and standards of measurement pre, during and post Inflation are anachronistic, and that fact raises a question in itself. (What is a second in that era when there were no clocks to measure it?)

However, if particle inertial masses suddenly increased then that would speed up the rate of atomic clocks, so reversing the process might well map the instant of the BB back to t = - \infty!

Just a thought.

Garth

 

[OOO]

However, if particle inertial masses suddenly increased then that would speed up the rate of atomic clocks, so reversing the process might well map the instant of the BB back to t = - \infty!

As far as I can tell from your words, this is exactly the kind of phenomena I was thinking of. (Oops, I've broken my vow of silence again this is quickly getting out of control)

 

[Chris Hillman]

A Good Book

OOO, if I interpret you right, you are saying something like you find it strange to say that the universe is 13,7 billion years old when we don't know what laws of physics to use above 100 GeV?
In that case I am willing to agree with you.

I think it is crucially important to stress that what cosmologists really believe is not quite "the universe began 13.7 billion years ago" but rather "we can begin to describe the evolution of the universe beginning 13.7 billion years ago, when it was much hotter and denser and...".

To repeat, I'm finding it odd that the universe should have begun at a singular instant in time with a huge amount of energy coming from nothing.
...
My own (diffusely expressed) conjecture that the universe could probably be somehow eternal so that what we extrapolate as 13 billion years is actually negative temporal infinity, was just a dumb example of an explanation that calls for less trouble, in my opinion.

I have no theory fragment that expresses this view, so I have nothing to share in this respect. However it seems natural to me, that combining a theory like general relativity (in which you could well choose a coordinate system where t=-13000000000yr is mapped to t=-infinity) with the standard model (where there are natural timescales because there are fixed masses and couplings) could easily lead to such conclusions as the apparent Big Bang.

Hawking and Ellis, The Large Scale Structure of Spacetime, Cambridge University Press, 1973.

IMO as a past or future physicist with an interest in cosmology, you really ought to read it. This would clear up some rather serious misconceptions which IMO are evident several of your comments above.

OK, I'll bow out here since I find I am repeating myself

OOO, I have put you in my ignore list and suggest that you put me in

Yours

 

[OOO]

Hawking and Ellis, The Large Scale Structure of Spacetime, Cambridge University Press, 1973.

IMO as a past or future physicist with an interest in cosmology, you really ought to read it. This would clear up some rather serious misconceptions.

OK, I'll bow out here since I find I am repeating myself

Perhaps we have just no common mode of communication. You think you have to teach me the basics of differential geometry and I am asking myself what you are insisting on that isn't apparent from your speech.

 

[OOO]

Ok, I think I'm getting closer to get what you mean.
You are saying something like the universe at some point, say X billion years ago, was in a state (however it got there) which, using the physical laws as we know them, looked exactly like it was originating from a big bang, right? (This corresponds to your balloon before it bursts.)
First of all, this could actually be more of a philosophical question. How do you know the universe didn't come into existence just a second ago, with all memories planted in your brain, and everything looking just like it was created 13,7 billion years ago just because it was finely tune to look like that? These kind of claims are of course not scientifically testable.

This is what I wanted to say all the time since my first post. Take a bucket of white wall paint, put in some red paint, stir heavily, and what you finally get is a bucket full of light pink wall paint. No information about how it began. You could well have gone into the store and have bought that bucket of light pink paint from the shelf.

But if you have a theory that describes very accurately what you observe (in our case: you see the dirty wall and remember that you wanted to give it a new paint), you might be able to conclude that most probably you mixed the paint yourself, although you can't deduce this from the present state of the paint alone.

Remember also that the Big Bang theory predicts a number of observations which are set up from physical processes before "your balloon bursted". In the Big Bang model the CMB originates from (13700000000 - 300000) years ago, while the hydrogen/helium abundances were synthesised (13700000000 - 0.000003) years ago. The alternative model of course also needs to reproduce the prediction of a CMB and the same relative abundances of light elements.

I can't see why this should rule out every other possibility. Once again think of particle masses being variable under extreme conditions. Who can say that the above figures wouldn't get a different meaning when judged with a different theory. Of course, pervect is right as he remarked about the question, whether there is evidence for that at all.

Thus I remind you once again, that I have no theory. I just say that terrestrial physics could lead to new theories that, if interpreted consequently, unequivocally lead to a different interpretation of what we now conceive as the Big Bang. I guess this is a rather weak statement, so I don't understand why saying this upsets some people that much.

I just hate NoGo theorems and NoGo-like thinking. NoGo's are rather stupid robots. Send them to tidy the room and they kill your mother.

 

[EL]

I think it is crucially important to stress that what cosmologists really believe is not quite "the universe began 13.7 billion years ago" but rather "we can begin to describe the evolution of the universe beginning 13.7 billion years ago, when it was much hotter and denser and...".

Exactly, that is my point.
I advocate to define t=0 (i.e. "when the big bang took place") right at the end of inflation. After all, the reheating at the end of the inflationary period "created" all the particles, just like the common notion of "the big bang creating everything". In this way we can say "inflation ended 13,7 billion years ago" instead of refereing to the age of the universe. Alternatively we can define our universe just as the one which came into existence after inflation.

 

[EL]

I can't see why this should rule out every other possibility.

Well, it doesn't.

Who can say that the above figures wouldn't get a different meaning when judged with a different theory.

Sure, but the different theory still needs to reproduce what we observe today (the CMB and the hydrogen/helium abundancies). Of course the origin of the CMB and light element abundancies need not be the same.

Thus I remind you once again, that I have no theory.

I know, that's why I wrote "your" theory within quotation marks.

I just say that terrestrial physics could lead to new theories that, if interpreted consequently, unequivocally lead to a different interpretation of what we now conceive as the Big Bang.

Well, sure it "could" happen, who knows? On the other hand I think we have a rather good understanding of the physical laws up to say 100 GeV. But it seems you do not agree with this, or?

 

[OOO]

On the other hand I think we have a rather good understanding of the physical laws up to say 100 GeV. But it seems you do not agree with this, or?

If you refer to the Big Bang: since you already know that I'm no cosmologist, you can't expect that I agree with something, I have almost no knowledge about. But it's safe to say, that I trust these many people who have combined the presently known physics in a reasonable way to get a reasonable theory of the Big Bang.

If you refer to the Standard Model: yes, it's experimentally quite well-tested. But the essential information has to be put in by hand, which seems to be unsatisfactory in the light of the alleged "rather good understanding". Moreover the attempt to get predictions in the non-perturbative regime leads to very hard calculations, either analytically or on the lattice. Thus the formation of bound states of quarks isn't nearly as well-understood as many people would hope.

 

[EL]

If you refer to the Standard Model: yes, it's experimentally quite well-tested. But the essential information has to be put in by hand, which seems to be unsatisfactory. Moreover the attempt to get predictions in the non-perturbative regime leads to very hard calculations, either analytically or on the lattice. The explanation of bound states of quarks isn't as well-understood as many people would hope.

I am mainly referring to GR, thermodynamics, statistical physics, atomic physics, nuclear physics and the Standard Model!
We don't have to "explain" all experimental results in order to use them empirically.

 

[OOO]

I am mainly referring to GR, thermodynamics, statistical physics, atomic physics, nuclear physics and the Standard Model!
We don't have to "explain" all experimental results in order to use them empirically.

In this respect I admit that I am a bit theoretically biased.