The Big Bang time paradox

[Dauphin]

KH's DL.

[KrazyHorse]

Originally posted by aneeshm
But the paradox remains - which means that time cannot have a beginning.

This is predicated on a number of untested hypotheses, not the least of which is the assumption that the passage of the coordinate we label "time" is necessary to effect changes in the physical state of a system in an energy domain we have never observed.

[LDiCesare]

Anybody with half a brain can come up with a dozen different models for the creation of the Universe which are self-consistent and also consistent with all known data. That's not science; it's science fiction.

Wouldn't it be science if said half-brained person also proposed a new test that could invalidate that theory?

I find it funny to see people are troubled with the idea of a finite time when most people are unable to grasp the idea of an infinite universe (length).

[LordShiva]

Originally posted by Dauphin
KH's DL.

Ha! I knew he was a DL (but I thought he was Locutus').

[KrazyHorse]

Originally posted by Diadem


Such arrogance.

You know it, baby.

Not everybody has the time to study physics in dept. I can not blame them, it takes several years to understand stuff like this.

As far as I'm aware, this does not make them lesser human beings. Also, it does not forbid them from speculating about such fundamental questions as 'where do we come from'.

It sure as hell makes their opinions or objections on those subjects fundamentally irrelevant to me.

So not only are you arrogant, you are also ignorant. Impaler's answer was spot on. In fact it's not often you see such a clear explanation of the philosophical problem.

No, his answer was an attempt to solve a problem which does not exist. The objection was to a postulated "beginning of time" in supposed "Big Bang theory". Neither of those ideas are necessary, or indeed, desirable at this moment in time.

And his "solution" of the philosophical "problem" was a simple cop-out. A chain of causality still links the Universe at any moment with all of its anteceding physical states. Thus there remains the theoretical possibility that we may at some point extract data about those states, and might well be required to explain them. Whether or not "time" and "space" will remain useful concepts in such an investigation remains to be seen.

The concept of 'time before time' is meaningless. Just like the concept of 'space outside space' is meaningless. Something that does not exist does not have properties. Space and Time were created along with the universe. While this does not explain why the universe is there, it does explain the question aneeshm asked, about time before the Big Bang.

If you are truly a physicist, then you should be more aware of the limits of your own knowledge. The preceding paragraph demonstrates an unsound willingness to speculate based on zero information. It also manages to ignore what I've now repeated three times: that the "Big Bang" is not an element in standard modern cosmology. An instant of creation has been replaced by a view of the Universe proceeding from a pre-inflation state to a post-inflation state. The pre-inflation Universe has a non-infinitesimal extent in both time and space. In fact, there are real physical constraints which can be put on those dimensions (both upper and lower). There is no particular reason to believe much else about this pre-inflation Universe, and there is especially no reason to believe that it proceeded at any point from a physical state in which time "did not exist".

[Zkribbler]

Originally posted by KrazyHorse

I've never seen a proposed mechanism for the explosing, but my own pet concept is the collisions between matter and anti-matter, which will occur more often as the universe contracts.

That is ruled out. No known physical mechanism can explain inflation.

Inflation in a static-sized proto-universe as postulated by the Big Bang theory or inflation in a contracting universe as postulated by the Big Bounce hypothesis?

[KrazyHorse]

Originally posted by Diadem
Ah, so it's turtles all the way down, after all?

Are you stupid, or just careless?

The "turtles all the way down" analogy would come into play were I to postulate a Universe that has been in existence for an infinite amount of time. I make no such claim. I have a good idea what the overall evolution of the Universe has looked like for the last 13.6 billion years. I have a bad idea what it looked like for a much shorter period of time before that (whose duration is also very uncertain). I have no idea what it looked like for any point prior to that.

Cosmology cannot, indeed. But philosophy can. And behold! The topic starter's question was a philosophical one.

No, it wasn't. It attempted to be a "philosophical" question about a scientific theory. What it ended up being was a demonstration of the author's ignorance of the scientific theory. The answer to his "question" is thus purely scientific; to correct his misrepresentation of the theory and to explain why the supposed dilemma is not relevant to the actual theory.

Anyway for someone who claims to be a professional cosmologist you are surprisingly badly informed about matters. Claiming there is no big bang, just inflation? Since when is inflation theory a replacement of the big bang theory? It's a refinement, nothing more. The basic theory of the 'big bang' still stands as soundly as ever.

This is completely wrong. What the hell branch of physics do you study? What university are you at?

Our physics can not describe the Big Bang itself. But we can infere that a Big Bang must have taken place.

No, we can't.

That is, we can convidently state that everything we can observe must once have been compressed together into a infinitessimally small point.

Untrue. If you understood the first thing about inflation you would understand why this claim is spurious. The simple existence of an inflatonic field whose behaviour is badly understood should explain to you why it is impossible to trace the expansion of the Universe backward any further than the inflationary epoch. Our physics doesn't work backwards past inflation. The singularity-generated Big Bang is only mandated if you presume that the expansion of the Universe happened fundamentally according to processes we understand. This presumption is thus not only unjustified, but demonstrably false.

[KrazyHorse]

Originally posted by Zkribbler


Inflation in a static-sized proto-universe as postulated by the Big Bang theory or inflation in a contracting universe as postulated by the Big Bounce hypothesis?

Either. Radiation pressure generated by mater annihilation cannot drive the requisite exponential expansion.

[Diadem]

Originally posted by KrazyHorse


It sure as hell makes their opinions or objections on those subjects fundamentally irrelevant to me.

Be a bit more proud about your profession man! What kind of physicist are you if you aren't even willing to explain a few simple questions to laymen.

And yes, answering questions involves listening to what those questions are. Shocking, isn't it?

No, his answer was an attempt to solve a problem which does not exist. The objection was to a postulated "beginning of time" in supposed "Big Bang theory". Neither of those ideas are necessary, or indeed, desirable at this moment in time.

So it's not a necessary feature of the Big Bang. So what? It's still an interesting philosopical question. Did time have a beginning or was it always there. If it began, what was there before it began. Those are questions so fundamental they are applicable to any theory - Big Bang, Inflation, Young-Earth Creationism, etc, etc.

And his "solution" of the philosophical "problem" was a simple cop-out. A chain of causality still links the Universe at any moment with all of its anteceding physical states. Thus there remains the theoretical possibility that we may at some point extract data about those states, and might well be required to explain them. Whether or not "time" and "space" will remain useful concepts in such an investigation remains to be seen.

No it's not a cop-out. We have time now. At least we appear to have time now. Speculations about its nature and origin are valid questions. Even if they are staged in hypothetical universes.

If you are truly a physicist, then you should be more aware of the limits of your own knowledge. The preceding paragraph demonstrates an unsound willingness to speculate based on zero information.

There is nothing wrong with a willingness to speculate. As long as you realise that you are speculating. Sometime speculations give very insightful results. Did not almost all theories start as a speculation, even before they became a hypothesis?

It also manages to ignore what I've now repeated three times: that the "Big Bang" is not an element in standard modern cosmology. An instant of creation has been replaced by a view of the Universe proceeding from a pre-inflation state to a post-inflation state. The pre-inflation Universe has a non-infinitesimal extent in both time and space. In fact, there are real physical constraints which can be put on those dimensions (both upper and lower). There is no particular reason to believe much else about this pre-inflation Universe, and there is especially no reason to believe that it proceeded at any point from a physical state in which time "did not exist".

Noone ever said that the Big Bang was the moment of creation. All I said is that everything that we can see today - our whole observable universe (a sphere with a diameter of about 30 billion light years) must have once been compressed in a very tiny space. I used the word infinitessimal, and I guess I should not have. I used the word in the informal meaning of 'something very small', not the mathematical one.

Anyway, this point, moment, whatever, we call the Big Bang. We know it must have been there.

What there was before the Big Bang we don't know. Perhaps another universe and a Big Crunch, perhaps nothing, and the Big Bang was the moment of creation. For all I know the Big Bang may have been happening for all eternity - an infinitely large infinitely dense point expanding and growing less and less dense for an infinite time until it reached finite density at the moment we call Big Bang. It's as good an explanation as any.

You are right that this is not physics. It's pure speculation. But that does not mean we can not say anything about it. We can speculate, and look at how logically consistent our speculations are. This is not the domain of science-fiction, as you to think, but of philosophy.

And no matter what you say: Most physicist seem to privately hold the view that the Big Bang was the creation of the universe, and Time and Space did not exist before it. Not a physical theory, but a view (or believe) held by most physicists none the less.

Which makes questions about this 'theory' particularly interesting.

[KrazyHorse]

It's very simple: at a point some thirteen and a half billion years ago the Universe emerged from an exponential expansion driven by an unknown physical process. Our knowledge of the history of the expansion of the Universe is cut off by the existence of this process. At the point where somewhat-confident projections give way to pure speculation the Universe already had finite extent. Projecting any further back toward a singularity is ridiculous until we understand the process which drove inflation.

There are still a number of cosmologists who get very sloppy about their terminology and talk about a Big Bang occurring at a definite point in the past, but if you actually ask them if a singularity is necessary then any good one will tell you that we simply don't know. We do know that the Universe was probably significantly smaller at some point prior to inflation than at the moment inflation started, but there is no necessity for it ever to have been infinitesimally small.

[KrazyHorse]

Originally posted by Diadem

Noone ever said that the Big Bang was the moment of creation. All I said is that everything that we can see today - our whole observable universe (a sphere with a diameter of about 30 billion light years) must have once been compressed in a very tiny space. I used the word infinitessimal, and I guess I should not have. I used the word in the informal meaning of 'something very small', not the mathematical one.

Anyway, this point, moment, whatever, we call the Big Bang. We know it must have been there.

THIS IS THE WHOLE POINT.

Small does not equal infinitesimal.

There is no necessity to get rid of time or space. There is no requisite singularity. Thus the whole idea that "time started with the Big Bang" is ridiculous. And it's not helpful when people who should know better throw around words like "infinitesimal" when they mean "really small".

[Zkribbler]

Originally posted by KrazyHorse
Either. Radiation pressure generated by mater annihilation cannot drive the requisite exponential expansion.

"Exponential expansion??" When I wasn't looking, did someone get rid of Hubble's Constant??

(Dammit, ignore cosmology for a few short years, and the whole science goes on some LSD-acid trip )

[KrazyHorse]

did someone get rid of Hubble's Constant??

Hubble's constant was never a constant. Even without inflation you require that the expansion rate of the Universe changes with time. Hell, even without dark energy or dark matter you require that.

One of the reasons we know about dark energy is that the experiments designed to measure the expected cosmic deceleration (i.e. a decreasing Hubble constant) ended up coming back with cosmic acceleration (i.e. an increasing Hubble constant).

[Odin]

KH, what's you opinion on the "Ekpyrotic" cyclical model of Paul Steinhardt?

http://en.wikipedia.org/wiki/Ekpyrotic

http://en.wikipedia.org/wiki/Cyclic_model

[KrazyHorse]

Not much.

It seems wacky and unnecessarily complex.

I am not at all an expert in brane physics, however.