Big Bang Theory versus Speed of Light theory

[LegalEagle]

Hi all.

Sadly I am one of those long time lurkers that never posts - a fear of ridiculing myself on the forums I suggest.

Anyway I am wondering (and this has probably been raised before) if the Big Bang theory and the Theory or Principal of the Speed of Light being the fastest known speed are compatible.

By that, it is suggested that the fastest known speed obtainable is the speed of light. Yet, if one examines the Big Bang theory, in the first few moments of the creation or existance of the universe, the "explosion" was such that matter expanded so rapidly that it exceeded the speed of light (at least that is my understanding - the words "that it exceeded the speed of light" are my own).

I have not had time to research what the scientists believe was the speed of the universe expanding in the initial phases, however am perhaps throwing this out more as a general question (if in fact there is any inconsistency). It may well be that the Big Bang theory does not contradict the speed of light being the fastest known speed, in that the universe expanded close to the speed of light.

[tnjrp]

AFAIK they are very commonly seen to be quite comfortably compatible. Here for example is a classic-style answer to your question attributed to Rutgers University Professor of Physics emeritus Dick Plano:

Nothing can travel faster than
the speed of light through space. This does not, however, limit the speed
at which space can expand. In the first 1E-35 seconds (that is 0.00..(34
zeroes)..01 seconds after the big bang the universe expanded to a diameter
of something like 1 meter carrying all matter with it. So it was expanding
something like 3E26 (that is 3 followed by 26 zeroes) times faster than the
speed of light! And that includes the matter that was just sitting there at
rest in space. Although it is not moving relative to space (whatever that
means), a piece of matter can be increasing its distance from another piece
of matter at speeds much faster than the speed of light if the space is
expanding rapidly enough

This is a bit of simplification of course but that's basically how it's thought to go down.

[antoniseb]

As per member suggestion, I have moved this to Q&A from ATM.

[astromark]

A quick search of the astronomy news page will soon give up the article on this very question... 'That there is no velocity faster than c.' But the universe while expanding could seemingly have busted its own rule. But, no it was space time expansion not movement of matter... yes that makes the Dark Energy all powerful... Gravity being the weaker force. Waiting for more information to better comprehend this issue. As with many questions regarding the expansion of the early universe. We do not have all the information required yet to answer this question definitively. mark.

[LegalEagle]

Thanks for the replies.

My background is in law i.e. I am a solicitor. I should have done more research before posting.

My thoughts were mainly on the potential of "faster than light" travel and its possibility - hence why I posted in the Non-Mainstream area. However I did not expand on my original post, so cannot expect forum members to mind-read where I was coming from!

[slang]

Try searching the Q&A subforum for the term FTL, and you should find a few threads that explain quite in depth the impossibility of faster than light travel (if general relativity holds).

[Kwalish Kid]

yes that makes the Dark Energy all powerful... Gravity being the weaker force.

Dark energy, in all its forms, works through gravity, it is not an opposing force.

[TonyE]

I think you are refering to the period of "inflation" that, according to one current cosmological theory, happened very soon after the big bang. Inflation is a short period of exponential expansion that has been proposed to explain why the universe appears flat, homogeneous and isotropic.

During inflation the entire universe expanded "faster than light" however it is not proposed that anything inside the universe was travelling locally faster than light.

In any case, the whole inflation theory cannot be explained in terms of current mainstream physics.

[Kwalish Kid]

I think you are refering to the period of "inflation" that, according to one current cosmological theory, happened very soon after the big bang. Inflation is a short period of exponential expansion that has been proposed to explain why the universe appears flat, homogeneous and isotropic.

During inflation the entire universe expanded "faster than light" however it is not proposed that anything inside the universe was travelling locally faster than light.

In any case, the whole inflation theory cannot be explained in terms of current mainstream physics.

Inflation is one example of FTL separation, but it is not the only one. In plain, vanilla general relativistic cosmology, it is the case that the expansion in the very early universe was much faster than the speed of light. Inflation is usually posited to come after that expansion had significantly slowed. Additionally, in vanilla relativistic cosmology, galaxies far apart from each other can be expanding away from each other at greater than the speed of light billions of years into the history of the universe, because expansion "velocity" increases with distance.

[Ken G]

That is all true, and what's more, it is quite easy to get the distance between objects to grow faster than the speed of light-- for example, the distance between two oppositely directed photons increases at the rate 2c, even in special relativity, from your point of view between the photons. Of course, we are not in the frame of either photon, so you could still claim that no object can separate from us at faster than c, but even that is only true in special relativity. It is an artifact of the way special relativity pretends there is such a thing as a "global reference frame", such that the observer could be at many different locations at once and still describe the processes that are happening in the same way. In general relativity (and in reality), the observer is only at one place, and cannot speak about distant events as though they were there in any but a completely conceptualized way. When conceptualizing distant events, it is quite allowable to conceptulalize their distance from you as growing faster than c, what is impossible is to observe an object moving past you, at the place where you are (and so can make actual observations), faster than c.

Note that the way people normally talk about FTL travel requires motion past you at the place where you are, faster than c. So that's what is ruled out by relativity, even though cosmology allows it for distant objects whose motion we can only conceptualize.

[brother_unknown]

To the contrary, the scalar field has been expanding at a constant speed forever. This speed has determined the speed of light.

[Ken G]

Please define what you mean by the "expansion" of a "scalar field", in the context of their relation to the speed of something. In science, it is rather important for the words to mean something specific, or else people might think it was just gibberish.

[Swift]

To the contrary, the scalar field has been expanding at a constant speed forever. This speed has determined the speed of light.

brother_unknown,
This area is for mainstream answers to physics and astronomy questions. If you are advocating an non-mainstream idea (what we usually called Against the Mainstream or ATM), please do that in the ATM forum. Thanks for your cooperation.

[rommel543]

I know this is bordering on ATM, but would the expansion also correlate to the theory of wormholes, folding space, etc. That is, the expansion moves space, not moves objects through space. The same kind of idea that if you entered a (theoretical) wormhole you are not moving through space faster than light, you are just moving from one point in space to another point, with very little relativistic movement.

[astromark]

Dark energy, in all its forms, works through gravity, it is not an opposing force.

Where did you get this ? That would not be right. It would seem to me that it is most certainly not gravity. We have named it Dark Energy because we do not understand yet its driving force...

[Ken G]

I know this is bordering on ATM, but would the expansion also correlate to the theory of wormholes, folding space, etc.

I think you are right there, the basic idea is that general relativity allows space and time to be active players in dynamics, not just a passive "canvas" against which the dynamics is painted. So once time and space are allowed to be active players, they can do all kinds of strange things, like expand or make wormholes, etc. (though the latter has never been verified in an experiment, to my knowledge). It's what gives hope to FTL ideas, but nothing remotely close has ever been actualized by human engineering.

[Ken G]

Where did you get this ? That would not be right. It would seem to me that it is most certainly not gravity.

Actually, one leading idea for dark energy is that it is a "cosmological constant", which is a term in Einstein's field equations of general relativity (which is a theory of gravity). Whether one calls that gravity, or antigravity, or something different from gravity, is kind of a matter of semantics-- it shows up in the equations of gravity, if it is indeed best treated as a cosmological constant.

[island]

Everybody is right.

Einstein's cc is a counterbalancing force that has a negative pressure component, but modern ideas tend to do away with negative pressure. In this case, it is the positive gravitational effect of dark energy that is "pulling" the observed universe apart from beyond the event horizon.

In Einstein's static cosmological model, the Gaussian curvature of every two-dimensional tangent subspace has the same value at every point, and the four-dimensional space has zero Riemannian curvature, so it is said to be "flat". The "boundary conditions" are directly identified with the distribution of mass-energy, while the negative pressure component produces an "antigravity" affect, so that the normally cumulative gravitational effect is counterbalanced by the repulsive effect of the negative vacuum pressure. Misner, Thorne, and Wheeler noted that General Relativity requires closure of the geometry in space as a boundary condition on the initial value equations if they are to yield an accurately determined metric.

In General Relativity's most natural universe, the vacuum has negative density when, P=-u=-rho*c^2. In this static state, pressure is proportional to -rho, but pressure is negative in an expanding universe, and so energy density is positive.

The vacuum energy density is less than the matter energy density, but it is still positive.

[sirius0]

I think you are right there, the basic idea is that general relativity allows space and time to be active players in dynamics, not just a passive "canvas" against which the dynamics is painted. So once time and space are allowed to be active players, they can do all kinds of strange things, like expand or make wormholes, etc. (though the latter has never been verified in an experiment, to my knowledge). It's what gives hope to FTL ideas, but nothing remotely close has ever been actualized by human engineering.

I seem to recall some work in optics that involved a "wormhole" and later mathematical speculation that this could lead to 'cloaking' devices some day.
I will try to find a link....

[Ken G]

I'm pretty sure no one has ever opened a true GR-style "wormhole" in any experiment of any kind. Perhaps there is some kind of optical analogy...

[Kwalish Kid]

Einstein's cc is a counterbalancing force that has a negative pressure component, but modern ideas tend to do away with negative pressure. In this case, it is the positive gravitational effect of dark energy that is "pulling" the observed universe apart from beyond the event horizon.

The "pressure term" of the vacuum density is somewhat analogous to the pressure of ordinary matter, but it isn't exactly the same. Regardless, it is still negative if we assume certain equalities between different reference frames.

The action of the cosmological constant or the vacuum energy is not pulling form beyond an event horizon, it is a gravitational effect with a sign the opposite of that associated with normal matter and energy. So within a given volume, that density influences test particles to diverge from the centre of the volume rather than converge on the centre of the volume.

[astromark]

A key hole is a hole in a door that you could shine a light through... but should be used for the key.
A worm hole is often found under or near a worm mound...
I will not have it said that the expansion of the universe is antiegravity. It would seem to me that antiegravity is a science fiction idea that would to me be entirely neutral to gravity, exempt if you like... not the opposing force. Which has a name... Its called Dark Energy. Can we not just except that as yet we have not the information required to answer this any other way. Speculative propositions are not as yet fact proven.

[island]

The action of the cosmological constant or the vacuum energy is not pulling form beyond an event horizon, it is a gravitational effect with a sign the opposite of that associated with normal matter and energy. So within a given volume, that density influences test particles to diverge from the centre of the volume rather than converge on the centre of the volume.

Well, okay, but I think that I heard Sean Carroll going on about a paper that he co-authored, in which it worked the way that I described it, (maybe I misunderstood), but since nobody knows exactly what dark energy is, I guess that all possible solutions are viable as long as they also fit with theory and observation.

The way that you speak of opposite sign is typically associated with negative mass... speaking of lame ideas.

There is a real simple way to grasp this with the classical rubber sheet analogy for the space-time metric, where G=0 when there is no pressure and also when the gravity of matter is absolutely offset by negative vacuum pressure.

Einstein brought in the cosmological constant to counterbalance the runaway re collapse effect that occurs in this model because of the obvious fact that we do have matter, but in order to get rho>0 from Einstein's matter-less spacetime structure, you have to condense the matter density from the zero pressure metric, and in doing so the pressure of the vacuum necessarily becomes less than zero, P<0, which causes expansion via vacuum rarefaction.

*Note that the mass-density of the finite background changes every time that you do this due to rarefaction of the mass-energy that comprises the vacuum, while vacuum expansion accelerates without instability because it takes a greater volume of the vacuum to attain enough mass-energy to make a real, massive particle.

Einstein didn't introduce the counter-balancing cosmological constant with matter generation from the vacuum in mind, so he didn't like it, because without this knowledge he naturally concluded that it added an undesirable extra entity, so the logic that was used to reject the cosmological constant when it was discovered that the universe is expanding was sound in context with the knowledge of the time, but this is not the case given knowledge that the vacuum has real, massive, particle potential.

I don't think that it is at all speculative to say that the most natural way to create new matter in Einstein's model, ("the most compatible with the spirit of general relativity"), also holds it flat and stable, (it is "self-guaging"), so any other conclusions that have been made since Einstein abandoned his finite universe without this knowledge are therefore subject to review.

[Kwalish Kid]

While the hypothetical matter creation fields offered by different theorists do act essentially as a cosmological constant, neither the cosmological constant nor dark energy is associated with matter creation. The activity of these (mathematically equivalent) parameters is to change the geometry of spacetime through the Einstein Field Equation. These parameters have these features regardless of the reasons that Einstein had for introducing and rejecting the cosmological constant.

I suspect that Carroll was discussing the possibility that some of our tests for the presence of a non-zero cosmological constant could be mimicked by a peculiar distribution of matter in the universe: the visible universe we see could be less dense than the space surrounding it. Thus the attraction of the dense space surrounding our effective horizon could influence the scale factor within our horizon.

[island]

While the hypothetical matter creation fields offered by different theorists do act essentially as a cosmological constant, neither the cosmological constant nor dark energy is associated with matter creation.

That doesn't change my point in context with the cosmological model that I was referring to. The dark energy of Einstein's finite model cannot be disassociated from matter creation, period, end of story.

[Ken G]

Einstein didn't introduce the counter-balancing cosmological constant with matter generation from the vacuum in mind, so he didn't like it, because without this knowledge he naturally concluded that it added an undesirable extra entity, so the logic that was used to reject the cosmological constant when it was discovered that the universe is expanding was sound in context with the knowledge of the time, but this is not the case given knowledge that the vacuum has real, massive, particle potential.

The reason Einstein ended up disliking the cosmological constant had nothing to do with his not understanding matter generation, it was for two much clearer reasons:
1) Einstein's whole purpose for introducing the cosmological constant was to allow a static universe, but it failed that purpose anyway, because it would not have been a stable static universe, and
2) had Einstein simply believed his own equations, he could have theoretically predicted that the universe was fundamentally dynamic, i.e., either expanding or contracting, even before its expansion was observationally discovered.
Put those two together, and he must have been kicking himself from here to Timbuctou. It is too bad he missed the final act of the whole ironic saga-- dark energy.

[Kwalish Kid]

That doesn't change my point in context with the cosmological model that I was referring to. The dark energy of Einstein's finite model cannot be disassociated from matter creation, period, end of story.

I'm not sure what story you are referring to, but I do know that the story is fictional. Einstein never used dark energy, he used a cosmological constant. Nor did that cosmological constant play any role in the creation of matter. Matter was neither created nor destroyed in Einstein's initial cosmological model.