I was watching a program that described a hypothetical end to the universe,trillions of years in the future where all the atoms decayed, and even the black holes decayed, leaving the 'big chill'.
Space and time would still exist, would it not ? What would happen if such an environment had an expansion of energy/matter into it.. sort of a 'big bang 2'. How would observers in that 'second big bang' see the universe differently than we do now?
How can we distinguish between expanding into an empty, cold universe that already had 'space' and distance, versus the creation of space/time as the inflationary theory of the big bang says? If, after a bunch of billion years, intelligent creatures evolved, .. how would they know they were part of an older universe that 'chilled out' .. or would it appear to them that space/time formed at the beginning of the expansion of their energy/matter?
Edited by Adminnemooseus, : Changed topic title from "The begining of space/time and the big bang" to "Big Bang 2 and a new beginning of space/time".
I originally sent this suggestion to Ramoss as a personal message, but I now think it should be in the topic itself.
Quoting my PM:
Message 1 looks pretty good, but I suggest a topic title change.
Instead of the existing "The begining(sic) of space/time and the big bang", how about "Big Bang 2 and a new beginning of space/time"? Maybe that would help distinguish your topic from the many Big Bang topics that have already happened.
An interesting idea and one dealt with in the scientific literature.
First of all I assume that you do not mean matter expanding into a pre-existing space. This can be easily distinguished from our current universe as the motion of matter is not driving the expansion between the galaxies (easily seen to be true as the galaxies show no effects of acceleration).
So I will take you to mean to the following scenario. That there was already space and in a small region of that space some ball of matter began to cause the space in which it existed to expand rapidly (i.e. its section of the larger universe began to expand).
The problem with this is very simple. You simply can't have that amount of matter compressed in a pre-existing universe and then have it expand. Einstein's General Relativity (or even alternate theories of gravity like Brans-Dicke) just don't predict that a ball of matter would evolve like that in pre-existing spacetime. Rather it would collapse in on itself.
Well, wouldn't it be a highly compact amount of energy, rather than matter? Didn't it take a certain period of time for even sub atomic particles to form?
Energy is just a property of matter, not a thing itself. Early in the universe matter wouldn't have been organised into states that we'd recognise as particles, but it was still matter, highly compressed matter.
Could you point me to an essay or article on it??
On what specifically?
And I thought that the far galaxies DID show effects of acceleration.. as measured by the Ia supernovae in them.
They show effects due to the acceleration of the expansion of the universe, but they are not really moving themselves, rather the space they exist in is expanding.
Salient point being the conservation of information is preserved in the latter theory.
It seems more plausible that eventually everything will be so spread apart that even light will not reach the observer. The universe will possibly just go dark. Things happen because there are differences. If nothing interacts, nothing happens.
"You were not there for the beginning. You will not be there for the end. Your knowledge of what is going on can only be superficial and relative" William S. Burroughs
I am beginning to see, through a glass darkly. However , if gravity causes space to bend, why didn't the matter cause the space to bend rather than 'inflate'??
Matter doesn't really cause space to bend. Rather matter determines what the geometry of spacetime will be.
More specifically the energy density of matter at a point added to the flow of momentum caused by the matter at that point determines the part of the curvature of spacetime which causes balls of particles to shrink over time (The volume shrinking curvature). More detail in this post: Einstein's Equations
Although you can mathematically calculate the spacetime geometry which results from a piece of matter, there isn't really an intuitive way to guess at what it would be like.
For a spherical ball of matter like the Sun the result is something you could call a bending of spacetime (mostly time in this case).
For a homogeneous gas (like the universe on the largest scales) the result is a spacetime where space expands as time passes.
Is that one of the things that 'dark energy' is responsible for, since the expansion of space is accelerating?
In the post I link to above I give the Einstein's equations as:
The term on the right is completely fixed, it is the energy and momentum flow density of matter. On the left-hand side you have a term related to the geometry of space. In this case , called the Einstein Tensor. The Einstein Tensor measures the volume shrinking part of curvature.
You can't just put any geometric term on the left hand side, as Einstein realised, since most geometric quantities "diverge". This basically means that they can grow in value at a given point without being compensated by a decrease at another point.
which measures the matter, never diverges (new matter can not just "appear" without a compensating loss of matter elsewhere). So only divergence-less geometric terms can be used, since only they will match the behaviour of .
This really restricts the choice of what can be on the left-hand side, down to pretty much just:
In this equation is just a number and is the metric, a geometric term describing how distances work in the spacetime.
Einstein, and most people after him had no idea what value should have. So in most textbooks on general relativity and in research up until the late 90s it was largely ignored and instead we used the equation given above:
This is because the results in most cases aren't really that different. For instance the shape of the spacetime around the sun is virtually identical under the two equations (unless is unrealistically large).
However for a homogenous cloud of gas (like the universe on the largest scales), the two equations give quite different results. The simpler equations give an expanding universe, however the equations with a positive give an accelerating expanding universe.
Then basically in 1998 we found that observations of distant stars in our universe match the universe described by the equations with a very small positive .
Now the question is: why does have the value it has?
There are several different proposals, we just call all of them "Dark Energy", because has units of "joules per volume", i.e. units of energy density.
I should follow up on the previous approach and attempt to say what exactly is Dark Energy, or rather the two most popular ideas. There is some very bad information out there on this, so I want to carefully explain the two ideas.
Vacuum Energy: This is probably the most basic, least exotic guess at what Dark Energy is. In the previous post I wrote the Einstein's equations as:
However the matter here is classical, but we know matter is quantum mechanical. We don't know if spacetime is quantum mechanical (and if it is we don't know how to describe it, that's the problem of quantum gravity). So, to improve this equation in a way consistent with what we know already we make matter quantum mechanical, but keep gravity classical. Since matter is now quantum mechanical it is probabilistic. Hence, has no definite value and fluctuates. However, gravity is still classical and deterministic, so it cannot interact directly with something fluctuating like this. We need it to interact with a deterministic quantity. Fortunately the average stress-energy is deterministic. (Averages are always deterministic in quantum mechanics and behave classically. Also by average I mean that the quantum matter will have a stress-energy that jumps all over the place, but is the central value about which it fluctuates.)
This leads to the naive semi-classical gravity equations:
These are naive, since if you try to solve the equations you get infinities. This is the problem known as renormalisation. Quantum theories often have infinities if you use the exact same equations as the classical theory. Generally these infinities only disappear when you add new terms to the equation. Basically the quantum theory requires new terms.
It turns out the infinities only vanish if you add two new terms to the equation:
Two interesting things here:
Even if I'd started with no cosmological constant, like:
I would still have ended up with:
in order to remove the infinities. Even if I start off with no , it's automatically generated when I try to get rid of the infinities. That is Quantum matter requires the cosmological constant. So we at least know why it isn't zero.
The new terms:
are geometric terms describing how curvature changes as you move through spacetime. ( are just numbers) At first people found them a bit odd. They make the equations much harder to solve and they're not "natural" quantities by which I mean, aside from removing infinities, they don't seem to have a physical explanation. However they were later discovered to have a very important effect, they make spacetimes containing time-machines impossible. The old classical equations:
can give rise to time machines with the right on the right-hand side. This can never happen under the new equations:
Quantum matter does not allow time machines.
There are a lot of things making up :
The first is the part coming from when you try to remove infinities that the theory would have even if there was no matter, i.e. infinities that are there even in a vacuum. This is .
The second part is called (ind=induced). This part comes from infinities relating to: The masses of the W and Z weak bosons The strength of the Higgs field The energy where left-spinning and right-spinning quarks behave the same The energy where the electroweak force separates into the electromagnetic force and the weak force.
I'll stop here and continue in the next post because it looks a bit less cluttered.