Re: Model describes universe with no big bang, no beginning, and no end.
 

This isn't entirely true. For the most part, theories that predict an infinitely aged universe would violate the second law but it is possible to construct ones that don't. That is, over an infinite amount of time the change to entropy is finite (I think the best way to think about this is like a convergent infinite series - the sum of infinite finite numbers can give a finite number). In this manner it is possible to imagine a universe that obeys the second law but has infinite age.

Re: Model describes universe with no big bang, no beginning, and no end.
 

You'll have to elaborate on this for me.

Should that be the case, what was the big bang exactly?

Black Holes are interesting, but not infinite.

If a larger black hole were to come across a smaller black hole, I believe that the larger one would 'consume' the smaller - this does not mean that the larger one would grow in size. It would remain the same.

As for a Black Hole being all that is left at the end, I do not think so. There are always going to be Stars dying and being born, I expect in larger numbers too (especially if the universe is expanding). When a star dies, it'll either explore, potentially creating x number of other stars in it's wake, or it'll implode, and become a black hole.

So long as there is a Universe out there, I believe that stars will forever continue to do this, and with new stars come new rocks, and with new rocks come new planets, and with new planets, comes new life.

It's everlasting. I'm guessing only some small portion of this life will ever 'make it to the stars' as we put it today. Think how many species of animal have been on this very planet, yet haven't made it across continents, yet alone to the moon or beyond.

My Head!!!

Re: Model describes universe with no big bang, no beginning, and no end.
 

Well, because the age of the universe is infinite, and entropy increases with any action in a closed system, assuming the universe is a closed system, then by the time we've come along, entropy would be infinite and everything would be a homogenous soup of particles floating around.

So...change to entropy over time decreases and tends towards a finite value...? If you were into designing universes, how would you make this happen?

Re: Model describes universe with no big bang, no beginning, and no end.
 

[QUOTE=Aerilon;5379864]You'll have to elaborate on this for me.

Should that be the case, what was the big bang exactly?



Erm, a big bang.....
What makes it law that time MUST start with the big bang, we simply cannot tell if time started with the big bang or before it.
l would argue for any action/re-action to occure, time must already be in motion, something caused the big bang to actually go bang, without knowing what elements were involved all were left with is the hypothesis that time may have been there.

PS.My understanding of blackhole is that if one eats another it gains MASS, ie it gets bigger, in the end of time as we know it, all that will be left is blackholes, is one theory, more mass , more gravitational pull, its a bigger blackhole, also, the blackhole at the centre of our gallaxy is the biggest one we have seen, far bigger than others seen.l think your wrong about blackholes.

Re: Model describes universe with no big bang, no beginning, and no end.
 

Good question.
So I guess the best example to use would be a (hopefully) familiar one. I imagine at some point you will have come across the gaussian (or normal) distribution. This serves as a good example for what I was trying to get across, as while at any point in (x) the function:
http://upload.wikimedia.org/math/9/e...9a0b69fbf6.png
has a non-zero value. This is because functions like:
http://upload.wikimedia.org/math/a/d...af5e2fd5ae.png
only decrease with (x) and never reach 0.

This further implies that while the normal distribution has a non-zero value for ALL values of x, the integral of it (i.e. the total area under the curve) is, something like:
http://upload.wikimedia.org/math/5/1...8716ed9d38.png
Which if we set x to +infinity is = 1.

This is the sort of property we would require of the change in entropy (as a function of time) if we were to allow "x" (i.e. time) to go to -infinity without violating the second law (i.e. the integral remaining finite).

Now, onto how I would achieve this. I would postulate the existence of a [url=http://en.wikipedia.org/wiki/Scalar_field]scalar field[/quote] that acts as a "fluid" in the friedmann equations which describe (roughly) the expansion of the universe. In these equations all "matter" in the universe is described as a "fluid", and we can evolve the size of the universe (and other values like entropy) with time. I would "design" this scalar field to allow the universe to have an infinite age and still match up with current observations and established values. To actually "evidence" this I would have to use the inclusion of this scalar field to make a prediction about the universe and its behaviour.

Hope that (roughly :) ) helps.

Re: Model describes universe with no big bang, no beginning, and no end.
 

yea ok, erm, what ?

Re: Model describes universe with no big bang, no beginning, and no end.
 

He asked me how I would go about it (if I were into designing universes, which in a way I was). That above is how I would go about it, with no real detail. It's sort of difficult to explain without a massive post.

Re: Model describes universe with no big bang, no beginning, and no end.
 

Yea l got that, hence the, whaaaaaaaaat ? hahaha

Re: Model describes universe with no big bang, no beginning, and no end.
 

So entropy is the integral...so what becomes the derivative of entropy? I know it wouldn't need any physical 'manifestation', but what would it be?

So in essence depending on the size of the universe, then the physical constants in that universe would change also; so they'd be constants still, in the sense that we would not be able to change them, but they would still be able to change? Wouldn't that, over longer periods of time, cause quite an 'interesting' universe? For example, if the gravitational constant kept changing, then wouldn't the velocities and orbits of all the planets, galaxies, etc. change as well? Or wouldn't satellites just crash into their host bodies? (I don't know if gravity in this way works in a positive or negative feedback system).

Isn't that what the original paper is proposing? An infinitely old universe with changing physical constants coupled with oscillating periods of expansion and contraction?

Re: Model describes universe with no big bang, no beginning, and no end.
 

This is effectively what's been done yes. The models don't necessarily require variable "constants" of nature as this one uses, but it is becoming a more and more common feature.

Interesting to read on a similar vein would be "Joao Magueijo: Variable Speed of Light Theory (VSL)" or the "pop-sci" book he wrote "Faster than the speed of light" (from memory). In any case that and "the first three minutes" by Weinberg serve as a decent coffee table physics read :)