How does gravity affect the formation of structures after the big bang?

[Pengwuino]

I need some clarification on exactly (or not) how the big bang worked. If there was a uniform density of energy at t=0 (or whatever you want to call it) that began expanding at a uniform rate, how were things formed? It seems like if this were the case, everythings gravitational force would cancel out resulting in a failure for anything to form or they would form in some sort of fairly obvious pattern. Soooo... can someone explain what I'm missing here?

 

[Danger]

Only the fact that nothing in nature happens evenly. There are always random fluctuations in anything, and they interact in random ways. Eventually they (in this case energy densities) multiply to the point that any hope of regaining a homogenous distribution is lost.

 

[GOD__AM]

From what I understand distant objects were not effected by local EM radiation, or gravity until some time after the big bang. A time when those effects had enough time to propigate there.

 

[Lucretius]

If you want early timescales, you will need inflationary theory. The Big Bang does not answer the homogeneity question, but Inflation does an excellent job of doing so. It posits the cause of structure in the universe as the product of inflated vacuum fluctuations. These tiny fluctuations became gigantic as space itself expanded. The path of these fluctuations cut out an area that galaxies formed in.

I also would highly recommend not going to Kent Hovinds' website, unless you want to see what terrible science looks like.

 

[vanesch]

If you want early timescales, you will need inflationary theory. The Big Bang does not answer the homogeneity question, but Inflation does an excellent job of doing so.

Well, Penrose's not so enthousiastic about inflation solving this problem and I have to say that I find his argument convincing. The reason is that thermal equilibrium (high entropy) is NOT equivalent to homogeneity when gravity is taken into account. Homogeneity is a state of LOW entropy (far from thermal equilibrium) when gravity is taken into account, and as such, using a time-reversible mechanism such as inflation to explain a LOW-entropy situation does only report you to a _still more stringent_ condition before it. You cannot have "matter thermalize to give you a uniform distribution" on a small scale (unless you *switch off gravity*). If it were to "thermalize" (with gravity) it would generate lots of singularities, and that wouldn't give rise to a smooth uniform homogeneous structure after inflation. The only way inflation can give rise to a (low entropy) state of homogeneity is that there was a potentially even lower entropy state before it acted.
Now, I'm not an expert on this stuff at all, but I found this argument extremely convincing - although I can understand that it must be somehow controversial.

 

[Spin_Network]

I need some clarification on exactly (or not) how the big bang worked. If there was a uniform density of energy at t=0 (or whatever you want to call it) that began expanding at a uniform rate, how were things formed? It seems like if this were the case, everythings gravitational force would cancel out resulting in a failure for anything to form or they would form in some sort of fairly obvious pattern. Soooo... can someone explain what I'm missing here?

Taking what vanesch stated to be quite logical, one can ask the question what determines the scale of size in relation to Time?..Penrose has stipulated that as one reduces a system (the universe in reverse, has to arrive at a location smaller than a time dependant scale?), the reduced system undergoes a transformation from Macro to Quantum, Macro has Time and is thus Time-Dependant (GR), but you have to lose the Time componant in all reductionized systems, ie (QM-QCD).

Basically you cannot arrive at the big-bang, if it has evolution in TIME?..time-zero is really a SIZE of scale at a specific location.

 

[Spin_Network]

Taking what vanesch stated to be quite logical, one can ask the question what determines the scale of size in relation to Time?..Penrose has stipulated that as one reduces a system (the universe in reverse, has to arrive at a location smaller than a time dependant scale?), the reduced system undergoes a transformation from Macro to Quantum, Macro has Time and is thus Time-Dependant (GR), but you have to lose the Time componant in all reductionized systems, ie (QM-QCD).
Basically you cannot arrive at the big-bang, if it has evolution in TIME?..time-zero is really a SIZE of scale at a specific location.

This may be of interest? :
http://arxiv.org/abs/hep-th/0512070

and this:
http://arxiv.org/abs/gr-qc/0512034

 

[Chronos]

The answers are all [at least most of them] hidden behind the Planck wall. Physics, as we know it, ceases to exist around t = 10E-43 seconds.

 

[hellfire]

Well, Penrose's not so enthousiastic about inflation solving this problem and I have to say that I find his argument convincing. The reason is that thermal equilibrium (high entropy) is NOT equivalent to homogeneity when gravity is taken into account. Homogeneity is a state of LOW entropy (far from thermal equilibrium) when gravity is taken into account, and as such, using a time-reversible mechanism such as inflation to explain a LOW-entropy situation does only report you to a _still more stringent_ condition before it. You cannot have "matter thermalize to give you a uniform distribution" on a small scale (unless you *switch off gravity*). If it were to "thermalize" (with gravity) it would generate lots of singularities, and that wouldn't give rise to a smooth uniform homogeneous structure after inflation. The only way inflation can give rise to a (low entropy) state of homogeneity is that there was a potentially even lower entropy state before it acted.
Now, I'm not an expert on this stuff at all, but I found this argument extremely convincing - although I can understand that it must be somehow controversial.

This seams to be something profound but I cannot follow it... Black holes have a great entropy, but it seams to me that they are not the states of greatest (total) entropy because they do evaporate. When a black hole evaporates, it converts the Schwarzschild spacetime into another spacetime. What is the resulting spacetime? My first guess would be that it is a (expanding) space with a homogeneous distribution of radiation. In such a case, how can we say that homogeneity is a state of low entropy when gravitation is taken into account?