The discussion revolves around the necessity of inflation in explaining the uniformity of temperature across the universe. Participants explore whether there are compelling reasons for different regions of the universe to have been at different temperatures initially, and whether inflation provides a necessary mechanism for achieving uniformity.
Participants do not reach a consensus on whether inflation is necessary to explain uniformity. Multiple competing views remain regarding the initial conditions of temperature and the mechanisms involved.
Participants express uncertainty about the mechanisms that would lead to temperature differences without inflation, and there are unresolved questions regarding the role of quantum fluctuations in this context.
The problem is that there is also no convincing argument that different parts should be at the same temperature. In inflationary models, there is a convincing argument that they should.Green dwarf said:But I've never seen any reason why the different parts should have been at different temperatures in the first place. Is there a simple answer to that?
That's ok, but is there any convincing argument that they should be at different temperatures without inflation? If there's no argument either way, then inflation might seem not to be necessary.Orodruin said:The problem is that there is also no convincing argument that different parts should be at the same temperature.
Couldn't one say that being at different temperatures without some mechanism would be just as unexpected?mathman said:Being at the same temperature without some mechanism would be an unusual coincidence.
No. See Bandersnatch reply.Green dwarf said:Couldn't one say that being at different temperatures without some mechanism would be just as unexpected?
When you roll a die, it has equal probability of showing any of the six numbers, so one would expect variation. But all parts of the big bang fireball were produced in exactly the same way, so I can't see why one would expect variation there. What is it about this part of the fireball that is going to cause it to have a higher temperature than that part? The only mechanism I can think of is quantum fluctuations, but, as far as I understand, we see these preserved in the microwave radiation, not eliminated by inflation. Maybe the quantum fluctuations before inflation would have been much larger relative to the size of the universe at that time and so inflation is necessary to eliminate these. I don't know. This is what I'm asking.Bandersnatch said:If you had a hundred dice, rolled them, and all ended up showing 6s, would you be arguing that this is just as unexpected as a random spread of outcomes?
As you roll back the time in the big bang model, any two causally connected regions eventually become disconnected. Each point in space becomes an independent die that doesn't know of the existence of any other dice. When you're thinking something like what you said here, you're implicitly assuming the existence of some mechanism that made all the disconnected parts of the universe in some way connected (made all the dice loaded), without specifying what that mechanism was. There's not enough to just say there was some fireball that created everything equal (what made it 'know' what equal means?).Green dwarf said:When you roll a die, it has equal probability of showing any of the six numbers, so one would expect variation. But all parts of the big bang fireball were produced in exactly the same way, so I can't see why one would expect variation there. What is it about this part of the fireball that is going to cause it to have a higher temperature than that part?