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?
Inflation is a theoretical concept in cosmology that proposes the rapid expansion of the universe in its early stages. This expansion is thought to have smoothed out any irregularities or variations in the distribution of matter and energy, resulting in the uniformity we observe in the universe today.
While inflation is a commonly accepted theory in cosmology, it is not the only explanation for the uniformity of the universe. Other theories, such as the anthropic principle and the multiverse theory, also attempt to explain this phenomenon.
Inflation is believed to have created small quantum fluctuations in the early universe, which were then amplified and stretched out as the universe expanded. These fluctuations eventually led to the formation of galaxies and other large-scale structures we see in the universe today.
Currently, there is no direct observational evidence for inflation. However, scientists are actively searching for signatures of inflation in the cosmic microwave background radiation and other astronomical data. Additionally, experiments such as the BICEP2 telescope have claimed to have detected evidence of inflation, but these results are still being debated and further research is needed.
While inflation is a widely accepted theory, there are still some challenges and criticisms. Some scientists argue that inflation is too complex and requires too many assumptions to be considered a valid explanation for the uniformity of the universe. Additionally, the lack of direct observational evidence for inflation is a major criticism of the theory.