B A question about which Cosmology theories are mainstream and how?

[Tanelorn]

TL;DR Summary

A question about which Cosmology theories are mainstream and how they become mainstream

I was reading recently about string theory recently which postulates that there are 11 dimensions representing all possibilities for everything. This is an interesting theory, although very difficult to prove and therefore somewhat speculative in my opinion. [Ed.: personal speculation removed] I move quickly to my question:

I would like to ask roughly how many professional Cosmologists are there, and who (and how) decides which Cosmology theories become accepted mainstream Cosmology? Is there an up to date resource for learning which Cosmology theories are currently the most accepted and which are hypotheses still require further investigation? Is there a professional body of Cosmology specialists who make a judgement on these matters?

[Moderator's note: If you know that personal speculation isn't allowed, why do you mention them? Post edited.]

 

[Arman777]

Look at the authors of these articles. These guys are in the field of cosmology
[2008.11284] Cosmology Intertwined II: The Hubble Constant Tension (arxiv.org)
There are four papers like this. But the authors are almost the same.

 

[kimbyd]

Summary:: A question about which Cosmology theories are mainstream and how they become mainstream

I was reading recently about string theory recently which postulates that there are 11 dimensions representing all possibilities for everything. This is an interesting theory, although very difficult to prove and therefore somewhat speculative in my opinion. [Ed.: personal speculation removed] I move quickly to my question:

I would like to ask roughly how many professional Cosmologists are there, and who (and how) decides which Cosmology theories become accepted mainstream Cosmology? Is there an up to date resource for learning which Cosmology theories are currently the most accepted and which are hypotheses still require further investigation? Is there a professional body of Cosmology specialists who make a judgement on these matters?

[Moderator's note: If you know that personal speculation isn't allowed, why do you mention them? Post edited.]

No single person makes such a decision. The science of cosmology (any science, really) is an ongoing conversation between scientists. No question is well and truly considered settled forever. Everything is open to criticism. But over time the answers that different cosmologists prefer tend to converge.

Scientists will generally ignore claims that aren't well-structured. This requires one of two things:
1) The claim is firmly grounded in evidence. The case of the Hubble tension is an example here: physical evidence that indicates that either our measurements are wrong, our assumptions are wrong, or our models are wrong. And the ongoing conversation between cosmologists will not come to significant agreement until there is lots of evidence.
2) The claim is well thought-out. This is a high bar to reach, often higher than many people seem to realize. It requires not only that people suggest something is different, but that they can describe it in a precise, mathematical way. It's not enough to say, for example, "Maybe gravity doesn't work like General Relativity says." You actually have to come up with a model that describes how gravity might operate instead.

Either of the above just get your foot in the door, though. These are the start of the conversation. The way the conversation continues for the first case is often a matter of gathering more evidence. Long experience has taught cosmologists that it is genuinely hard to find an observation that diverges from the standard model: nearly every observation which claims to turns out to be a false alarm. One of my professors liked to say, "I don't get out of bed for less than four sigma." Which is a way of saying that he wouldn't even consider an experimental deviation to maybe be real until there is overwhelming evidence.

Then, if an idea is to reach any kind of consensus, it's going to need to be tested against experiment. You can't just have an interesting, well-thought-out idea. There are lots of interesting ideas about how the universe might be. Determining which is the problem. Besides, ruling out things we haven't thought of yet is impossible. So if your theory can't be tested experimentally in some way, then cosmologists are never going to reach any kind of agreement on it. They might think it's plausible. Many might even think it's likely. But there will be many others who just discount it. Without observation, there's no way to obtain agreement.

String theory is instructive here. String theory sees a lot of attention primarily because it is extremely compelling in a mathematical sense. Perhaps the most compelling fact about string theory is that it predicts quantum gravity. Given that quantum gravity is the holy grail of theory in physics at present, this fact alone attracts a great many to it. String theory also predicts supersymmetry, which would neatly solve other problems in high-energy physics.

But string theory is incredibly difficult to test. The base model can never be tested for experimentally in any realistic sense: the energies required are far too high. There is always the hope, however, that we might get lucky and some of the models derived from string theory might be testable. Like supersymmetry. But we can't falsify the theory: the energy required is just far too high. If we get lucky, we might be able to confirm some aspects of it. But we would have to get lucky.

 

[Tanelorn]

Kimbyd, thanks for your reply.
String theory seems to me to be a mathematical description only and it may not represent what is actually happening physically, even if it outputs the correct numbers. In my work, where possible, I prefer observations, conceptualization, thought experiments, followed by modeling with representative simulations to better understand and represent reality. Although I do understand why this is difficult to impossible in the case of Cosmology.

Back to my original question, roughly how many scientists and experts are currently active in Cosmology and decide which theories are accepted mainstream Cosmology? Also are there more than one "camp" or group with somewhat opposing views forcing more rigorous analyses?

 

[kimbyd]

I have no idea precisely how many. Tens of thousands at least. And as I said, nobody decides. It's an ongoing conversation.

As for there being different camps, absolutely. But those camps tend to be very single-issue-focused. So you get people divided into dark matter and modified gravity camps, for instance (with the modified gravity camp shrinking, I believe). But they'll each have different views on different issues. You can't expect the MOND group to be in favor or against cosmic inflation, for example. Some will favor inflation. Some won't.

So there isn't, as near as I can tell, any sort of ideological division in cosmology. Not like in economics. Instead there is broad diversity of different topics, and how those topics should be approached. Overall, I think the system works pretty well. The diversity of opinion keeps cosmologists on their toes, and makes it easier to avoid getting stuck into a single line of thinking. Some always will get stuck in a single line of thinking, but the community as a whole does not.

 

[fresh_42]

The OP does not withdraw from discussing his personal views, and mocks moderation hidden between his explanations on the topic instead of citing reliable sources. Wikipedia is not.

Since the question has been answered and the OP is close from being banned from the thread, I will close this one now.