Comment by misja111 | Hacker News Reader

Comment by misja111 | Hacker News Reader

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This isn't comparable to evolution theory where we have mountains of evidence of other species that were predecessors of the current ones. Or where we even have evidence of evolution happening during our lifetimes (e.g. Covid). The Big Bang theory is extremely speculative.

Empirical Science is about building theories based on observations. We have no observations that provide any kind of evidence that there was a big bang. Yes, we now that the universe is expanding, and has been for quite a while. So reasoning backwards, there must have been a time that the universe was a lot smaller than now. But that's it. We don't know how small it was before it started expanding. Maybe our universe started from a single point or even from nothing. Or maybe it bounced back after having contracted to a small but definite size. We just don't know. And actually, with the recent JWST observations, hints that support a big bounce or something similar are building up.

I don't have the scientific background to really argue with you on this; I'm just an enthusiastic amateur.

That said: Big Bang does explain an awful lot of stuff. I'm not sure what JWST observations you say call it into question, but wouldn't we need a lot more data before advancing Big Bounce or something else as an alternative?

As long as there is no direct evidence supporting the Big Bang theory, any other alternative is equally good IMO.

The JSWT observations putting some doubt on the Big Bang theory are the observations of very old galaxies. E.g. one was observed at a time that the universe was only 250 million years old (according to BB theory), really not much on a cosmological time scale. The thing about this galaxy was, that it seemed like a pretty normal galaxy already. Which makes people wonder how it could have formed so quickly.

Another observation casting doubt on the Big Bang theory is the (indirect) observation of some very early massive black holes. Again the question is how they could have formed so fast.

Well, ok. If direct evidence is what you want, cosmology is generally lacking in that. We're here, now, and nothing is going to change that.

@UIUC_06: sure, I agree. The lack of direct evidence is more often a problem in cosmology. Some even refuse to call cosmology a science because of that. But if all of them are speculative, then why refuse any other theory than the BB theory in arxiv?

> The Big Bang theory is extremely speculative.

There is no other plausible explanation of the cosmic microwave background radiation.

This doesn't make it less speculative. What would is to incorporate less assumptions or to prove some its assumptions with practice.

I like speculativity very much, it's just a note on it.

The CMBR requires the existence of a dense, optically thick, hot state early in the universe. That's pretty much the Big Bang. There's nothing speculative about that, it follows from rather simple physics.

But anyway, give an alternative model that explains it. I'll wait.

It's pretty much the Big Bang but not quite. The Big Bang theory claims more than that: it claims that our universe started from nothing or from a single point. It needs some fancy new physics to explain our current universe from that: e.g. hyper inflation.

There are some alternatives to the Big Bang theory, e.g. the Big Bounce. This also claims the existence of a thick hot early state, but a bit more than a single point. This theory also explains cosmic background radiation.

No, the Big Bang doesn't assume the universe started from "a single point". Nor does it assume inflation. The Big Bang theory doesn't even go back to t=0. It leaves unspecified what happens at very early times. The BB is compatible with inflation, but theories of inflation were proposed well after the BB theory itself.

I didn't say the BB assumes inflation, I said it needed fancy physics such as inflation to explain the current state of the universe.

> The BB is compatible with inflation, but theories of inflation were proposed well after the BB theory itself.

Exactly, and the reason these theories were proposed was to 'fix' the BB itself. So of course they are compatible with the BB. There is no observation that asks us to consider something like hyper inflation, except if you assume that there has been a BB.

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