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Comment by waterlesscloud | Hacker News Reader

We barely know anything about cosmology at all, when you get down to it.

Why do you say that?

Because there are so often things we discover we're fundamentally wrong about. It's really a pretty thin science based on a lot of assumptions and inferences.

It's very safe to say most of what we know about cosmology is wrong, and a large portion of it is probably deeply wrong.

I would imagine cosmologists know where the boundaries are between what we know, what we don't know, what we "might know" (i.e. the status of various hypotheses and theories with regards to supporting evidence). I think it's safe to say that there is a lot of stuff in each of these categories.

It would be pretty surprising if we're "fundamentally wrong" about cosmology, given that scientists are aware of what goes where, with respect to these categories. Plus, I'd imagine a lot of cosmology is purely observation, anyway, and you can't be "wrong" about observation.

There is a lot of room between "omniscient" (which many people mistakenly demand of science) and "wrong". In other words, science can and must deal with partial knowledge.

Cosmologists have pretty wide agreement on, for instance, the order of events in the first second. See http://en.wikipedia.org/wiki/Inflation_%28cosmology%29 for details.

Those events took place under conditions of gravity, temperature and pressure that we can't reproduce.

Those theories include belief in a phenomena called inflation which is not predicted by any theory we have in physics today, and which has some internal contradictions. (See http://www.edge.org/q2008/q08_4.html#Steinhardt for an explanation of some of them.)

Oh, and the thing we can look at to test these theories? That's the cosmic background radiation which is believed to have been formed several hundred thousand years later.

Are you still confident in what scientists currently claim about cosmology?

That's the thing, it's mostly all stuff we "might know". And most of the observations are based on a lot of assumptions and inferences. It's not like "how much liquid is in this vial". The measurements and observations depend on a chain of things being true that might not be true.

Seriously, what are you talking about?

We know a lot about cosmology. In particular there is very good evidence for for the basic model: hot big bang, cold dark matter, accelerating expansion, geometrically flat, ~14 billions years old (see http://www.astro.ucla.edu/~wright/cosmology_faq.html for more).

Granted we don't know what the dark matter is, and we don't know what's causing the acceleration. Those are big unknowns! But the basic picture is pretty well understood. And I think it's very unlikely that much of this picture is "deeply wrong".

I mean, what do you think? Some day we are going to discover that the universe wasn't really denser and hotter in the past? That the universe isn't really expanding? That baryonic matter makes up all of the mass of the universe?

The very faq you link to uses cautious language. Look at "currently most accepted model" right there in the first question.

If you've followed cosmological history at all, it's been a cascading series of big changes decade after decade.

I'm virtually certain the model of 2030 will vary in deep, significant ways from the model of 2010.

Can you be more specific? What parts of the "hot big bang, cold dark matter, accelerating expansion, geometrically flat, ~14 billion years old" model will be shown to be "deeply wrong"? Do you think that discovering, say, the nature of dark energy, is going to demonstrate that the universe isn't really expanding? That we are going to discover that the universe is really 100 billion years old? That the universe was actually colder and larger in the past?

You're both correct. We know a lot about cosmology compared to what we knew, say, 100 or especially 200 years ago. Many of the big, open cosmological questions throughout human history (what is the Universe, how was it created, how old is it, what are the stars, what powers the stars, how far away are galaxies, etc, etc) have been answered.

We should not downplay that remarkable achievement. We know the age of the Universe to high precision, despite the fact that that age is fully 6 orders of magnitude greater than all of human history.

Nevertheless, there is still much we don't know, and likely what we don't know easily exceeds what we do know, by a fair margin. We do not know the nature of the majority of dark matter, we do not know the nature of "dark energy", we do not fully understand why the Universe is filled with matter rather than just energy, etc.

waterlesscloud is not saying that there is lots we still don't understand. He is saying that much, perhaps most of what we currently believe is "deeply wrong". This is of course possible, but I think it is very unlikely.

There is a big difference between saying that our current model is "deeply wrong" and saying that our current model might be superseded by a later model which encompasses the current observations. Therefore the major assumptions of the current cosmology are not likely to be "deeply wrong" anymore than Newton's theory of gravity was "deeply wrong" just because it was superseded by general relativity.

I do believe that our current understanding of cosmology has hardly scratched the surface of describing how things really are. However, any future model is not going to invalidate current observations, but rather, better explain them.

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