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Comment by aedanman | Hacker News Reader

There are far fewer *Visible stars and galaxies than we thought

This is more about the invisible stars and galaxies, the ones too far to actually count, but whose lights just gives a faint glow to the darkness.

This depends on your definition of visible. If you think of visible as some form of light reaching a man-made object, then GPs statement is still true.

Well, stars whose light has never even reached us are likely out of our light hypercone, so they might not exist in the scientific sense (i.e. Their existence or non-existence is completely unprovable and has no consequences, even in principle).

I know this is goofy, but it would certainly have consequences if this realm of space contained an advanced civilization capable of reaching us before the light did.

If the theory of relativity is wrong, than yes, absolutely, the notion of a light hypercone is wrong as well, and the notion of what is within the realm of science changes.

Isn't this like saying that aliens do not exist, because we never received any signal from them? Of course you can see it like that, but does it really change the probability of their existence?

I think there's a difference between what we know and what actually exists.

Well, if the aliens exist outside our light hyper-cone (that is, by definitio, any kind of information from them has never reached and will never reach any piece of information we create) then it is the same.

However, if any aliens have lived or will live anywhere in the visible universe, then that is something we could at least in theory confirm our deny at some point, so it is not the same.

It's also important to remember that time is relative - that is, that events in far away places don't happen at a definite time compared to those happening here. That makes their existence different to me than what we normally think of as existence.

Existence has two senses anyway - one is the empirically verifiable bottom of existence that science can work with: this is the one I was referring to.

The other is a philosophical notion of existence that is harder to pin down. In this sense, God may well exist, the nultiverse with many big bangs may be real, infinity may be real etc. But it is impossible right now to make any kind of scientific arguments about these things, so they can only exist outside the realm of science (as we know it today).

You introduced "will never" to this argument here. Neither me nor parent comments said that being visible today or in the past has anything to do with being visible in the future.

I would argue that science is about a core of what is considered proven and thus is true, as well as topics that are currently discussed and a large amount of knowledge that still has to be discovered. And I think these galaxies that are invisible today might be in the latter category - if they exist at all. But I wouldn't rule out their existence unnecessarily. In a few years, due to advances in technology, it could be possible to "discover" (or rather estimate) far more galaxies than what is proposed in this study.

Just because mankind in the middle ages had never seen Pluto doesn't mean it didn't exist back then.

The thing is, given the accelerating expansion of space in every point, it is likely, as I understand, that light from any star distant enough that it hasn't reached us yet will in fact never reach us.

I would argue that any reasonable definition of visible includes being able to resolve features. In support of this, many dictionary definitions include words like 'accurate', 'clear' and 'obvious', while it's antonyms include 'unclear', 'indistinct' and 'obscured' and not just 'invisible'.

> So, what could be the source of this leftover glow? It’s possible that an abundance of dwarf galaxies in the relatively nearby universe lie just beyond detectability. Or the diffuse halos of stars that surround galaxies might be brighter than expected. There might be a population of rogue, intergalactic stars spread throughout the cosmos. Perhaps most intriguing, there may be many more faint, distant galaxies than theories suggest. This would mean that the smooth distribution of galaxy sizes measured to date rises steeply just beyond the faintest systems we can see – just as there are many more pebbles on a beach than rocks.

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