Comment by AnonC | Hacker News Reader

Comment by AnonC | Hacker News Reader

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I’m not an expert on this, but I read this by Lawrence M Krauss (theoretical physicist and cosmologist):

“In 5 billion years, the expansion of the universe will have progressed to the point where all other galaxies will have receded beyond detection. Indeed, they will be receding faster than the speed of light, so detection will be impossible. Future civilizations will discover science and all its laws, and never know about other galaxies or the cosmic background radiation. They will inevitably come to the wrong conclusion about the universe......We live in a special time, the only time, where we can observationally verify that we live in a special time.”

A billion is just 10 to the power of nine, and that number of years in time is itself a long, long time that’s difficult to imagine. Looking at 10 to the power of 78 is…it wouldn’t matter much for us if it were to the power of 60 either. (I think!) I seriously doubt humans (as we know of now) can meaningfully affect the expansion or decay of the universe.

In just 5 billion years? This surprises me, trillion I could understand, 5 billion is similar to the age of the earth.

Incidentally, the obvious counter to "our time is special, we have access to everything" is presumably what future civilisations think as well; the implication being perhaps we have lost something over the aeons that would shed light on our current mysteries.

I haven't read the book but it's an unconvincing extract, though I acknowledge a larger context may justify it.

Someone made a miscalculation with 5 billion years, but with that said, it's only just over an order of magnitude more which isn't much

>And what are presently the closest galaxy groups outside of the Local Group — objects like the M81 group — will be the last to become unreachable: something that won't occur until more than 110 billion years from now, when the Universe is nearly ten times its present age.

Maybe there was a self-conscious "civilization" before the big bang. From my understanding we know very little to nothing about anything before the big bang.

If the big bang created space and time, "before the big bang" is not really well-defined.

Unless you believe that this universe is just playing out holographic on the event horizon of an N+1d black hole in our parent universe. The Big Bang was just the singularity birth of that one object.

From inside that universe there still was no "before". Are you looking into our universe from the outside? ;)

Except not all dimension numbers have nicely defined physics and geometries. For example, 4+0 and 4+1 don't have symmetric pairwise particle interactions in the sense we have in 3+1.

It's going to get really irrational if we discover that the universe is only 2.71828... + 1 dimensions.

Can you provide the source for that quote? 5 billion years seems way too soon.

The Hubble constant is currently approximately one doubling per 14 billion years [1]. So 5 billion years isn't enough to double the recession speeds. AFAIK there's plenty of galaxies receding at less than half the speed of light. Wikipedia estimates 150 billion years (6000x expansion) for all but the local group to be beyond the horizon [2]. So your quote seems to be off by two orders of magnitude.

[1]: https://astronomy.stackexchange.com/questions/49248/interpre...

[2]: https://en.wikipedia.org/wiki/Timeline_of_the_far_future

> Can you provide the source for that quote? 5 billion years seems way too soon.

Yeah, seems off. According to Wikipedia it's 2 trillion years[1] until galaxies outside the Local Supercluster become undetectable.

[1]: https://en.wikipedia.org/wiki/Future_of_an_expanding_univers...

Which leads one to wonder what phenomena we were too late to observe and which of our assumptions are therefore faulty

Is that right? Only 5 billion years until noone sees the background radiation and other galaxies?!

That's... awe inspiring.

That seems relatively soon! I know it's a huge number, but on universal scales, that's crazy

Right so we're limited in time and resources, in a sense. Only some of the universe would be reachable within those 10^1100 or 10^78 years anyway. So we are limited by time but also what we can access.

What's fascinating to me is to consider the frontier of galaxies theoretically reachable within a given window, and the potential race to colonize them before they race away.

This is a good reason not to throw away your old textbooks.

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