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Proving our universe is one among many would be a fourth Copernican revolution

nautil.us

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Re: Proving our universe is one among many would be a fourth Copernican revolution

#11

Post by lisper »

empath75 wrote: post #10
lisper wrote: post #9

Earlier quoted context omitted.

Well, yeah, but our perspective is the only one that can possibly matter for us. There may be unicorns and leprechauns out beyond our light cone for all we know, but what possible reason would there be to care?

What happens on the far side of the moon doesn't matter for us, either, but we still looked.

> What happens on the far side of the moon doesn't matter for us, either,

How do you know? Maybe the far side of the moon is chock-full of exploitable resources. You can't know until you look.

> but we still looked.

Sure, because we could. We cannot look beyond our light cone.

Re: Proving our universe is one among many would be a fourth Copernican revolution

#12

Post by analog31 »

empath75 wrote: post #8
lisper wrote: post #7

> We can only see a finite volume—a finite number of galaxies. That’s essentially because there’s a horizon, a shell around us, delineating the greatest distance from which light can reach us. But that shell has no more physical significance than the circle that delineates your horizon if you’re in the middle of the ocean. No, that's not true. You can rise above the surface of the ocean. Barring some major unforeseen…

it only has physical significance from our perspective.

Ah, but if someone on a distant planet were to record their perspective, e.g., data about their visible universe, and transmit it to us, it would be consistent with our perspective by the time it reaches us. For instance, stars that they can see but we can't, would become visible to us as their message reached us.

Re: Proving our universe is one among many would be a fourth Copernican revolution

#13

Post by tabtab »

analog31 wrote: post #12
empath75 wrote: post #8

Earlier quoted context omitted.

it only has physical significance from our perspective.

Ah, but if someone on a distant planet were to record their perspective, e.g., data about their visible universe, and transmit it to us, it would be consistent with our perspective by the time it reaches us. For instance, stars that they can see but we can't, would become visible to us as their message reached us.

They couldn't transmit such a message; the part beyond "the wall" is moving away faster than light: the data would never reach us. From our perspective, their earlier era is "frozen" in time: red-shifted to zero. We cannot receive any "new" signal from them. Therefore, the seeming "faster than light" violation is not really the case. Relativity "fixes" it by mucking around with time.

From a practical perspective, the red-shift horizon is a pretty solid "wall". The Orange Dude would love it. There could be a million Darth Vaders or run-away planet-eating nanobots on the other side, and they can never touch us. Maybe that's a good thing. The Egyption Empire lasted an extra long time largely because it was so hard to invade. It might even be the Anthropic Principle "protecting" us from really dangerous things.

Re: Proving our universe is one among many would be a fourth Copernican revolution

#14

Post by Phrodo_00 »

lucas_membrane wrote: post #5

> if the universe stretches far enough, everything could happen The article says this. Is this an assertion that the number of things that could happen is finite, or is it an assertion that the number of elements in one infinite set is greater than or equal to the number in another infinite set? Which infinity is equal to the number of things that could happen? How many dimensions would the universe need so that the…

It's also not such an easy assertion to make, distribution of things that could happen matters, and there could be events with 0% probability.

Re: Proving our universe is one among many would be a fourth Copernican revolution

#15

Post by Retric »

lisper wrote: post #11
empath75 wrote: post #10

Earlier quoted context omitted.

What happens on the far side of the moon doesn't matter for us, either, but we still looked.

> What happens on the far side of the moon doesn't matter for us, either, How do you know? Maybe the far side of the moon is chock-full of exploitable resources. You can't know until you look. > but we still looked. Sure, because we could. We cannot look beyond our light cone.

For now we can just by waiting. With every second we see just a little further.

Tomorrow we might look out at the stars and see the tips of giant teeth. But, probably not.

Re: Proving our universe is one among many would be a fourth Copernican revolution

#16

Post by lisper »

Retric wrote: post #15
lisper wrote: post #11

Earlier quoted context omitted.

> What happens on the far side of the moon doesn't matter for us, either, How do you know? Maybe the far side of the moon is chock-full of exploitable resources. You can't know until you look. > but we still looked. Sure, because we could. We cannot look beyond our light cone.

For now we can just by waiting. With every second we see just a little further. Tomorrow we might look out at the stars and see the tips of giant teeth. But, probably not.

You don't quite understand the concept of a light cone.

Yes, we get new data all the time, and the extent of our horizon is growing. But it is always finite. You cannot look backwards past the big bang singularity, and you cannot look forwards beyond "now" for any value of "now".

Re: Proving our universe is one among many would be a fourth Copernican revolution

#17

Post by roywiggins »

analog31 wrote: post #12
empath75 wrote: post #8

Earlier quoted context omitted.

it only has physical significance from our perspective.

Ah, but if someone on a distant planet were to record their perspective, e.g., data about their visible universe, and transmit it to us, it would be consistent with our perspective by the time it reaches us. For instance, stars that they can see but we can't, would become visible to us as their message reached us.

Any information that gets to us via some alien friends will have to travel even further than photons from those stars. By the time we got the alien signal, we would have seen photons from those stars already.

Re: Proving our universe is one among many would be a fourth Copernican revolution

#18

Post by btilly »

lisper wrote: post #7

> We can only see a finite volume—a finite number of galaxies. That’s essentially because there’s a horizon, a shell around us, delineating the greatest distance from which light can reach us. But that shell has no more physical significance than the circle that delineates your horizon if you’re in the middle of the ocean. No, that's not true. You can rise above the surface of the ocean. Barring some major unforeseen…

According to current cosmological thought, the laws of physics at that shell are very close to if not identical to the laws of physics here. And yet, that shell is retreating from us faster than the speed of light. The shell is ever expanding, but we shall never see what that current shell will look like when it is 10 billion years.

How can that be, you ask? It is quite simple. The speed of light is a limit on how fast light can travel through the universe. But the universe is expanding. Light trying to get to us is like a bug crawling over an expanding balloon. If the balloon is expanding faster than the bug is crawling, it can crawl forever but never reach the point it is trying to crawl to.

So there is a fundamental epistemological limit - we can't actually know that our current models are correct. But within existing theory, the location of "the farthest we can see" is not particularly meaningful physically.

Re: Proving our universe is one among many would be a fourth Copernican revolution

#19

Post by ieo838jdkd »

lisper wrote: post #16
Retric wrote: post #15

Earlier quoted context omitted.

For now we can just by waiting. With every second we see just a little further. Tomorrow we might look out at the stars and see the tips of giant teeth. But, probably not.

You don't quite understand the concept of a light cone. Yes, we get new data all the time, and the extent of our horizon is growing. But it is always finite . You cannot look backwards past the big bang singularity, and you cannot look forwards beyond "now" for any value of "now".

We can’t

But 200 years ago we “didn’t need” relativity and then we did

Asking questions and wondering about the things we don’t know is how we now know about many valuable things that, in the past, didn’t appear to be valuable

Re: Proving our universe is one among many would be a fourth Copernican revolution

#20

Post by irrational »

kurthr wrote: post #4
hprotagonist wrote: post #2

The middle of the article reminded me of Asimov: The last question was asked for the first time, half in jest, on May 21, 2061, at a time when humanity first stepped into the light. The question came about as a result of a five dollar bet over highballs, and it happened this way... http://www.multivax.com/last_question.html

It always interested me that this could be Asimov's (1956) response to Arthur C Clarke's (1953), 9 Billion Names of God, where the stars went out.

Those are both fantastic stories.
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