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The Disappearing Universe
- dave809 12y agoLeonard Susskind talked about this idea and expanded on it in his talk 'Why is time a one way street' Highly recommend the talk. http://www.youtube.com/watch?v=jhnKBKZvb_U http://www.youtube.com/watch?v=jhnKBKZvb_U
- hcarvalhoalves 12y agoThat was very interesting, thanks for sharing. I can see the elegance of using fractal math to explain the big bang, cosmological expansion and the apparent structure our universe exhibits (as opposed to being an inert soup).
- glbrew 12y agoNow I'm sad
- VanillaCafe 12y agoOn the bright side, we'll probably never explore much of our galaxy, let alone the universe at large.
- sigterm 12y agothat just makes it worse...
- platz 12y agoThis might help http://www.thrivenotes.com/the-last-question/ http://www.thrivenotes.com/the-last-question/
- spullara 12y agoI'm pretty convinced we will either die out or fill the galaxy with people. If we can start the reaction by going one other place and inhabiting it I think it will ultimately set off a chain reaction. Lots of work to do between now and then but it seems like its mostly engineering now vs new discoveries.
- hueving 12y ago> Lots of work to do between now and then but it seems like its mostly engineering now vs new discoveries. I'm not sure what you mean by this. There are still lots of issues with just surviving the journey, let alone making a foreign planet habitable and establishing a society. We need lots more discoveries in energy and understanding human physiology before it becomes just an engineering problem.
- sprash 12y agoDon't worry, we will collide with Andromeda before our Sun will die. So at least one other Galaxy can be "explored".
- noselasd 12y agoOr really, any of the about 50 galaxies in our local group. If we could travel at light speed that is, which we can't and likely never will.
- 0xeeeeeeee 12y agoI always get half-sad half-glad when I read these types of things. Glad that I won't have to see this depressing end to the universe but still sad for humanity, that we won't last forever.
- maaku 12y agoI don't know about you but I plan on lasting forever.
- db48x 12y agoBut barring that, I'd settle for a couple thousand years.
- seszett 12y agoSame for me, I hope I am among the 6.5% of humans who don't die[0]! [0] https://en.wikipedia.org/wiki/World_population#Number_of_humans_who_have_ever_lived https://en.wikipedia.org/wiki/World_population#Number_of_hum...
- nerfhammer 12y agoOver the billions of years this will take humanity's descendants will probably figure out how to create whatever universes they want
- twic 12y agoBeyond the reachability limit, there's something even sadder, but possibly even more poetic: the comoving future visibility limit. That's the surface beyond which, although matter may exist, light from it will never reach us. In terms of time, it's very, very early - before the luminous phase of the big bang which gives us the cosmic microwave background. It's the very last thing on the map of the universe: http://www.astro.princeton.edu/universe/ http://www.astro.princeton.edu/universe/
- fhars 12y agoThere is actually a whole sequence of such limits: the visibility limit (where light emitted in the distant past reaches us now) is furthest out, then comes the reachability limit (where light emitted by us now can still be observed), then the round trip limit where we can send a message now and recieve an answer (before we are beyond their reachability limit), then the limit where we can send a message, recieve an answer and then send a final goodbye, then the limit for two full exchanges, and so on... But at least one could do the respective trips to slightly closer galaxies within a lifetime: http://arxiv.org/pdf/astro-ph/0509268.pdf http://arxiv.org/pdf/astro-ph/0509268.pdf (published in Phys.Rev. D, http://journals.aps.org/prd/abstract/10.1103/PhysRevD.72.107302 http://journals.aps.org/prd/abstract/10.1103/PhysRevD.72.107... )
- nkoren 12y agoI first read about this many years ago, in Olav Stapledon's brilliant Star Maker, about a man who takes a magical mystery tour through the whole of time and space: "Then the Star Maker said, "Let there be light." And there was light. From all the coincident and punctual centers of power, light leapt and blazed. The cosmos exploded, actualizing its potentiality of space and time. The centers of power, like fragments of a bursting bomb, were hurled apart. But each one retained in itself, as a memory and a longing, the single spirit of the whole; and each mirrored in itself aspects of all others throughout all the cosmical space and time. "No longer punctual, the cosmos was now a volume of inconceivably dense matter and inconceivably violent radiation, constantly expanding. And it was a sleeping and infi-nitely dissociated spirit.But to say that the cosmos was expanding is equally to say that its members were contracting. The ultimate centers of power, each at first coincident with the punctual cosmos, themselves generated the cosmical space by their disengagement from each other. The expansion of the whole cosmos was but the shrinkage of all its physical units and of the wave-lengths of its light. Though the cosmos was ever of finite bulk, in relation to its minutiae of light-waves, it was boundless and center-less. As the surface of a swelling sphere lacks boundary and center, so the swelling volume of the cosmos was boundless and center-less. But as the spherical surface is centered on a point foreign to it, in a "third dimension," so the volume of the cosmos was centered in a point foreign to it, in a "fourth dimension." "The congested and exploding cloud of fire swelled till it was of a planet's size, a star's size, the size of a whole galaxy, and of ten million galaxies. And in swelling it became more tenuous, less brilliant, less turbulent. Presently the cosmical cloud was disrupted by the stress of its expansion in conflict with the mutual clinging of its parts, disrupted into many million cloudlets, the swarm of the great nebulae. "For a while these were as close to one another in relation to their bulk as the flocculations of a mottled sky. But the channels between them widened, till they were separated as flowers on a bush, as bees in a flying swarm, as birds migrating, as ships on the sea. More and more rapidly they retreated from one another; and at the same time each cloud contracted, becoming first a ball of down and then a spinning lens and then a featured whirl of star- streams. "Still the cosmos expanded, till the galaxies that were most remote from one another were flying apart so swiftly that the creeping light of the cosmos could no longer bridge the gulf between them." Written, impossibly, in 1936.
- Gobiel 12y agoIf we could achieve near-light speed, how would time work for those traveling at that speed relative to the universe ? Wouldn't time "feel" normal but "stopped" relative to the other slower bodies of the universe ? As such, couldn't that near-light speed "slow down" the rate at wich we see the expansion of the universe, making possible star traveling ?
- Udo 12y agoBeing aboard a spaceship that's accelerated to such speeds would feel pretty normal internally, but the outside universe would pass by very quickly and processes in that universe would appear to be impossibly fast. Accelerated to a very significant fraction of c would allow you to visit practically everywhere in the galaxy within a few years of ship time. But on the outside, millennia will have passed. You can see why that's not practical, because everything you left behind would be gone. Still, there are scenarios where this might be a valid solution. However, you could never reach a destination that's speeding away from you faster than the speed of light. Because you can't accelerate your spacecraft beyond that speed, parts of the universe will always be unreachable - which is the point of the article. You might wonder why galaxies moving away from each other faster than the speed of light works at all given the cosmic speed limit. The answer is that their "movement" is not normal, inertial movement as we know it. Instead you might imagine that new space is being created in between them, driving them away from each other by simply scaling up the distances involved. Given the practical and theoretical limits on spacecraft acceleration, people have been thinking about a different way to travel, a way that doesn't involve momentum but instead manipulates spacetime to simply shift an object to another position without acceleration. The article hints at this as well. It makes sense because technically the acceleration and deceleration part of a journey is wasteful and limiting. At this time, it's the only way we know how to get from A to B, but we're all hopeful that one or more alternatives can be researched which allow us to simply go somewhere else without using traditional movement.
- ivanca 12y agoI'm looking at the bright side, it means that we don't even need to achieve speed of light to travel to other galaxies, because the universe is ever-expanding it means that some planets will occupy the space our planet is in now, so theoretically if we can figure how to live in a static point in the universe (e.g, absolute position, not relative to our solar system) some day in the future (millions of years from now) we could visit other galaxies.
- maaku 12y agowhat? No. there is absolutely no such thing as an absolute position in the universe.
- edem 12y agoWhat if we find the point where the Big Bang happened?
- stevensanderson 12y agoThat's exactly where you are right now (and everywhere else).
- bkeroack 12y agoThis illustrates the confusion that occurs when people are exposed to horrible "artistic renderings" of the Big Bang as a huge explosion that throws matter all over the place. It's better to think of the Big Bang as an unimaginably intense period of expansion and cooling of whatever substance the earliest universe was made out of (see Inflation theory). It was not an explosion that happened in a pre-existing spacetime.
- jloughry 12y agoWhat if we find the point where the Big Bang happened? You're already there. Since all of space expanded from one point, by definition the Big Bang actually happened right here (and also over there) [1]. [1] http://en.wikipedia.org/wiki/Brouwer_fixed-point_theorem http://en.wikipedia.org/wiki/Brouwer_fixed-point_theorem
- dkural 12y agoIt is very interesting that essentially there are causally disconnected subsets of the universe - each a sub universe onto their own. Although globally not possible, is the gravitational collapse scenario plausible for some of these causally disconnected subsets? Tying it with the fact that galaxies seem to be slowly eaten by their black hole centers, would this be an example of a local gravitational collapse? And when this process is over, what happens to all the black holes, isolated from everything else.. do they just dissipate out, creating a uniform, cold, low entropy universe?
- bkeroack 12y agoIt would be a uniform, cold, high entropy universe. The highest entropy possible. Once all the black holes had eaten through all matter and subsequently all radiated away (via Hawking radiation).
- bronson 12y agoCorrect. As we understand it now, the black holes will slowly evaporate through Hawking radiation. http://en.wikipedia.org/wiki/Future_of_an_expanding_universe#Black_Hole_Era http://en.wikipedia.org/wiki/Future_of_an_expanding_universe... And, after that, oblivion. http://en.wikipedia.org/wiki/Heat_death_of_the_universe#Current_status http://en.wikipedia.org/wiki/Heat_death_of_the_universe#Curr...
- emeraldd 12y agoI wonder if this has any impact on the Fermi Paradox? Could it be that any sufficiently advanced civilization finds itself beyond the "red out" horizon before having a chance to say hello to anyone else? (Pure speculation of course, but so is the question in the first place.)
- lisper 12y agoAlmost certainly not. You don't need to leave our galaxy to make the case for Fermi's paradox. Something more like a Great Filter (http://en.wikipedia.org/wiki/Great_Filter http://en.wikipedia.org/wiki/Great_Filter) is more likely in play.
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- p1mrx 12y agoIf there's any possible way to corrupt spacetime, resulting in a sphere of destruction that expands outward at the speed of light, then maybe an accelerating universe could act as a firewall. What if we're here because the non-accelerating universes with intelligent life tend to get wiped out?
- fish2000 12y ago> corrupt spacetime Like (say) a vacuum metastability event? http://en.wikipedia.org/wiki/False_vacuum#Vacuum_metastability_event http://en.wikipedia.org/wiki/False_vacuum#Vacuum_metastabili...
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- dtbx 12y agoThere is a novel about that. "Schild's Ladder", by Greg Egan. But in that novel, the sphere of destruction expands only at c/2.
- stcredzero 12y agoIf it expanded at C, it would be a shorter book.
- jofo25 12y agoI seem to remember from physics class that mass cannot travel faster than the speed of light, so how is it possible for galaxies to be unreachable if you managed to travel at the speed of light?
- gerhardi 12y agoImagine that you go running with a friend. You run at 0.9 * speed of light and your friend runs at 0.8 * speed of light in the exact opposite direction. How fast are you getting away from each other?
- epi16 12y agoI'm not sure I understand. It seems like you're implying that the two people would be moving away from each other faster than the speed of light, but I was under the impression that that's not the case. I thought that each person would observe the other travelling at C?
- VexXtreme 12y agoI think they would observe each other traveling at C but would experience visible time dilation (in the other person's frame of reference).
- danbruc 12y ago1.7c for an observer just standing around and watching the two guys run. I am not sure what it looks like from the point of view of the runners without calculating it but they should see a speed smaller than the speed of light.
- vidarh 12y agoIt is possible because the galaxies are not travelling faster than light. Space is expanding. Consider if you were travelling on the surface of an expanding balloon. Your distance from the starting point would increase faster than your speed relative to the surface at your current spot, because the part of the surface you'd already travelled across would continue expanding. Now do that in three dimensions.
- 2Pacalypse- 12y agoLawrence Krauss talked about this in his entertaining and famous talk, A Universe From Nothing[1]. [1] - http://www.youtube.com/watch?v=7ImvlS8PLIo http://www.youtube.com/watch?v=7ImvlS8PLIo