Paul asks…
If aliens bent space-time around us, would we notice it?
It’s talked about a lot in science fiction. The fastest way to get from one point in the universe to another distant point would theoretically be to warp space and time some how to create a worm hole. Some movies have space ships that are powerful enough to do such a thing and allow instant teleportation. I still have trouble wrapping my head around how space-time can be curved or pierced probably because I can’t picture what curved space would look like. If the region of space-time we were living in was being curved by some advanced alien using such a theoretical technology, would we notice anything different around us?
Also is space-time layered? I’ve often seen it represented as a wireframe sheet of paper, with a large object causing a dip in the sheet of paper, or a black hole causing a funnel. However, is the real space-time a sheet? Is it many sheets? Or is it continuous and unbroken in all directions? Because if it’s the latter, I can’t see a sheet representation being very helpful as a visual aid. What would the curvature of space-time look like in a model if you weren’t showing just a sheet or cross section of it?
Larry, what is if they bent the very region of space time we were actually inhabiting (i.e. a region that includes the earth). Would the earth become misshapen, or would it look the same to us?
Joy answers:
We can currently see the effects of space time curvature by observing gravitational lensing of distant galaxies. What we see is a substantial gravity well – like a cluster of massive galaxies – with distorted images of even more distant galaxies surrounding it. The closer galaxy cluster is bending and distorting light from the more distant galaxies as it passes on its way to us. So we can see such evidence today, and it is well understood (ref. Einstein’s Telescope by Dr. Evalyn Gates). If advanced civilizations were actively and continuously bending space time, we would be able to detect it, but only if they were doing it within the light cone that we can see. For example, if they were doing it within the Andromeda Galaxy, we could only see it if they were acting more than 2 million years ago in our time reference. If they did it, for example – 1 million years ago, then the light from the distorted image would not have reached us yet.
As far as the rubber sheet analogy, I find that to be a pretty inadequate representation of the way that gravity really works. If you think about it, the analogy uses gravity to explain gravity. The only thing that distorts the rubber sheet with a ball on it is gravity. So it’s a circular argument. Einstein never called space time a “fabric,” and it is decidedly not a fabric. Understanding the curvature of space time is not very intuitive. It takes some imagination, and familiarity with mathematics helps, but it is still not very clear in a visual sense, although it appears to be precisely accurate.
ADDED: The layered image is probably another inadequate analogy of the parallel universe idea – another time-saving mathematical device that sort of leaves me cold in terms of actual physical reality. I would not spend too much time on it, since it doesn’t make much sense unless you are trying to avoid the difficult math involved in quantum mechanics.
ADDED (2): I have to believe that if it looks different to them – i.e. By creating a short cut to get around us – it would look different to us as well. We would be able to see something other than the near-perfect continuum in all directions that we are currently observing. There is no reason to believe that anything like this is in fact occurring, based on what we can see.
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