h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Hey, saw this mentioned in the talking point. Is light speed travel possible? Would time really slow down? Where's the proof? Are there any theoretical alternatives to light speed travel? Faster than light?

It's not possible to travel at light speed, but it is possible theoretically to travel at slightly less than light speed. Time does indeed slow down for you, but not for anybody else. This has been verified on a small scale by sending accurate clocks in fast space rockets around the earth. The clock that travels at speed is behind the one which stays on the earth.

You can't go faster than light since you can never reach light speed.

Why does it slow down? I don't understand. Are light and time related?

Speed and time are related.

Ok, how? Or do we not know yet? Theories?

Sorry, this one has been bending my brain for years.

Try this guide entry,

http://www.bbc.co.uk/dna/h2g2/alabaster/A535574

Thank you, Seth, that link gave me a handle on something I've been accepting but unable to grasp.

Meanwhile, as an aside: When the London Planetarium was newish, I visited & stayed on for questions to the lecturer, one of which was, of course, star travel... "simply" said he, "impossible". OK & so it still seems - at least as a practical project. However, since that question, I've had that disquieting suspicion that if it actually STAYS impossible then our species (with its questing mind but a brick wall getting ever nearer) is already dead - or as good as.
We carry within us the seeds of our own detrucion?

Well if the universe implodes then our species is dead. Not something to worry yourself about. It seems likely that Relativity will be replaced as a theory at some point before interstellar space travel becomes a real concern, but I rather suspect that the speed-of-light limitation may hold. It has a certain elegance about it.

Tachyons are particles supposedly created travelling faster than light speed, but there is no actual evidence for them, they're just a theoretical possibility if you allow imaginary* solutions of Relativity. In any case, if they did exist then they're probably not much help to us - you still need infinite energy to accelerate through the speed barrier.

*Imaginary numbers are multiples of the square root of -1.

if space has multiple, higher dimensions, and space is severely warped in these dimensions, then it seems you could maybe find a short cut from point A to B in our space by travelling through the higher dimensions - effectively exceeding the speed of light if just viewed in our 3D, but never actually exceeding the speed of light.

I believe they are planning that extra-dimensions theory sometime. Something about firing a special type of neutrino that can flip into the extra dimensions (I believe they are called the 'bulk' or something) from one point to another on the earth's surface and having it arrive before it leaves.

>> I've had that disquieting suspicion that if it actually STAYS impossible then our species (with its questing mind but a brick wall getting ever nearer) is already dead - or as good as. <<

... hopefully not in our lifetimes

Mere disquiet is quite refreshing really, especially about things I know I can't affect...

Surely, taking shortcuts through other dimensions/universes is cheating? Don't we really want bigger & better engines? Even if they are heavier.

I seem to remember reading about fairly early on in the bIG bANG, when our universe was pretty small but expanding faster than light speed? If that hasn't been discredited already, then there are circumstances in which...

Space can expand faster than light, so that two points which are a certain distance apart can be further apart later on as if one of them had travelled faster than light. But within space, we can't travel faster than light.

Ah, yes Gnomon, that prompted a memory of a nice analogy from some time back.

You may find the short article here of interest. It's still just a theory for now but who knows what the future might bring?

http://www.astro.cf.ac.uk/groups/relativity/papers/abstracts/miguel94a.html

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String theory postulates extra dimensions, but IIRC these are "unexpanded" and couldn't serve to get from one point of normal space to another. The apparent extra dimensionality of normal space (that enables the universe to be finite and unbounded) is a function of the curvature of the three standard dimensions, so there are still no shortcuts. This is still provisional though. As always in science, new data could lead to a change in our understanding.

Noggin

Absolutely, but I was referring to work by Lisa Randall which involved highly warped, non-compact extra dimensions (and does not require string theory).

I'm not familiar with this. Can you expand?

How non-compact is non-compact? Wouldn't extra expanded dimensions have a more direct effect on the three we know about?

Noggin

And as an afterthought, could this be used to explain "spooky action at a distance"?

Noggin

I wish I could explain it, or find a good link, but I can't. There's an interview with Lisa Randall (by Charlie Rose):
http://video.google.com/videoplay?docid=-45154219728824809&sourceid=searchfeed%20

Basically, an idea is that electromagetism, the weak and the strong forces are confined to our local, 4D world. These forces are much much stronger than gravity. When we measure things in our $D we're mainly using the electromagnetic force. So since EM is confined to our 4D, that's all we really see.

One of the big puzzles of physics is why is gravity so much weaker than the other 3 forces. I think LR's answer says that while EM, the strong and the weak are confined, gravity is not confined, and her part is to say that gravity is mainly confined to another 4D region that is separated from our 4D region along the 5th dimension.