Can a physics type person explain the light barrier thing to me?
Its said that if you break the light barrier you arrive before you've left so its impossible. But if for example it takes 4.4 years to reach alpha centauri at the speed of light. What if you went a bit faster than light and it took 3.9 years or something. If light isn't instant why is it impossible for the light barrier to be breached?

Im crosseyed thinking about it.
( Peej, Thu 22 Oct 2009, 12:46, 33 replies, latest was 16 years ago)

Yeah you're thinking about it wrong
as you speed up time becomes relativiley slower.
So as you get closer to the speed of light every second for you could be 1 minute, 1 year to someone standing still.
When you reach the speed of light time stops. So even if you're in a space ship travelling at the speed of light you'll never be able to stop it because as soon as you hit that speed you'll never be able to reach for the breaks.
(PsychoChomp, Thu 22 Oct 2009, 12:55, Reply)

That is one of the many mind fucks involved in the therory of relativity
I really think it should be taught at primary school level then maybe people will have some understanding of it by the time they're 30.
(PsychoChomp, Thu 22 Oct 2009, 12:59, Reply)

But if time stops at the speed of light how come light isn't instant?
Arrrrrrrrrrrghhhhhhhhhhhhh :P
( Peej, Thu 22 Oct 2009, 13:16, Reply)

it's instant in it's self
but not for any observer.
(PsychoChomp, Thu 22 Oct 2009, 13:21, Reply)

well to be honest
the only argument I can think of regarding this is the fact the light is the fastest travelling thing discovered so far, so we base our physics around it. Im sure it is possible to do it, but you are looking way way off in the future, until then its conjoiner drives not warp drives i'm afraid
(Halfy By light alone, Thu 22 Oct 2009, 12:58, Reply)

wrong

(PsychoChomp, Thu 22 Oct 2009, 13:00, Reply)

which bit?

(Halfy By light alone, Thu 22 Oct 2009, 13:01, Reply)

The first sentance
there's a number of things we've discovered that travel faster than light. Hawkins Radiation is one. We don't base our physics on the speed of light either, we base it on maths. The speed of light was theoretically determined well before it was actually measured.
(PsychoChomp, Thu 22 Oct 2009, 13:10, Reply)

oh well

(Halfy By light alone, Thu 22 Oct 2009, 13:21, Reply)

Hang on a minute
I've not looked this up, but I thought Hawking Radiation was just one part of a pair produced spontaneously at the event horizon of a black hole. By measuring the spin of this particle, one can deduce the spin of the complementary particle (which is the same but negative), therefore this allows information to cross out from beyond the event horizon and therefore allows for the possibility of black holes evaporating.

There's nothing about the radiation travelling faster than light in that theory.

Correct me if I'm wrong though.
( K2k6 has a proper job these days, Thu 22 Oct 2009, 13:25, Reply)

I think you might be right
I haven't really read much on Hawking Radiation. Does raise an interesting point, though - the complementary spin of a pair of particles is always preserved (or so it is thought), to the point that wherever they end up in the universe, if one is changed then its partner will change to complement that. Which suggests some kind of information might be travelling instantaneously and therefore faster than light.

I think I need to sit down for a bit now...
(LongJohnBaldry, Thu 22 Oct 2009, 13:28, Reply)

Yes
But I think it's not so much that you change the spin of the particle, just measure it. But because the act of measurement then gives the spin a definite value, from that instant the spin of the complementary particle (which as you say, may be on the other side of the universe) is also known. So in that sense it is possible for information to be transmitted* faster than light.

*I say transmitted, but it's arguable whether it's actually possible to do anything with the information other than just know it.

I'm off to sit down too. But only because I've been swimming!
( K2k6 has a proper job these days, Thu 22 Oct 2009, 13:33, Reply)

You're on about quantum entanglement, right?

( jim_bob can herd cats., Thu 22 Oct 2009, 13:41, Reply)

Yup

( K2k6 has a proper job these days, Thu 22 Oct 2009, 13:46, Reply)

I can't be bothered to read all that
but due to the uncertainty principle, particles can leave a black hole. To leave a black hole they must be able to travel faster than light.
The travelling thing is a bit wierd because they don't actually leave they just pop into existance somewhere else but that's a problem with wording.
(PsychoChomp, Thu 22 Oct 2009, 13:43, Reply)

I think
you're making up some of that!
( K2k6 has a proper job these days, Thu 22 Oct 2009, 13:47, Reply)

I'm not
black holes evaporate eventually.
(PsychoChomp, Thu 22 Oct 2009, 13:51, Reply)

Sort of, although
it's not quite that simple.

I need to go and look it up though, as I'm far from expert on quantum physics!
( K2k6 has a proper job these days, Thu 22 Oct 2009, 13:55, Reply)

Not true
They leave a black hole because they're one of a particle antiparticle pair created near the event horizon. Ones goes in and the other goes out so it looks like the black hole is radiating. More so because the one which got away has real energy associated with it whereas the one which fell in has negative energy associated with it. So the net energy change for the black hole is negative.

Nothing to do with things travelling faster that light at all.

(Shippy has a phd in particle physics and hopes he's remembered all that correctly.)
(Shippy likes linebreaks and doesn't care what you think, Thu 22 Oct 2009, 13:55, Reply)

That's more as I remember it
and is a better explanation of what I was trying to say up the page a bit.
( K2k6 has a proper job these days, Thu 22 Oct 2009, 14:09, Reply)

^
I'm in the middle of reading this

It explains stuff like this so even bears with very little brains (like what I am) can understand it. Sort of.
(bagofpinenuts, Thu 22 Oct 2009, 12:59, Reply)

I'm reading a children's book on relativity, lent to me by Noel.
I'm still finding it hard going. *laughs*
( girlinthehole, Thu 22 Oct 2009, 13:06, Reply)

One way of looking at this is in terms of the energy involved
One of the quirks of relativity is that it shows mass and energy to be interchangeable, with the result that, the faster something moves, the more mass it appears to have. When you're accelerating something, the force you have to apply to achieve a given acceleration depends on the mass of the object.

So, as something gets faster, you have to apply progressively more force to it to keep on increasing its velocity; i.e., you have to put progressively more energy into the system. But, of course, as you do that, it becomes heavier, and so on in this continuing circle.

If you plot this on a graph, then you see that it's not a simple, straight-line relationship. As you get closer to the speed of light, the amount of mass/energy in the system appears to tend to infinity. The upshot being that you'd have to put in an infinite amount of energy (or your spaceship/Honda Accord would become infinitely heavy) to reach the speed of light.

Because of this mass/energy interchange, therefore, the only things that we know to be able to travel at the speed of light are photons (i.e., particles* of light) which have no mass.

*_{Well, wave-particle dualities, but that's a different can of worms...}
(LongJohnBaldry, Thu 22 Oct 2009, 13:09, Reply)

I knew it was worth waiting for you to reply
rather than saying the same thing but really badly.
( Vipros. clever got me this far, then tricky got me in, Thu 22 Oct 2009, 13:11, Reply)

You're too kind
It's good to know I'm useful for something...
(LongJohnBaldry, Thu 22 Oct 2009, 13:24, Reply)

Ok then Mr. Smarty pants, explain this
If God doesn't exist, who pops up the next Kleenex?
(The Oscillating Gibbon is eating curried squid, Thu 22 Oct 2009, 13:14, Reply)

I knew you'd come back with something like that
Always the deep ones with you, isn't it?

Oh, and I think the answer is "Ganesh" - isn't he "the maintainer"?
(LongJohnBaldry, Thu 22 Oct 2009, 13:16, Reply)

surely the correct answer
is ym
(bamboozled Can hear you getting fatter, Thu 22 Oct 2009, 13:34, Reply)

According to Einstein's theories of relativity
this is indeed the case.

Before Einstein came along, such laws of kinetics were based on Newtonian dynamics, which were derived from everyday observations. It was impossible to prove them wrong and no-one thought there should be any reason for them to be wrong. But Einstein showed that Newtonian dynamics were only a low energy approximation to the 'correct' theory. At high energies, like particles travelling at close to the speed of light, it all goes out the window.

Now, we've tested relativity pretty thoroughly, and it's always been right so far. But that's not to say that we won't be able to come up with other theories in future, which may or may not be testable, which allow for faster-than-light (FTL) travel.

In fact, some people already have come up with this sort of thing. Google 'tacheon'.
( K2k6 has a proper job these days, Thu 22 Oct 2009, 13:31, Reply)

Ah, yes, I've heard about these tachyon types
Not to discount it, I'm sure it's a perfectly valid theory rather than just a quirk of the maths (after all, that's how we first discovered antimatter) but someone is going to need to come up with a way to test that theory...
(LongJohnBaldry, Thu 22 Oct 2009, 13:33, Reply)

It's even out of the league
of the LHC boys at CERN. I think they'd need to harness the power of a whole star and build an interplanetary accelerator to do that!

And you're right - it's tachyon, not tacheon. My mistake.
( K2k6 has a proper job these days, Thu 22 Oct 2009, 13:35, Reply)

The whole tachyon thing
Is totally allowed in GR, it means that they must always be travelling faster then c just as all us slow-coaches must always travel slower than c.
(Shippy likes linebreaks and doesn't care what you think, Thu 22 Oct 2009, 14:17, Reply)

I took my car to be serviced by a quantum mechanic today.
He says it'll be ready last wednesday.
(Captain Placid 24/7 ball gags, brownie mix and clown porn, Thu 22 Oct 2009, 17:15, Reply)