Is this FTL?

[5614]

(FTL = faster than light)

 

OK, I know you may automatically respond "it's impossible" and I know it is, but explain this:

 

You have a disk rotating at 0.25C (powered by a motor), then attached to the center of that rotating disk you have another motor turning another disc at 0.25C and then a 3rd and a 4th etc...

 

So all relative to me (at rest), unless specified:

Motor1 body is stationary,

motor1 moving head rotating at 0.25C,

motor2 main body is rotating at 0.25C (attached to disk1 which is attached to the moving head of motor1)

and then the moving head of motor2 is rotating at 0.25C relative to the main body of the motor2,

making disk2 (attached to motor2) move at 0.5C

because motor2 is rotating at 0.25C and then the rotating head of it is moving at 0.25C as well, giving a combined speed of 0.5C

(I might have got the maths wrong, but it'd be moving faster than 0.25C, there'd be a speed gain)

 

In the end, if you were standing by watching all of this, surely the end disk would be rotating at more than C.

 

OK, so you may not be able to get a disk to spin at 0.25C so you get it to spin at 0.0001C and you need over a thousand discs, it's still practical.

 

Is that clear what I mean? It is to me, but then I kinda have this image in my head, I could put it into paint if you really don't get it.

(Imagine a helicopter with rotating blades moving at 0.25C... but the whole helicopter is on a rotating stand so the blades move faster 0.25C, compared to if the whole helicopter was stationary)

[Janus]

By "rotating at .25c" I'm goin to assume that you mean that the outer edge of the disk is moving a .25c.

 

This is simply another example of the Relativistic addition of velocities, namely that velocities do not add by the relationship of

[math]w=u+v[/math]

 

but by

[math]w=\frac{u+v}{1+\frac{uv}{c^2}}[/math]

 

In this case, your second disk would rotate at

 

[math]\frac{.25c+.25c}{1+\frac{(.25c)(.25c)}{c^2}} = .4c[/math]

 

relative to you.

 

Meaning that if the second disk was rotating at .25c relative to the first disk as measured from the first disk, then relative to you, it would move at .4c.

 

if I add a third disk moving at .25c relative to the second it would be moving at

 

[math]\frac{.25c+.4c}{1+\frac{(.25c)(.4c)}{c^2}} = .559c[/math]

 

forth disk:

[math]\frac{.25c+.559c}{1+\frac{(.25c)(.559c)}{c^2}} = .778c[/math]

 

fifth disk:

[math]\frac{.25c+.778c}{1+\frac{(.25c)(.778c)}{c^2}} = .988c[/math]

 

sixth disk:

[math]\frac{.25c+..988}{1+\frac{(.25c)(.988)}{c^2}} = .993c[/math]

 

seventh disk:

 

[math]\frac{.25c+.993c}{1+\frac{(.25c)(.993c)}{c^2}} = .996c[/math]

 

eighth disk

 

[math]\frac{.25c+.995}{1+\frac{(.25c)(.995c)}{c^2}} = .997c[/math]

 

ninth disk

 

[math]\frac{.25c+.997c}{1+\frac{(.25c)(.997c)}{c^2}} = .998c[/math]

 

tenth disk

 

[math]\frac{.25c+.998c}{1+\frac{(.25c)(.998c)}{c^2}} = .999c[/math]

 

eleventh disk

 

[math]\frac{.25c+.999c}{1+\frac{(.25c)(.999c)}{c^2}} = .9994c[/math]

 

twelveth disk

 

[math]\frac{.25c+.9994c}{1+\frac{(.25c)(.9994c)}{c^2}} = .9996c[/math]

 

notice that each successive disk's velocity increases by a smaller and smaller amount.

No matter how many disks you add the last disk will always move at less that c relative to you.

 

If on the other hand you try to arrange it that each disks velocity increases by .25c as measured by you, then each disk will have to rotate faster with respect tot he last disk as measured by that disk.

 

for instance if you want the second disk to rotate at .5c as measured by you then the second disk woud have to rotate at .286c realtive to the first disk as measured from the first disk.

 

The third disk would have to rotate at .4c relative to the second in order for it rotate at .75 c as measured by you.

 

And the fourth disk would have to rotate at 1c relative to the third to reach 1c as measured by you. But since the third disk cannot rotate at 1c relative to the third, this can never happen.

 

In short, the only way for the last disk to have a velocity greater than c relative to you is that at least one of the disks to have a greater than c velocity relative to the disk it rests on.

 

It doesn't matter is each disk rotates at .001c or .25c relative to the one before, the answer comes up the same; you can't acheive FTL speeds this way.

[5614]

Oh, ok, so basically no matter how many disks you had you'd never reach C, that sounds a bit better than my theory!!!

 

Thanks,

 

Just outta interest though as you showed you'd be getting quite close to C... with enough disks you'd have like 0.99999999999C and if you had enough disks I suppose it comes down to 'how big is infinite' you'd have like 10,000 million billion 9s in a row and it still wouldn't be precisely C, I suppose if you had an infinite amount of disks you'd have an infinite amount of 9s and 0.9recurring is 1, but you can't have infinite amount of disks so that solves that!

 

thanks again.

[alt_f13]

What would happen if you were on a spaceship going .999999999[etc]c and you tried to move your hand foreward?

 

To someone outside, time would just slow down too much for my hand to reach c right?

 

 

Is that what that equation accounts for?

[5614]

Yeah, you can always add another 9 to the end of that row of 9s!

 

I suppose it comes down to 'how big is infinite' you'd have like 10,000 million billion 9s in a row and it still wouldn't be precisely C, I suppose if you had an infinite amount of disks you'd have an infinite amount of 9s and 0.9recurring is 1, [b']but you can't have infinite amount of disks so that solves that![/b]

[J.C.MacSwell]

What would happen if you were on a spaceship going .999999999[etc]c and you tried to move your hand foreward?

 

To someone outside' date=' time would just slow down too much for my hand to reach c right?

 

 

Is that what that equation accounts for?[/quote']

 

If I (from my inertia frame) watch you do this my time does not slow down. Your time (from my perspective) would stay the same (almost, it would actually speed up as you lost momentum to your hand/arm), but your "hand's time" would slow down further. Only temporary (no pun intended) of course until your hand resumed the velocity of your body but from my perspective that could be a long time.

[psicicle]

hmmm, what about if you had a giant disk and spun it, would it be possible to make the disk big enough so the outsides are travelling faster than the speed of light? My guess is that the disk would never balance out to finite size and finite energy to spin it but I don't really know.

[swansont]

hmmm, what about if you had a giant disk and spun it, would it be possible to make the disk big enough so the outsides are travelling faster than the speed of light? My guess is that the disk would never balance out to finite size and finite energy to spin it but I don't really know.

 

No. No part of the disk is going to be able to go faster than c.

 

One of the repercussions of SR is that there can be no infinitely rigid materials, which is why the "if I push on an infinitely rigid rod, doesn't the other end move instantly and violate causality" argument fails. So the disk necessarily flies apart.

[Crusty_Ass]

Exactly, strenght of matter is finite.

[Dak]

what about the plane of light? i heard that if you change the plane of one end of a beam of light, then the other end of the beam changes plane instantaniously?

 

oh, and just out of sheer curiosity, any specific reason for your name, crusty ass? jus wonderin.

[swansont]

what about the plane of light? i heard that if you change the plane of one end of a beam of light' date=' then the other end of the beam changes plane instantaniously?

[/quote']

 

It sounds like you might be thinking of entangled photons. It doesn't work that way. There have been many threads on this - use the search function.

[Dak]

i looked up a few threads on entangled photons. ill tell you now that im by no means even approaching demi-adept at even basic quantum phisics, but i dont believe photonic entanglement was what i was thinking of, though it may be related.

 

i remember hearing of an experiment where a beam of light was beamed to a recepter through a filter, which meant that the light being beamed was in the horisontal plane.

 

when the filter was rotated, so that the plane of the light being emited was also rotated, the rotation was detected at the recepter instantaniously - ie, the rotation of the beam of light was transmited from one end of the beam of light to the other at a speed faster than c.

 

like the stick thingy, but without the problem of no matter being infinitely ridgid, i suppose.

[J.C.MacSwell]

i looked up a few threads on entangled photons. ill tell you now that im by no means even approaching demi-adept at even basic quantum phisics' date=' but i dont believe photonic entanglement was what i was thinking of, though it may be related.

 

i remember hearing of an experiment where a beam of light was beamed to a recepter through a filter, which meant that the light being beamed was in the horisontal plane.

 

when the filter was rotated, so that the plane of the light being emited was also rotated, the rotation was detected at the recepter instantaniously - ie, the rotation of the beam of light was transmited from one end of the beam of light to the other at a speed faster than c.

 

like the stick thingy, but without the problem of no matter being infinitely ridgid, i suppose.[/quote']

 

Some kind of delayed choice thing?

[swansont]

i looked up a few threads on entangled photons. ill tell you now that im by no means even approaching demi-adept at even basic quantum phisics' date=' but i dont believe photonic entanglement was what i was thinking of, though it may be related.

 

i remember hearing of an experiment where a beam of light was beamed to a recepter through a filter, which meant that the light being beamed was in the horisontal plane.

 

when the filter was rotated, so that the plane of the light being emited was also rotated, the rotation was detected at the recepter instantaniously - ie, the rotation of the beam of light was transmited from one end of the beam of light to the other at a speed faster than c.

 

like the stick thingy, but without the problem of no matter being infinitely ridgid, i suppose.[/quote']

 

Do you have a citation for it? It does sound like an entanglement experiment.

[Dak]

i had a look on pubmed and google and couldnt find it, sorry. when i heard about it, it had just been published so its possible that it didnt survive the peer review prosess.

[Ollie]

Dredging from my memory, could this be the "Twisted Light" article that New Scientist ran a while ago? Not sure at all though.