Physicists: My theory of obtaining lightspeed!

themistry · 26 Oct 2006 at 14:51

Visage said:
You've got the right reasoning, but the wrong conclusion.

For example, you could apply the same logic to a space shuttle launch - namely that the force on the earth will push it backwards just as much as it pushes the shuttles forwards (or upwards, more precisely). The difference is, obviously, the different masses involved.

Isn't it also todo with the enrgy involved? I.e. the force exerted to reach such speeds would be enough to displace the moon or any other body for that matter?

TM

Visage · 26 Oct 2006 at 14:56

themistry said:
Isn't it also todo with the enrgy involved? I.e. the force exerted to reach such speeds would be enough to displace the moon or any other body for that matter?

TM

Energy does come into it, but its mainly due to forces. Its like using a pea shooter - the (lightweight) pea goes at very high speed, wheras you dont feel any recoil in your (heavier) body.

SteveOBHave · 26 Oct 2006 at 14:59

Visage said:
Energy does come into it, but its mainly due to forces. Its like using a pea shooter - the (lightweight) pea goes at very high speed, wheras you dont feel any recoil in your (heavier) body.

Therein lies the problem. The forces we're talking about are massive, whilst there is a pea and a shooter, the actual force behind the acceleration is simply astronomical.

themistry · 26 Oct 2006 at 14:59

Visage said:
Energy does come into it, but its mainly due to forces. Its like using a pea shooter - the (lightweight) pea goes at very high speed, wheras you dont feel any recoil in your (heavier) body.

but if you expelled the pea with enough force to accelerate it to light speed, surely you would feel it. A bullet barely breaks the sound barrier... yet the recoil from a hand gun is very measurable... i think a bullet launched at light speed would have a considerable amount of backwards force?

TM

themistry · 26 Oct 2006 at 15:00

SteveOBHave said:
Therein lies the problem. The forces we're talking about are massive, whilst there is a pea and a shooter, the actual force behind the acceleration is simply astronomical.

Agreed,

TM

Visage · 26 Oct 2006 at 15:09

themistry said:
but if you expelled the pea with enough force to accelerate it to light speed, surely you would feel it. A bullet barely breaks the sound barrier... yet the recoil from a hand gun is very measurable... i think a bullet launched at light speed would have a considerable amount of backwards force?

TM

Undoubtedly. But the OP's scheme has much deeper flaws than that

daz · 26 Oct 2006 at 15:10

themistry said:
but if you expelled the pea with enough force to accelerate it to light speed, surely you would feel it. A bullet barely breaks the sound barrier... yet the recoil from a hand gun is very measurable... i think a bullet launched at light speed would have a considerable amount of backwards force?

TM

That's because bullets have a non-trivial mass, and bigger guns firing bigger bullets have even bigger recoil.

Visage · 26 Oct 2006 at 15:17

Ive just done a back-of-an-envelope calculation.

If one were to power a 1 metric tonne car with a 'photon drive', then assuming the drive was 100% efficient, and you wanted to be able to do 0-60 in 10 seconds, you would need a 900 Gigawatt power supply.

locutus12 · 26 Oct 2006 at 15:29

Minto said:
You didn't link to any article about that, you could have just made it up.

http://www.phys.unsw.edu.au/einsteinlight/jw/module6_constant.htm

and dont be such an insulting bugger in future.

Alan! · 26 Oct 2006 at 15:33

Visage said:
Ive just done a back-of-an-envelope calculation.

If one were to power a 1 metric tonne car with a 'photon drive', then assuming the drive was 100% efficient, and you wanted to be able to do 0-60 in 10 seconds, you would need a 900 Gigawatt power supply.

That sounds crazy. A 900Gigawatt photon drive would get beat by a 1200cc petrol engine?

daz · 26 Oct 2006 at 15:39

Locutus, of course the speed of light changes when travelling through a medium (well, the photons are absorbed and then re-emitted by the atoms). Relativity uses the speed of light in free space (in a vacuum).

Visage · 26 Oct 2006 at 15:45

Alan! said:
That sounds crazy. A 900Gigawatt photon drive would get beat by a 1200cc petrol engine?

In these circumstances, yes.

Shoseki · 26 Oct 2006 at 15:47

SteveOBHave said:
oh - I Googled it and looked it up on Wiki and both came up with International Mountain Bicycling Association LOL

And thus wikipedia is edited

DaveF · 26 Oct 2006 at 15:58

Alan! said:
That sounds crazy. A 900Gigawatt photon drive would get beat by a 1200cc petrol engine?

Point is, a photon drive ain't efficient - most of the energy is 'wasted' in the form of a hugely powerful photon exhaust.

P.S. Best not to stand behind the car...

Psyk · 26 Oct 2006 at 16:00

Visage said:
You've got the right reasoning, but the wrong conclusion.

For example, you could apply the same logic to a space shuttle launch - namely that the force on the earth will push it backwards just as much as it pushes the shuttles forwards (or upwards, more precisely). The difference is, obviously, the different masses involved.

Not to mention the fact that the stationary mass in eXSBass's idea is completely pointless. You do not need anything to push off with unless you're poking it with something solid. Once the photons/ions/water molecules have left your ship, there's no way for them to transfer more energy back to it. Try firing a powerful hose first into the air, and then into a wall. You'll find it makes no difference to the recoil.

SteveOBHave · 26 Oct 2006 at 16:13

Shoseki said:
And thus wikipedia is edited

LOL are you supposed to do it that way? I thought you were supposed to create a new entry, not radomly edit someone elses

callmeBadger · 26 Oct 2006 at 16:32

Alan! said:
That sounds crazy. A 900Gigawatt photon drive would get beat by a 1200cc petrol engine?

but the 1.2l engine would max out at around 100 - 120 mph on the ground, whereas the photon drive would keep accelerating and beable to reach speeds somewhere around 10% that of light speed.

And as its not burning fossil fuels, just blinding anyone foolish enough to look at it, you wouldn't have to pay congestion charging nipping into town to buy a pint of milk.

Psyk · 26 Oct 2006 at 16:44

SteveOBHave said:
LOL are you supposed to do it that way? I thought you were supposed to create a new entry, not radomly edit someone elses

Really he should have made a separate article and made a disambiguation page, rather than just tacking on the end of an article about something else.

locutus12 · 26 Oct 2006 at 16:45

daz said:
Locutus, of course the speed of light changes when travelling through a medium (well, the photons are absorbed and then re-emitted by the atoms). Relativity uses the speed of light in free space (in a vacuum).

the first link i posted isnt quite what i thought it was... the second links more interesting

themistry · 26 Oct 2006 at 17:04

daz said:
That's because bullets have a non-trivial mass, and bigger guns firing bigger bullets have even bigger recoil.

Isn;t this the point I was making? :confused:

TM