Beat the speed of light


by henrywang
Tags: beat, light, speed, speed of light
henrywang
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#1
Feb18-14, 12:07 PM
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If a a object is falling in a gravity field with infinitly long radius. can it eventually travel faster than the speed of light?
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phinds
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#2
Feb18-14, 12:52 PM
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Quote Quote by henrywang View Post
If a a object is falling in a gravity field with infinitly long radius. can it eventually travel faster than the speed of light?
No. Nothing travels faster than c. Period.
henrywang
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#3
Feb18-14, 12:59 PM
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why? please explain.
also, what about a wrap drive?

phinds
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Feb18-14, 01:17 PM
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Beat the speed of light


Quote Quote by henrywang View Post
why? please explain.
also, what about a wrap drive?
"Why" is not a question that physics answers. "What does it do" and "how does it work" are the kind of questions physics answers. "Why questions" just lead to more "why questions" at which point religious folks say "god" and physicists say "damned if I know".

Warp drives do not exist.
henrywang
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Feb18-14, 01:31 PM
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Quote Quote by phinds View Post
"Why" is not a question that physics answers. "What does it do" and "how does it work" are the kind of questions physics answers. "Why questions" just lead to more "why questions" at which point religious folks say "god" and physicists say "damned if I know".

Warp drives do not exist.
OK... how does the object do not go beyond the speed of light given that there is infinite lengths for acceleration?
jbriggs444
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#6
Feb18-14, 01:49 PM
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If the acceleration is caused by a constant force then one reason is that the resulting acceleration becomes less and less as the accelerating object gets nearer and nearer to light speed.

In the realm where special relativity applies, F = ma and p = mv are no longer accurate.

Instead, F = dp/dt and p = m gamma v.

Where gamma is given by 1/sqrt(1-v2/c2)

If you want to contrive a constant acceleration by something like a uniform gravity field then you get different complexities that I am not competent to explain. Things like a Rindler horizon.
ag048744
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Feb18-14, 02:10 PM
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Quote Quote by phinds View Post
"Why" is not a question that physics answers. "What does it do" and "how does it work" are the kind of questions physics answers. "Why questions" just lead to more "why questions" at which point religious folks say "god" and physicists say "damned if I know".

Warp drives do not exist.
See this video with feynman : He clearly explains the problem with why? : http://www.youtube.com/watch?v=wMFPe-DwULM
phinds
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Feb18-14, 02:26 PM
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Quote Quote by ag048744 View Post
See this video with feynman : He clearly explains the problem with why? : http://www.youtube.com/watch?v=wMFPe-DwULM
Yes, that's one of my favorites and has been referenced on this site many times. There is an abbreviated version (cropped from this one) that is only a minute or so long, where he is JUST discussing the "why".
PeroK
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#9
Feb18-14, 02:39 PM
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I was brought up in Scotland, where "how" is often used instead of "why". I only noticed it when I moved to England. So, for me, "how" and "why" don't have the same linguistic difference that they may for others.

In Scotland you could say something like "how are you not going?". Which means "why are you not going?"!

Or, of course, "how can you not travel faster than light?"!
phinds
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Feb18-14, 02:47 PM
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Quote Quote by PeroK View Post
In Scotland you could say something like "how are you not going?". Which means "why are you not going?"!
Yeah, this kind of translation issue, or difference in dialects, is something I've noticed in many situations. For example, my wife is from Pennsylvania and says (Pennsylvania Dutch style) "let it outside" when she means what the rest of us would mean if we said "leave it outside" (talking about something that is already outside). So I would say, "let the dog outside and then leave it outside" and she would say "let the dog outside and then let it outside". Very confusing.

I once had a German teacher who, when I told him I was going on a trip, said "what are you going with?" when he meant "what are you taking with you?".

This kind of stuff just goes on and on.
SteamKing
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#11
Feb18-14, 03:15 PM
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Quote Quote by PeroK View Post
I was brought up in Scotland, where "how" is often used instead of "why". I only noticed it when I moved to England. So, for me, "how" and "why" don't have the same linguistic difference that they may for others.

In Scotland you could say something like "how are you not going?". Which means "why are you not going?"!

Or, of course, "how can you not travel faster than light?"!
Did you meet a lot of people in Scotland with the monniker 'henrywang' who were also interested in 'wrap drives'?
crownedbishop
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#12
Feb18-14, 03:20 PM
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In my personal experience, "why does it happen?", and "how does it happen" are physics questions. "Why does it happen?", is usually a metaphysics question. Perhaps you should read some Aristotle for that. Actually, an object can go faster than c. If you're talking about an object in a gravitational field with an infinitely long radius, I would think that you would be talking about an alternative universe. Surely, the same laws of physics might not apply.
Jimmy
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#13
Feb18-14, 03:23 PM
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Quote Quote by henrywang View Post
If a a object is falling in a gravity field with infinitly long radius. can it eventually travel faster than the speed of light?
If you are launched from the surface of a planet at escape velocity, your speed would reach 0 at infinity. If you freely fall toward a mass from an infinite distance--with an initial v=0--you would impact the surface at escape velocity.
Drakkith
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#14
Feb18-14, 05:16 PM
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Quote Quote by henrywang View Post
OK... how does the object do not go beyond the speed of light given that there is infinite lengths for acceleration?
There's a number of reasons.

1. An infinite length of acceleration is easy to think about. Just look at escape velocity. It is the velocity an object needs in order to escape the Earth's gravitational pull. In other words, it is how fast an object needs to go to get from the Earth's surface to an infinite distance. But how is this possible if gravity is pulling on it the whole way? The answer lies in the fact that the force of gravity falls off with distance. So if you launch an object away from the Earth fast enough, gravity won't be able to slow it down fast enough to keep up with how quickly the force falls off. Its speed will continue to decrease as it gets further and further away, but it will never hit zero.

So any realistic situation in which you would have an infinite distance to accelerate would be subject to the same laws. An object attracted to another object through gravity will never reach an infinite velocity because of how weak the attraction is at great distances.

Note that there is no realistic scenario in which you could apply a steady force for an infinite distance or time.

2. Even in a situation where you could apply a steady force for an infinite amount of time, the rules of special relativity show us that this still wouldn't result in a velocity equal to c. That's simply not the way the universe works.
Habeebe
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#15
Feb19-14, 09:34 AM
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If you constantly push on an object you are always putting in a finite amount of energy given the amount of time that you've pushed it is finite. Special relativity gives:

Kinetic Energy = T = mc2(γ-1) = [itex]\frac{mc^2}{\sqrt{1-v^2/c^2}} - mc^2[/itex]
If we get close to the speed of light, then that's the limit as v approaches c. If you take that limit v→c, then K→∞. So to get to lightspeed we need infinite energy. There's no way to give an object infinite energy with a finite amount of force. So you would need to run your experiment for an infinite amount of time to reach light speed.

Alternatively, you can look at the addition formula for velocities. If v is our original velocity, u the velocity we add to v, and u' the final velocity, we have:

[itex] u' = \frac {u-v} {1-\frac {uv}{c^2}} [/itex]

If I apply a force for some finite interval of time and start below the speed of light, then u' will never be equal to or greater than c. You can repeat this addition as many times as you want and you'll never get to c. So, say I take the amount of velocity that the gravitational field adds every second and keep adding it to the velocity using this formula, the sequence will look like .99, .999, .9999, .99999, but it'll never get to or above 1 for any finite number of additions.

Both of these break down if you have an infinite time in which to perform the experiment, but this isn't a realistic scenario, so don't expect physics to answer such a question.


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