# Speed of the outside of a wheel faster than the speed of light

• Sciencepoo
In summary: The "beam" of laser light is only conceptualized as a single thing in a simplistic mental model.It is no more a single object than a spray of bullets from a machine gun.By analogy to your demo, I could spin the barrel of a machine gun from North to South and claim the spray of bullets is traveling at 20 times the speed of sound.
Sciencepoo
I'd like to know if anybody can tell me either;
How large a wheel would have to be for the outer edge to travel faster than the speed of light if powered by a motor that's around now.
We'll say the wheel is in outer space to eliminate drag and such

Don't think matter can move faster than light ... Einstein and all that.

Hello Sp, !

davenn and russ_watters
Sciencepoo said:
Summary: A wheel that can travel ftl

I'd like to know if anybody can tell me either;
How large a wheel would have to be for the outer edge to travel faster than the speed of light
It is not possible to construct such a thing, even in principle. It will necessarily disintegrate or distort so that nothing travels faster than light.

There is no way to trick your way round that speed limit.

davenn, russ_watters and Dale
Hypothetically speak even if we could make a wheel big enough (however big that may be,) I am not sure any motor we have today would have enough torque to turn it due to it's size.

Sciencepoo said:
Summary: A wheel that can travel ftl

How large a wheel would have to be for the outer edge to travel faster than the speed of light if powered by a motor that's around now.
As @Ibix mentioned it will necessarily disintegrate before it reaches c. However, another issue is that it would require an infinite amount of energy. So a motor could run for any amount of time and still not have produced sufficient mechanical energy.

russ_watters and Ibix
MikeeMiracle said:
Hypothetically speak even if we could make a wheel big enough (however big that may be,) I am not sure any motor we have today would have enough torque to turn it due to it's size.
In principle you can turn an arbitrarily large wheel with an arbitrarily small motor. You just put the whole thing in zero g in vacuum and let conservation of angular momentum do its thing. It'll just take an arbitrarily long time.

The problem is that no matter how powerful the motor or how large the wheel, you cannot get the rim to exceed lightspeed even in principle.

Ibix said:
The problem is that no matter how powerful the motor or how large the wheel, you cannot get the rim to exceed lightspeed even in principle.
If you discard the requirement that anything physical is made to exceed light speed, one can accomplish the feat quite conveniently.

Take a laser pointer and assume (for the sake of argument) that its beam is tightly collimated. Point it at the right edge of the moon. Flick the pointer so that it points to the left edge of the moon. Do this in less than 10 milliseconds and the illuminated spot on the moon will have traveled from the right edge to the left edge at a speed faster than light.

https://www.universetoday.com/10914...ove-faster-than-light-and-why-it-really-isnt/

Yes, it's "information" that cannot travel faster than the speed of light as far as I understand it.

MikeeMiracle said:
Yes, it's "information" that cannot travel faster than the speed of light as far as I understand it.
Objects are/carry information. Physical objects can't travel faster than light.

MikeeMiracle said:
Hypothetically speak even if we could make a wheel big enough ...

jbriggs444 said:
Take a laser pointer and assume (for the sake of argument) that its beam is tightly collimated. Point it at the right edge of the moon. Flick the pointer so that it points to the left edge of the moon. Do this in less than 10 milliseconds and the illuminated spot on the moon will have traveled from the right edge to the left edge at a speed faster than light.

I'm really not sure what this has to do with the thread topic but it's flawed.

The "beam" of laser light is only conceptualized as a single thing in a simplistic mental model.
It is no more a single object than a spray of bullets from a machine gun.

By analogy to your demo, I could spin the barrel of a machine gun from North to South and claim the spray of bullets is traveling at 20 times the speed of sound.

russ_watters
Sciencepoo said:
How large a wheel would have to be for the outer edge to travel faster than the speed of light if powered by a motor that's around now.
This answer cuts to the chase of what you're asking. It grants every possible engineering objection - from fuel to speed to material strength*. And yet the edge will never reach c, let alone exceed it.

*Except one: the theory of relativity itself prohibits the existence of infinitely-strong/infinitely-rigid materials.

Q: Why won't it reach c?

A: Like all things, the wheel is subject to relativity. As the edge approaches relativistic speed, it will length contract, just like anything else. Increasing speed will get the edge closer to c but will never exceed it.

Yes, this will cause the wheel to distort in shape, since the non-relativistic inner parts will not likewise get length-contracted. Yes, it will actually disintegrate - but not simply because the material is not strong enough to withstand the forces - it will disintegrate because relativistic effects will distort it.You'll want to read up on Bell's Spaceship Paradox. That one is two spaceships in a line, but there's a derivative experiment (link, anyone?), set up like so:

Tie a bunch of spaceships into a circle, nose-to-tail, with pieces of string. Space the ships so the string is taut. Set the spaceships chasing each around the circle at relativistic speeds.

Q: We know the spaceships will shrink in length, but will the strings break?

A: Yes. Any rigid loop, when accelerated to a rotation of relativistic velocity, will be contracted. Its rotational speed will approach, but never reach, c.

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DaveC426913 said:
By analogy to your demo, I could spin the barrel of a machine gun from North to South and claim the spray of bullets is traveling at 20 times the speed of sound.
Yes, the point of impact of the bullets could be made to move at pretty much any desired speed, including faster-than-light. As you point out, that "point of impact" is not anything physical traveling from point A to point B.

russ_watters

## 1. What is the concept of the speed of the outside of a wheel being faster than the speed of light?

The concept of the speed of the outside of a wheel being faster than the speed of light is a hypothetical scenario in which the outer edge of a rotating wheel is moving faster than the speed of light, which is considered to be the universal speed limit according to Einstein's theory of relativity.

## 2. Is it possible for the outside of a wheel to exceed the speed of light?

No, it is not possible for the outside of a wheel to exceed the speed of light. According to Einstein's theory of relativity, the speed of light is the maximum speed at which any object can travel. This means that no physical object, including the outer edge of a wheel, can travel faster than the speed of light.

## 3. Why is the speed of light considered to be the universal speed limit?

The speed of light is considered to be the universal speed limit because it is a fundamental constant in the universe and is the maximum speed at which any object can travel. This is due to the fact that as an object approaches the speed of light, its mass increases and it requires an infinite amount of energy to accelerate it further.

## 4. What would happen if the outside of a wheel did exceed the speed of light?

If the outside of a wheel did exceed the speed of light, it would violate the laws of physics as we know them. It would also lead to paradoxes and contradictions, such as time travel and the breakdown of causality. This is why it is considered impossible for the outside of a wheel to exceed the speed of light.

## 5. Are there any real-life applications or implications of the concept of the speed of the outside of a wheel being faster than the speed of light?

No, there are no real-life applications or implications of the concept of the speed of the outside of a wheel being faster than the speed of light. This is because it is a hypothetical scenario that goes against our current understanding of physics and the laws of the universe.

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