TL;DR

I thought of a disk rotating freely in space at 60 RPM, for example, as a way to move gross matter at and beyond the speed of light.
A point on the disk at a radius of 5/π meters would be moving at a speed of 10 m/sec, ∴ a point on the disk at a radius of (15x10⁷)/π meters should be moving at a speed of 3x10⁸ m/sec.

I thought of a disk rotating freely in space at 60 RPM, for example, as a way to move gross matter at and beyond the speed of light.

A point on the disk at a radius of 5/π meters would be moving at a speed of 10 m/sec, while a point on the disk at a radius of 50/π meters would be moving at a speed of 100 m/sec, right? So it would follow that a point on the disk at a radius of (15x10⁷)/π meters should be moving at a speed of 3x10⁸ m/sec.

I imagine that people who spend far more time cogitating on than I do would readily recognize where this construct fails. I look forward to reading your responses.

Ibix

Disintegrate, as in atoms converting into photons? If so, then the disk itself would appear to us observing as a solid disk ringed by light...?

Ibix

Thank you for your replies.

The centrifugal force at the edge of the disk is proportional to the radius of the disk, which in this case is about 30,000 miles. Have you calculated that force? It might be very large. The disk would have to withstand that force.

PeroK

Last edited: Mar 23, 2026

PeroK

FactChecker said:

The centrifugal force at the edge of the disk is proportional to the radius of the disk, which in this case is about 30,000 miles. Have you calculated that force? It might be very large. The disk would have to withstand that force.

Yes, nearly 48,000 Km. If the force at that radius was too great for the disk's material to hold together, then the material would fly off at a speed somewhere around c...

aLeaf said:

If the force at that radius was too great for the disk's material to hold together,

Relativity says it must be. Relativity imposes a finite limit on the strength of materials, and that limit ensures that it is impossible to spin any material such that the speed of its rim would be ##c## or greater. The material must fail before that point is reached.

PeroK said:

Why not simply accelerate a particle at constant acceleration until it surpasses ##c##? That's what you are doing to a particle on the edge of your disk.

A rotating disk is an easier construct. Perhaps a method could be devised to engineer a disk of smaller size, commence spinning, and then gradually add more material at the periphery until the desired radius is reached...

PeterDonis said:

Relativity says it must be. Relativity imposes a finite limit on the strength of materials, and that limit ensures that it is impossible to spin any material such that the speed of its rim would be ##c## or greater. The material must fail before that point is reached.

Perhaps.... but I am someone who does not accept theoretical impossible limits without testing them...

aLeaf said:

I am someone who does not accept theoretical impossible limits without testing them...

Well, we don't have an actual test lab here, so all we can tell you is what the theory says.

PeterDonis said:

Relativity says it must be. Relativity imposes a finite limit on the strength of materials, and that limit ensures that it is impossible to spin any material such that the speed of its rim would be ##c## or greater. The material must fail before that point is reached.

The limits of the disc material strength could be overcome by applying the required centripetal forces externally. But even those centripetal forces tend to infinity, as the rim approaches a tangential speed of c.

aLeaf said:

A rotating disk is an easier construct. Perhaps a method could be devised to engineer a disk of smaller size, commence spinning, and then gradually add more material at the periphery until the desired radius is reached...

You could counter the above limit by making the radius tend to infinity, instead of increasing the angular velocity. But then you are effectively just moving in a straight line, which is simpler to analyse anyway.

A.T. said:

The limits of the disc material strength could be overcome by applying the required centripetal forces externally.

At that point the disc is not a single object, each piece of it to which an external force is applied is a separate, independent object. And then of course the very concept of "material strength" no longer applies. Effectively you've broken the disc already and now you're just up against relativistic kinematics, which, as you say, still stops you from accelerating anything to ##c##.

aLeaf said:

Perhaps.... but I am someone who does not accept theoretical impossible limits without testing them...

Please report back with your test results!

PeroK

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PeterDonis said:

Well, we don't have an actual test lab here, so all we can tell you is what the theory says.

Maybe there is some old, abandoned lab space somewhere on the server where we could conduct thought experiments...?

SiennaTheGr8 said:

Please report back with your test results!

This thread is my lab...

PeroK said:

The idea of a disk confuses the issue that within the disk you have particles being accelerated towards ##c##. Each of those particles has kinetic energy tending to infinity. It doesn't matter how complex your overall structure is, a particle with mass cannot be accelerated to ##c##.

Note that if you use Newtonian physics, then nothing stops you accelerating a particle beyond ##c##. The question is, therefore, whether the Newtonian equation for kinetic energy is correct. Or, whether the relativistic kinetic energy is correct.

This has been tested many times. All of modern particle physics uses relativistic energy and momentum.

There is no longer any possibility that Newtonian physics is universally valid.

That sounds very finalistic, relatively speaking

PeroK said:

Then you'll have to do a degree in experimental physics!

Just as soon as I finish my post-doc in endocannabinoid pharmacodynamics.

aLeaf said:

This thread is my lab...

We've already given you the results that this lab produces--they're the results that relativity predicts.

I wonder... what's the speed of sound in unobtainium?

Ibix

Last edited: Mar 23, 2026

Ibix