Objects cannot have a velocity > c. But what about acceleration?

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Discussion Overview

The discussion revolves around the concept of acceleration in relation to the speed of light, particularly in the context of accelerating electrons. Participants explore whether it is possible for an object to have an acceleration greater than the speed of light and how this relates to the principles of relativity.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • Some participants propose that while an electron can be accelerated, its increasing velocity leads to an increase in relativistic mass, which slows down further acceleration, preventing it from reaching the speed of light.
  • Others argue that the question of whether acceleration can exceed the speed of light is meaningless, as acceleration and velocity are distinct concepts measured in different units.
  • A participant mentions that special relativity does not limit acceleration itself but suggests practical limits based on physical constraints like power requirements and material stress.
  • Some participants calculate hypothetical scenarios where an object could achieve high accelerations, such as going from rest to 0.9c in a short time, leading to discussions about the implications of such calculations.
  • There is a contention over the interpretation of the original question, with some asserting that it was poorly worded while others seek clarification on the intended meaning.

Areas of Agreement / Disagreement

Participants generally disagree on the interpretation of acceleration in relation to the speed of light, with multiple competing views on whether the original question was valid or meaningful. The discussion remains unresolved regarding the implications of acceleration exceeding certain values.

Contextual Notes

Limitations include varying interpretations of the original question, assumptions about the definitions of acceleration and velocity, and the practical constraints on acceleration in real-world scenarios.

sakodo
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Ok I was doing a question about electrons and this question arose.

Imagine we have a tremendous, constant mechanical force used to "push"(accelerate) an electron. At the moment the force is applied, the acceleration is easily greater than c in terms of magnitude. So what happens? Is the acceleration greater than c? But what happens after 1s? do we explain the electron's behaviour and velocity using relativity?

What I am thinking is that it IS possible to accelerate an electron, but as its velocity goes up, so does its mass. So eventually the electron would be accelerated slower and slower and thus its velocity would never reach c. Am I right here? Have I missed anything? Cheers
 
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sakodo said:
Ok I was doing a question about electrons and this question arose.

Imagine we have a tremendous, constant mechanical force used to "push"(accelerate) an electron. At the moment the force is applied, the acceleration is easily greater than c in terms of magnitude. So what happens? Is the acceleration greater than c? But what happens after 1s? do we explain the electron's behaviour and velocity using relativity?

What I am thinking is that it IS possible to accelerate an electron, but as its velocity goes up, so does its mass. So eventually the electron would be accelerated slower and slower and thus its velocity would never reach c. Am I right here? Have I missed anything? Cheers

c is a velocity. Acceleration is acceleration. The question can you have an acceleration greater then c is meaningless.
 
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So you can have an acceleration greater than the value of c right? Sorry man the question was confusing. What I meant was can objects have an acceleration greater than the value of c. I always had the impression that if objects cannot have a velocity greater than c, so does its acceleration.
 
Acceleration is acceleration and velocity is velocity. They are different things, measured in different units. Talking about "an acceleration greater than c" is like talking about "a sound greater than green".
 
The theory of special relativity does not in itself limit the acceleration of a physical object, but there will of course, depending on the situation, be practical limits as to how much acceleration you can give an object (power requirements, heating, maximum shear stress, and so on). I would think that you will be able to get some of the highest practical obtainable accelerations experiments involving particle physics, or perhaps in constructions like the railgun.
 
I agree to all the reserve of the preceeding posts.
An acceleration greater than c in magnitude only means that the object would reach the spped of light from rest in less that 1 second. That's all… And that's impossible.
Now, as a thought experiment, calculate the acceleration of an object which goes from rest to, say, 0.9c in 1/10 of a second. Well, that's trivial : the acceleration is already 9c m.s-2. Which is what you mean by “acceleration greater than c” :)
 
guerom00 said:
I agree to all the reserve of the preceeding posts.
An acceleration greater than c in magnitude...
That's still meaningless. Doesn't matter how many times you say it.
...only means that the object would reach the spped of light from rest in less that 1 second. That's all… And that's impossible.
An acceleration of 0 to C in 1 second isn't "an acceleration greater than c", but it does make more sense: it is 300,000 km/s/s. And no, it most certainly is not impossible. Particle accelerators far exceed that value of acceleration. Heck, it wouldn't be surprising to me if the electron gun in an ordinary TV exceeds that acceleration.
Now, as a thought experiment, calculate the acceleration of an object which goes from rest to, say, 0.9c in 1/10 of a second. Well, that's trivial : the acceleration is already 9c m.s-2. Which is what you mean by “acceleration greater than c” :)
It's good that you've now clarified mathematically what you mean, but now please start describing it correctly!
 
Don't fool yourself… Obviously, the question of the OP was “Is an acceleration of more than 299792458 m.s-2 possible ?”. At least, that's how I understand it…
The answer is yes. His choice of words was poor, that's all :)

PS : I was saying that it is impossible for a material object to reach the speed of light.
 
guerom00 said:
Obviously, the question of the OP was “Is an acceleration of more than 299792458 m.s-2 possible ?”.

Why is that more obviously correct than "Is an acceleration of more than 1 billion km/hr^2 possible ?”
 
  • #10
OK, ok… Maybe I misanderstood the OP… I don't know :)
Let's wait for sakodo to clarify :)
 

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