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Author Topic: Is mass change with speed a flaw in the theory of special relativity?  (Read 415 times)

Offline thedoc

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SIBAPRASAD DAS asked the Naked Scientists:
   Einstein in his STR concluded mass changes with the speed and tends to infinity as speed of the object approaches the speed of light . He inferred on the basis of electro dynamics and Lorentz trans formation . But did he ever think that the driving agent's speed matters the most ? Scientists always tried to speed up particle with the electromagnetic field whose own speed limit is the speed of light . So aslong as they would try with the particle accelerator of electromagnetic field would come to the same conclusion and never be able to reach the speed of . Think otherwise .
 Mass never change .
What do you think?
« Last Edit: 11/10/2016 19:55:20 by chris »


 

Offline Janus

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Re: A possible flaw of STR - Mass changes with speed
« Reply #1 on: 11/10/2016 19:51:14 »
SIBAPRASAD DAS asked the Naked Scientists:
   Einstein in his STR concluded mass changes with the speed and tends to infinity as speed of the object approaches the speed of light . He inferred on the basis of electro dynamics and Lorentz trans formation . But did he ever think that the driving agent's speed matters the most ? Scientists always tried to speed up particle with the electromagnetic field whose own speed limit is the speed of light . So aslong as they would try with the particle accelerator of electromagnetic field would come to the same conclusion and never be able to reach the speed of . Think otherwise .
 Mass never change .
What do you think?

Einstein's conclusion of the light speed limit was derived from the invariant nature of the speed of light.  Basically it comes down to that once you establish that there is a finite speed that is measured as being the same for all inertial frames, that speed is also the speed limit for the universe. How you attempt to reach that speed has no bearing on your inability to reach it.

But let's approach this from the practical example of a particle accelerator.  It is true that we use electromagnetic fields to get the particles up to speed.   But we also note that the greater the speed at which we want to accelerate the particle to, the greater the amount of energy we have to pump into those fields and this amount of energy matches what Einsteins predicted.  Now you might try to argue is that this increase in energy is due to the decreasing inefficiency of the fields acting on the particle as it gets closer to the speed of light, but hen you would have to explain where the excess energy did go.

In addition, if you are going to argue that it is the lack of the EM fields ability to push the particle up to light speed for the reason you suggest, then the particle after being accelerated up to light speed should have no more kinetic energy than what Newtonian Physics would predict for a particle moving at that speed.  However,we don't just stop with accelerating the particles up to near light speeds, we smash them in to things and examine the results.  The results of those experiments show that the kinetic energy of those particles well exceeds that predicted by Newton and agrees with That predicted by Einstein.  That extra energy we pumped electromagnetic fields went into the particle, but smaller and smaller amounts of that energy resulted in an increased speed. 

You are correct about one thing, in the modern view of Relativity, the Mass of the particle does not change.  This is not however due to any modification of the theory itself, but due to the change in convention.  At one time it was common to talk about "rest mass" and "Relativistic mass".  Relativistic mass was what increased as an object accelerated.  This became a bit cumbersome, and since it was known that the Relativistic Mass was just the mass equivalent of the Kinetic energy, it was decided that the term "mass" would only apply to the Rest or invariant mass, and relativistic mass would be just considered "energy".    In this way the mass of the particle is considered as constant, and it is its energy that increases by the rules of Relativity as the particle accelerates. 

Outside of the energy requirements, there is another line of reasoning that sets the speed of light as a limit.  It uses the addition of velocities.
We normally assume that velocities add linearly. Thus for instance, if we are traveling at a speed of w with respect to the road and throw a ball forward at a speed of v relative to ourselves, the ball will be moving at w+v with respect to the road.  Einstein showed that this was not the case, and due to the invariant nature of the speed c, the correct equation would be  (u+v)/1+uv/c^2).

Now as long as u and v are small compared to c, the answer comes out to be very very close to u+v. So close, that in normal life speeds, we could never measure the difference.

But is does become noticeable as v and w become larger.  The thing to note is that as long as you start with values of u and v that are smaller than c, the answer will be smaller than c. So for example, if you start out from A at 0.5c and then at some point drop a marker that continues t move at 0.5 relative to A, and then accelerate until you are, by your measurement, moving at 0.5c relative to the marker, you would find that you measure your speed relative to A as being only 0.8c.  If you drop another marker, and accelerate to 0.5c relative to it, you will now be moving at ~0.92857c.   You can keep dropping markers and accelerating to 0.5c with respect to them forever and you will never reach a speed of c relative to A.
« Last Edit: 11/10/2016 21:12:27 by Janus »
 

Online alancalverd

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Far from being a flaw n the theory, it's an experimental fact.
 
The following users thanked this post: PmbPhy

Offline evan_au

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Quote from: SIBAPRASAD DAS
Scientists always tried to speed up particle with the electromagnetic field whose own speed limit is the speed of light
It is true that the microwave acceleration fields inside a particle accelerator only propagate at the speed of light.

But this is not the only measure of the speed of a wave - you can also measure the phase velocity and group velocity, and these are not limited to c. (But don't get your hopes up - you can't transmit information or energy faster than c.)

In a particle accelerator, a bunch of charged particle (eg protons or electrons) reacts to a local electric field that always attracts it in the forward direction, always causing it to increase in speed. Naturally, the frequency and phase of this local electric field must be carefully matched to the position and velocity of the particle bunch, or it won't accelerate them to a useful velocity - it would sometimes decelerate them.

It is quite possible to configure the phase of the adjacent microwave generators so that they would accelerate a particle traveling at 2c or 10c. But it would do you no good, because no matter how long you accelerate the particles, or how much energy you inject into them, they never exceed 1c.

See: https://en.wikipedia.org/wiki/Phase_velocity#Relation_to_group_velocity.2C_refractive_index_and_transmission_speed
 

Offline PmbPhy

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I had responded to the comments above last night. However I was very disappointed with the way that I expressed myself. I, unintentionally, came off as perhaps rude and condescending. I often use the term ignorant when I'm referring to comments and/or impressions formed with a lack of knowledge of the subject at hand. Unfortunately far too many people perceive the term ignorant as being synonymous as stupid. Even those who know the exact meaning of that term might get the impression that I meant to refer it them as such. However that was and has never been my intention. In fact if this is the same Janus that I ran into over a decade ago then I can tell you that Janus is anything but stupid. However a large number of physicists erroneously believe that relativistic mass is no longer in use. In fact that Usenet FAQ page on this subject was first written by a person who also erroneously had that belief. I had to convince the new physicist responsible for the maintenance of the Usenet FAQ that I am indeed correct on this point. With that in mind he deleted the old FAQ and rewrote it, correcting the mistake in the process. I myself took a great deal of effort actually researching this subject to make sure I had a complete and thorough knowledge of the subject and did a comprehensive literature search to make sure of what is actually being used.

Therefore I deleted my original response and will take more time to write a more thoughtful response and do my best to make sure that I don't appear to be rude.

Janus - I want to apologize to you if you go the impression that I was rude or was trying to insult you in any way, shape of form. Please accept my apology. :)

I will create another response and post it sometime this weekend, perhaps tomorrow.
 

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