Incredibly huge inconsistency of modern physics

wogoga

Critical Thinker
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Joined
Apr 16, 2007
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334
zosima said:
Mass-Energy equivalence means that even though a photon is massless it has energy
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This could be the most concise formulation of a central contradiction of modern orthodox physics: Equivalence between mass and energy on the one hand, but energy without mass on the other hand. How is it possible that educated persons accept such a huge inconsistency?

See also:
Cheers, Wolfgang
 
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You seem to be confusing rest mass with relativistic mass. Thanks for the web posts in German, though. I always enjoy reading that language.

Sincerely,
A semi-educated person
 
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...and also confusing "equivalence" and "equality".

How is it that educatated people...

Oh, never mind.

Life is too short.
 
Incredibly huge inconsistency of your knowledge of modern physics. Photons have an energy that is related to their frequency. They also have zero rest mass and so no rest energy.

Educated people know that there is no inconsistency.
 
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The idea that a photon has no mass while at rest (even though they apparently aren't ever at rest) but has a mass while moving at c is certainly weird. But that does not mean it isn't true.

LLH
 
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LordoftheLeftHand said:
The idea that a photon has no mass while at rest (even though they apparently aren't ever at rest) but has a mass while moving at c is certainly weird. But that does not mean it isn't true.

LLH
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E = M * C2, so mass and energy are related by the square of the speed of light. Total energy equals potential energy plus kinetic energy. For an object with rest mass that rest mass is potential energy so EREST = MREST * C2. The kinetic energy of an object is related to its relative velocity but that kinetic energy also represents mass EKINETIC = MKINETIC * C2. This is often referred to as the change in or delta mass. The total mass, often referred to as relativistic mass or MV (mass at velocity), is just the rest mass plus the kinetic (or delta) mass or the total energy (potential plus kinetic) divided by the speed of light squared. As a varying amplitude of electromagnetic fields or a wave packet of electromagnetic radiation a photon has no rest energy, it is purely kinetic and therefore has no rest mass only relativistic mass, so its total (or relativistic) mass equals its kinetic (or delta) mass . What is weird or inconsistent about that?
 
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This could be the most concise formulation of a central contradiction of modern semnantic mistakes: Equivalence between fur and dogs on the one hand, but dogs without fur on the other hand. How is it possible that educated persons accept such a huge inconsistency?
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Hmmm?
 
The Man said:
E = M * C2, so mass and energy are related by the square of the speed of light. Total energy equals potential energy plus kinetic energy. For an object with rest mass that rest mass is potential energy so EREST = MREST * C2. The kinetic energy of an object is related to its relative velocity but that kinetic energy also represents mass EKINETIC = MKINETIC * C2. This is often referred to as the change in or delta mass. The total mass, often referred to as relativistic mass or MV (mass at velocity), is just the rest mass plus the kinetic (or delta) mass or the total energy (potential plus kinetic) divided by the speed of light squared. As a varying amplitude of electromagnetic fields or a wave packet of electromagnetic radiation a photon has no rest energy, it is purely kinetic and therefore has no rest mass only relativistic mass, so its total (or relativistic) mass equals its kinetic (or delta) mass . What is weird or inconsistent about that?
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Yeah yeah, i've read all that before. Even though it's true it's still weird. :p

LLH
 
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To be fair, wogoga's "claims" make just as much sense in German.

(I don't read German.)
 
[latex]E = m c^2[/latex]
is just a special case that applies only for particles without momentum, or systems without net momentum. Photons are outside of its validity since they're never at rest.

The full equation is:

[latex]E^2 - (p c)^2 = (m c^2)^2[/latex]

If you plug in rest mass m=0, you'll get the correct value of a photon's energy as

[latex]E = pc[/latex]
 
Doesn't all this equation-writing rather miss the misunderstanding inherent in the claim
Equivalence between mass and energy on the one hand, but energy without mass on the other hand.
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...where wogoga clearly indicates that the word "equivalence" is the problem.

English, not Physics.
 
Either can be corrected if there is sufficient intelligence and access to data in the correctee.
 
Somehow I get the impression that wogaga would be happier to stick with the idea that everybody else is stupid.
 
elqarak said:
is just a special case that applies only for particles without momentum, or systems without net momentum. Photons are outside of its validity since they're never at rest.
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No there is nothing special about E = M*C2 and you demonstrate that.

Sorry but for some reason I could not quote you directly so I had to resort to a cut and paste, loosing the equations and formatting you posted.

Regardless, the final equation of you post is E = pc or the energy of the photon is equal to its momentum times the speed of light. Since the momentum of the photon is p = MV * C or the relativistic mass of the photon times the speed of light. This makes the equation for the energy of a photon as E = MV * C2 just as valid as the form you presented. None of these variations in the form of the equation says anything different or is in any way special.

ETA: You could also write the momentum of the photon as Planck’s constant over the wavelength but that is just another form that is equally valid.
 
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Henners said:
Doesn't all this equation-writing rather miss the misunderstanding inherent in the claim ...where wogoga clearly indicates that the word "equivalence" is the problem.

English, not Physics.
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wogoga said:
Equivalence between mass and energy on the one hand, but energy without mass on the other hand.
Click to expand...

The real misunderstanding I see in the claim is the bit about “energy without mass”, so the problem seems to be with wogoga’s “other hand”.
 
The irony, as usual, is that someone is arguing against basic principles of physics on the Internet... which they could not do unless the basic principles of physics are exactly what scientists say they are.
 
The Man said:
The real misunderstanding I see in the claim is the bit about “energy without mass”, so the problem seems to be with wogoga’s “other hand”.
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Those of us who prefer to let the word "mass" refer to the rest mass of a particle would prefer to say it's the other way round. I'm not saying that you're wrong. It's a matter of taste.

This is how I've been thinking about these things since I read chapter 2 of Weinberg's QFT book: The (four-)momentum operators are defined as the generators of translations in time and space. They commute with each other, so we can find simultaneous eigenstates of all four. Those states are also eigenstates of

[latex]\footnotesize P^2=-(P^0)^2+(P^1)^2+(P^2)^2+(P^3)^2=-H^2+\vec P^2[/latex]

The vectors in a subspace that's invariant under Lorentz transformations represent the possible states of a physical system that consists of exactly one particle. Every momentum eigenstate in such an invariant subspace must have the same eigenvalue of P2, since P2 commutes with all the generators of the Poincaré group. This eigenvalue apparently represents an intrinsic property of the partice. Let's write the eigenvalue as -m2 and call m "mass". This means that

[latex]\footnotesize H^2=\vec P^2+m^2[/latex]

where the last term must be interpreted as m2 times the identity operator. When this operator acts on a momentum eigenstate, the result is

[latex]\footnotesize E^2=\vec p^2+m^2[/latex]

This is in units such that c=1. Restoring factors of c, we get

[latex]\footnotesize E^2=\vec p^2 c^2+m^2 c^4[/latex]

Now what's "relativistic mass"? If we simply write the left-hand side as (something)2c4, then the "something" must have dimensions of mass. Let's call the magnitude of this something "relativistic mass".

When you look at it from this point of view, the concept of relativistic mass seems pretty pointless and irrelevant.
 
I'll admit my original statement was poorly phrased and I should have said 'rest mass', I apologize if my statement was confusing. Although, I don't think it was particularly problematic if taken in the context of the discussion.
 
If you replace mass with rest mass, where is the inconsistency? A photon has mass, energy and momentum, but not rest mass. What's the problem?
 
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Reality Check said:
A photon has no rest mass or mass. It has energy and momentum. These can be considered to as "relativistic mass".
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I love this stuff, even if it is hard to wrap my head around it. :boxedin:

Isn't momentum mass * velocity? (OK, I'm going all the way back to my high school physics). I get the feeling from what has been said in other posts, my high school definition is lacking, but the definition in high school was p=mv.
 
a_unique_person said:
I love this stuff, even if it is hard to wrap my head around it. :boxedin:

Isn't momentum mass * velocity? (OK, I'm going all the way back to my high school physics). I get the feeling from what has been said in other posts, my high school definition is lacking, but the definition in high school was p=mv.
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You may want to read the link which explains all of this. p=mv is only for particles with mass and as the article states:
In empty space, the photon moves at c (the speed of light) and its energy E and momentum p are related by E = cp, where p is the magnitude of the momentum.
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I think that it bother some people that a photon can have mass because it moves at the speed of light but no rest mass.

They want the universe to agree with their preconceived notions.
 
a_unique_person said:
Isn't momentum mass * velocity? (OK, I'm going all the way back to my high school physics). I get the feeling from what has been said in other posts, my high school definition is lacking, but the definition in high school was p=mv.
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That's the pre-relativistic definition of the momentum of a massive particle. Special relativity changes that definition to

[latex]\footnotesize $\vec{p}=\gamma m \vec v$[/latex]​

where

[latex]\footnotesize \gamma=\frac{1}{\sqrt{1-\frac{v^2}{c^2}}}[/latex]​

Note that we recover the pre-relativistic definition in the limit [latex]\footnotesize c\rightarrow\infty[/latex].

The m above is the particle's mass. Some people prefer to call it the rest mass. They would call the quantity [latex]\footnotesize\gamma m[/latex] the mass (or relativistic mass). They would also write m0 instead of m, and they would write m instead of [latex]\footnotesize\gamma m[/latex].
 
Fredrik said:
Those of us who prefer to let the word "mass" refer to the rest mass of a particle would prefer to say it's the other way round. I'm not saying that you're wrong. It's a matter of taste.
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Oh, I agree completely and that was primarily my point, the matter of taste. wogoga taking the mass energy equivalence on one hand and then only considering invariant mass on the other. Kind of like playing classical music and rap at the same time and then wondering why it sounds so bad. Mass is simply a value having the units of (or equivalent) Newton Second2 Meter-1. As far as tastes go my taste varies depending on what I am tying to find out. However, although I agree that relativistic mass can seem irrelevant, as long as the math works I dislike discarding anything as irrelevant since you could miss an important relationship, but that is just my taste. It is in fact that aspect which can also show us a photon has a frame dependent mass. With wavelength (and thus momentum) dependent on relative motion between the receiver and the light source and with the speed of light frame invariant then with the p = m * V relationship (which may be technically incorrect for a photon but the math still works) we know that the mass (or that Newton Second2 Meter-1 something) of the photon must also be frame dependent.
 
Fredrik said:
That's the pre-relativistic definition of the momentum of a massive particle. Special relativity changes that definition to
latex.php
where
latex.php
Note that we recover the pre-relativistic definition in the limit
latex.php
.

The m above is the particle's mass. Some people prefer to call it the rest mass. They would call the quantity
latex.php
the mass (or relativistic mass). They would also write m0 instead of m, and they would write m instead of
latex.php
.
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So what happens when v=c?
 
a_unique_person said:
So what happens when v=c?
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p becomes infinite. Since this means that an infinite impulse would be required to impart sufficient momentum for a particle to travel at c, this shows that a particle of non-zero rest mass cannot travel at the speed of light.

Just expanding a little on Reality Check's answer.

Dave
 
I wrote:

Equivalence between mass and energy on the one hand, but energy without mass on the other hand.​

Dancing David brought forward this analogy:

Equivalence between fur and dogs on the one hand, but dogs without fur on the other hand.​

If we take seriously the equivalence between fur and dogs we conclude:

  • a fur without corresponding dog or a dog without corresponding fur is impossible
  • a fur corresponds nevertheless to a dog without a fur
  • fur and fur are two different concepts


zosima said:
I'll admit my original statement was poorly phrased and I should have said 'rest mass', ...
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Zosima's original statement:

Mass-Energy equivalence means that even though a photon is massless it has energy​

If we replace mass with restmass we get:

Restmass-Energy equivalence means that even though a photon has no restmass it has energy​

This version is obviously wrong, because there is no equivalence between restmass and energy. Equivalence only reigns between (relativistic) mass and energy. The alternative

Equivalence between (relativistic) mass and energy means that even though a photon has no restmass it has energy​

doesn't make a lot of sense, because of the confusion between two different mass-concepts (mass and restmass).


Cheers, Wolfgang

Comments on FAQ - Does light have mass? (post 1, post 2, post 3)
 
wogoga said:
I wrote:
Equivalence between mass and energy on the one hand, but energy without mass on the other hand.
​
..snip..
Zosima's original statement:
Mass-Energy equivalence means that even though a photon is massless it has energy
​
If we replace mass with restmass we get:
Restmass-Energy equivalence means that even though a photon has no restmass it has energy
​
This version is obviously wrong, because there is no equivalence between restmass and energy. Equivalence only reigns between (relativistic) mass and energy. The alternative
Equivalence between (relativistic) mass and energy means that even though a photon has no restmass it has energy
​
doesn't make a lot of sense, because of the confusion between two different mass-concepts (mass and restmass).


Cheers, Wolfgang

Comments on FAQ - Does light have mass? (post 1, post 2, post 3)
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There is no such thing as "restmass". A particle with mass has a "rest mass". A particle with mass that is moving has a relativistic mass that is its rest mass multiplied by the Lorentz factor.

The original posting by zosima was "Mass-Energy equivalence means that even though a photon is massless it has energy" and that is inexact since mass-energy equivalence is usually taken to be E=mc2 and that is the rest energy of a particle. A photon is never at rest.

There is no confusion between mass and rest mass, just in the expected conventions of their their use.
A photon has energy. We know that through their interactions with matter, especially the photoelectric effect.
 
wogoga said:
I wrote:
Equivalence between mass and energy on the one hand, but energy without mass on the other hand.​
Dancing David brought forward this analogy:
Equivalence between fur and dogs on the one hand, but dogs without fur on the other hand.​
If we take seriously the equivalence between fur and dogs we conclude:
  • a fur without corresponding dog or a dog without corresponding fur is impossible
  • a fur corresponds nevertheless to a dog without a fur
  • fur and fur are two different concepts



Zosima's original statement:
Mass-Energy equivalence means that even though a photon is massless it has energy​
If we replace mass with restmass we get:
Restmass-Energy equivalence means that even though a photon has no restmass it has energy​
This version is obviously wrong, because there is no equivalence between restmass and energy. Equivalence only reigns between (relativistic) mass and energy. The alternative
Equivalence between (relativistic) mass and energy means that even though a photon has no restmass it has energy​
doesn't make a lot of sense, because of the confusion between two different mass-concepts (mass and restmass).


Cheers, Wolfgang

Comments on FAQ - Does light have mass? (post 1, post 2, post 3)
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Ah, now you make complete sense! Have you considered writing a book in which you use color to elucidate the principles of physics, like Oliver Byrne did with Euclidean geometry?
 
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Reality Check said:
Educated people know that there is no inconsistency.
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I have to say this isn't quite true. People educated in physics know there's no inconsistency. But I would say that at least many people educated in other fields would trust the physics dudes when they say there is none.
 
I think some of the problem and weirdness wogoga is experiencing comes from the applied units vs the actual meaning of what those units represent. Let’s take Energy for example measured in units of Newton Meters, or Joules as such it is a force multiplied by the distance that force is applied through. Torque also takes the same form of units Newton Meters but has a different meaning, in this case it is a force multiplied by the distance from the rotational center (or radius) that the force is applied. Same units different meanings, to convert torque to energy you would need the rotational angle during the force application in radians and multiply it by the radius to get the cord subtended by that angle or in other words the actual distance the force was applied then multiply that times the force.

A similar thing is occurring here, Mass is measured in units of Kilograms or Newton Second2 Meter-1, some values can take that form of units yet may not adhere to the specific aspects that generate those units and thus not technically be mass. The property of mass that defines these units is Newton’s second law of motion F = m*a or Force equals mass times acceleration. We can convert this to represent mass as m = F / a or mass equals Force divided by acceleration. With the units of mass as Kilograms, force as Newtons, and the inverse of acceleration as Second2 Meter-1 the result is Kg = Newton Second2 Meter-1. More importantly though, is the meaning of the units or Force per acceleration. As a photon does not have the capability of acceleration (changing velocity) this specific aspect of mass does not apply. The energy of the photon can still be represented in this form of units that we use for mass (since it is just a frame invariant conversion) and all the normal equations will work out mathematically, but since the photon lacks the ability to accelerate the true meaning of the units is not applicable. With the units of acceleration as Meter Second-1 the “acceleration” of a photon becomes the speed of light times the frequency of the photon. So what we might represent as the units of “acceleration” for a photon is simply the Doppler shift of frequency due to relative motion and not the result of any real force applied to the photon.
 
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