How can something be massless?

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Discussion Overview

The discussion centers around the concept of masslessness in particles, particularly photons and gluons, and how such entities can exist without mass. Participants explore theoretical implications, definitions of mass, and the relationship between mass, energy, and momentum.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • Some participants express confusion about how massless entities like photons and gluons can exist, given that they were taught all objects have mass.
  • One participant states that photons are massless due to the gauge invariance of electrodynamics, suggesting that mass is not straightforward to define.
  • Another participant argues that while photons have no rest mass, they possess energy due to their motion at the speed of light.
  • There are claims that light cannot be accelerated by a force and that its behavior is not related to force in the traditional sense.
  • Some participants assert that a photon must have mass because it has energy and moves, while others counter that energy is not the same as mass.
  • Discussions about the Higgs mechanism arise, with some participants questioning its applicability to massless particles and the implications of four-work on mass.
  • Several participants reference the equations relating energy and mass, such as E=mc², and debate their interpretations, particularly in the context of massless particles.
  • One participant suggests that light and mass could be viewed as different states of energy, while others emphasize that massless particles must travel at the speed of light.

Areas of Agreement / Disagreement

Participants do not reach consensus on the nature of mass and energy, with multiple competing views on whether massless particles can possess mass or if energy alone suffices. The discussion remains unresolved with ongoing debate about the definitions and implications of masslessness.

Contextual Notes

Participants express varying assumptions about the definitions of mass and energy, and the implications of relativistic physics on these concepts. The discussion includes references to specific physical theories and equations that may not be universally accepted or understood.

  • #31
DeepSeeded said:
I thought electrons were just the result of a resonance phenomenon of energy, I never thought of them being made of some sort of substance... I guess I am over my head, this post was originally on the classical physics forum.. now I am in quantum physics :redface:

I think you miss an important thing here: electrons HAVE mass, they are not "made up of mass".
 
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  • #32
malawi_glenn said:
I think you miss an important thing here: electrons HAVE mass, they are not "made up of mass".

I think of everything being made of up of energy or force and either mass is just an illusion or a conscience measurement of energy.

am I so far off? I have not studied the Higgs yet, getting there.
 
  • #33
You should perhaps wait til you can study quantum field theory at graduate level..

Also take string theory into consideration.
 
  • #34
DeepSeeded said:
I think of everything being made of up of energy or force and either mass is just an illusion or a conscience measurement of energy.

am I so far off? ...

Yes. Let's leave the philosophical speculations until after you get the math under your belt. Everyday intuition is not a reliable guide.
 
  • #35
I'm confused again. Daschaich said that light is a wave, not a partice. Don't photons have wave-particle duality? Also, what energy is Malawi talking about in post #27? Photons have no electric charge, right?
 
  • #36
VelociBlade said:
... Daschaich said that light is a wave, not a partice...

I never said that! I said if thinking about light as particles is confusing, you could make use of wave-particle duality to try thinking about it as a wave. Various equivalent approaches can be easier than others, depending on the problem.
 
  • #37
i) I leave it Daschaich to respond what he said about light beeing a wave and not a particle.

But I can tell you this: we physicsists often use the word "particle" sloppy. We mean that a particle is not a particle in the classical sense (i.e. a tiny cannon ball / sphere) but we say that a particle is a particle is particle. And this particle has properties of a wave and properties of classical particle.

ii) I did not refer to anything about electric charge or anything, I was discussing how bizarre the concept of "pure" energy is. And the guy who asked me said that he wanted energy not in the form of mass. But then I said that I wanted energy not in the form of a oscillating field.

The energy I was referring to is perhaps energy in form of photons. Colliding an antiproton with a proton will result in two photons.
 
  • #38
Daschaich: You never mentioned wave-particle duality. Also, I still don't get the part about massless particles, or how something could exist in reality as a non-kinetic wave. Could you explain this?

Malawi: What do you mean, "a particle is a particle is particle"? Also, could someone explain the posts on the first two segments of this post in terms I can understand? I'm a sophomore and I originally posted this on the classical physics forums, I had no idea the problem would involve quantum physics and the like.
 
  • #39
VelociBlade said:
Daschaich: You never mentioned wave-particle duality...

I did not use that exact phrase, but I did speak of light as being a wave, and light as being a particle. This is wave-particle duality (glossing over what the definition of "be" is).

...Also, I still don't get the part about massless particles, or how something could exist in reality as a non-kinetic wave. Could you explain this?...

What do you mean by "non-kinetic wave"? It's not a phrase I recall seeing before, and certainly not one I would use to describe something moving at the speed of light.

...Also, could someone explain the posts on the first two segments of this post in terms I can understand?...

Which posts where now?

Though quantum physics and special relativity can be difficult to learn and parse, that is the only way your question, "how can something be massless?" can be addressed.

You don't have to understand everything in the universe immediately, nor can you. Don't view this as a failure, but rather a challenge and motivation to explore those subjects more fully in coming years. Then one day someone will say "photons and gluons have no mass due to gauge invariance" and you'll reply, "yes, of course". But that day is still well off in the future, so don't worry if that imaginary conversation doesn't make any sense to you now.
 
  • #40
Look up the photoelectric effect. That will probably clear up some things for you.
 
  • #41
VelociBlade said:
Daschaich: You never mentioned wave-particle duality. Also, I still don't get the part about massless particles, or how something could exist in reality as a non-kinetic wave. Could you explain this?

Malawi: What do you mean, "a particle is a particle is particle"? Also, could someone explain the posts on the first two segments of this post in terms I can understand? I'm a sophomore and I originally posted this on the classical physics forums, I had no idea the problem would involve quantum physics and the like.

An electron is an electron.

"non-kinetic wave" what is that?, never heard of that concept..

Why does things have to have mass? I can't see the physical argument.
 
  • #42
Is spin is related to mass? Edit: just noticed W-Z bosons have mass.
 
  • #43
W,Z bosons are spin-1 and has mass

However, Weinberg-Witten theorem tells you that you can't construct a Quantum Field theory which is lorentz invariant with massless particle with spin greater than 1.
 
  • #44
malawi_glenn said:
An electron is an electron.

"non-kinetic wave" what is that?, never heard of that concept..

Why does things have to have mass? I can't see the physical argument.

Well, I guess because someone views a "thing" as a "particle" or rigid collection of particles. Of course, most "things" have inertia, of which mass is a quantitative measure.
 
  • #45
What I meant by "non-kinetic wave" was that I thought waves could only exist through kinetic energy, such as ocean surface waves, sound waves, etc. I've never really understood the concept of light waves, because of people saying it's either a wave, a particle, or both. But everything is made of something, right? After all isn't mass required for something to exist? Also, I'm trying to understand now because, with the current financial crisis in California, I might not get a chance to later.
 
  • #46
VelociBlade said:
What I meant by "non-kinetic wave" was that I thought waves could only exist through kinetic energy, such as ocean surface waves, sound waves, etc. I've never really understood the concept of light waves, because of people saying it's either a wave, a particle, or both. But everything is made of something, right? After all isn't mass required for something to exist? Also, I'm trying to understand now because, with the current financial crisis in California, I might not get a chance to later.

Well, a wave is simply a disturbance that is propagated. An elastic/mechanical wave is a disturbance that is propagated through a medium. An electromagnetic wave (any of the radiation in the EM spectrum) is a wave consisting of alternating electric and magnetic fields that are normal to each other. There is an archive to which I will post the link that should help you in your understanding of the descriptions (wave and particle) of the properties light exhibits. Don't confine your thinking of the wave-particle duality of light to comparing it to some other tangible thing in the particle sense. A wave is simply a disturbance that does carry energy.

http://www.physforum.com/index.php?showtopic=3310&st=285
 
  • #47
The energy of a wave is
E = h\nu
where the Greek letter \nu (nu) is its frequency. Shackleford mentioned the photoelectric effect, which would be a good place to learn some of this stuff.
 
  • #48
I think the the idea is no rest mass. A massless entity such as a photon cannot be brought to rest.
 
  • #49
YorkLarry said:
A massless entity such as a photon cannot be brought to rest.

This is correct, and can be a helpful way of thinking about some problems.

YorkLarry said:
I think the the idea is no rest mass.

Introducing "rest mass" as opposed to "relativistic mass" is not helpful, and tends to cause confusion and errors. There is only one mass, and massless particles have no mass. For a good discussion of this issue, I refer you to Lev Okun's article, "The Concept of Mass", which I have posted online http://daschaich.homelinux.net/okun.pdf .
 
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  • #50
VelociBlade said:
But everything is made of something, right? After all isn't mass required for something to exist?

Everything is made of something, but that something is not always matter. Mass is a property of matter, so therefore not everything must have mass. I don't claim to fully understand it either, but this is a rough version of what my physics teacher told me in high school, and it made things much clearer for me when trying to understand ideas like light.
 
  • #51
Because mass isn't fundamental. Newton thought mass was a fundamental. It was at the bottom of everything. He was wrong. There is no conservation of mass. Newton thought you could never get any more mass than what you put in.

I am reading Wilczek's book on this right now.
 

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