Gravitrons vs Photons: how come light and gravity exist?

[Any name will do]

TL;DR Summary

I take three physical assumptions (or logical premises): 1. matter and anti-matter annihilate each other; 1. gravitons and photons are anti-matter to each other; 3. the known universe is filled with light and gravity fields.

There is a discrepancy here.

if matter and anti-matter meet, they annihilate each other. Gravitons are anti-photons and photons are anti-gravitons. They MUST meet in immesurable quantities in our universe. Yet gravity exists, and light exists in our known universe. This denies the annihilation necessity. And annihilation necessity denies the co-existence. Something has to give. The present state of affairs leads to a logical absurdity, or to a denial of some physics theories' validity.

What is the secret to reconciling the mutually exclusive events?

 

[PeterDonis]

I take three physical assumptions (or logical premises): 1. matter and anti-matter annihilate each other; 1. gravitons and photons are anti-matter to each other; 3. the known universe is filled with light and gravity fields.

The first two of your three premises are false. So there is no issue.

 

[berkeman]

The first two of your three premises are false. So there is no issue.

You mean the "first two 1s" are false...

 

[Any name will do]

PeterDonis, two respondents clearly deny your claim. I can't accept your argument. Sorry.

For references, please see my two other forum threads. I only have three or four threads. Not hard to do, if threads can be traced by username. I am new to this site, so please forgive my ignorance on the mechanics of how to recall threads. I am a complete newbie, I can't navigate easily.

One quote from an answer to me to an earlier question:
"In the standard model, particles come in pairs. We have the electron, of course, and we must have an anti-electron (aka the positron), which has the same mass as the electron but a positive charge. Even though the positron is called "anti-matter", you could just as easily call the positron matter and the electron antimatter. The important point is that the electron and positron have a tendency to annihilate each other."

The other quote:

(They talk about photons and gravitons)

I thought their properties would be the the exact opposite

What properties would you expect to be opposite? They have no charge, no magnetic moment, etc. Pretty much the only non-zero property they have is helicity, and the helicities of particles and anti-particles is the same anyway. So the properties of a photon and anti-photon are opposites... but as the properties are equal to 0 we just get the same particle back as we started from.

I hope this answers your incredulity why I rejected your answer.

Remember, I am a complete dilettante in quantum physics and in relativity physics, but I apply logic to what I read.

According to the above, anti-particles and particles annihilate each other; and photons and gravitons are anti-particles to each other.

While I admit you may be right, I can't make that judgment. (You claimed matter and anti-matter don't annihilate each other and photons and gravitons are not each other's anti-particles). You have to duke it out :-) with the originators of the above quotes.

I also understand standard English; misplaced antecedents, or unclear relations between pronouns and their antecedents may make the descriptions inaccurate. I read what is written, I don't add or subtract, I assume that the writer writes what he means. This may be naivety on my part, yet what else can I do when I read on a topic I have zero knowledge about?

 

[PeterDonis]

two respondents clearly deny your claim

You are wrong. See below.

According to the above, anti-particles and particles annihilate each other

No. The correct statement is that if the particles are not their own antiparticles, then particles and antiparticles annihilate each other. Electrons, for example, are not their own antiparticles; positrons (anti-electrons) and electrons are distinct particles. So electrons and positrons annihilate each other. But photons are their own antiparticles, so photons do not annihilate each other.

photons and gravitons are anti-particles to each other.

This is wrong, and I don't see where anyone in the other threads you reference is saying this. Photons are their own antiparticles, and gravitons (if they exist--we have no evidence they do) are their own antiparticles, but photons and gravitons are different particles. Photons have spin 1 and gravitons have spin 2. They are not the same.

I am a complete dilettante in quantum physics and in relativity physics, but I apply logic to what I read.

That's a laudable goal, but you need to do a better job of it.

You claimed matter and anti-matter don't annihilate each other

No, I did not many any such claim. I only claimed that your statement that "matter and anti-matter annihilate each other" was false. I have explained why it is false above; note that my explanation does not say that matter and anti-matter don't annihilate each other. It says something different from either of the extremes that you incorrectly believe are the only two possibilities. In logic we call that the "false dichotomy" fallacy.

and photons and gravitons are not each other's anti-particles

Yes, I did say that, and it's correct. See above.

You have to duke it out :-) with the originators of the above quotes.

No, I don't. They already know that what I say is correct. Ask them and see.

I also understand standard English; misplaced antecedents, or unclear relations between pronouns and their antecedents may make the descriptions inaccurate. I read what is written, I don't add or subtract, I assume that the writer writes what he means. This may be naivety on my part, yet what else can I do when I read on a topic I have zero knowledge about?

All of this is irrelevant to the discussion and adds nothing of value. Please stick to what we are actually talking about.

 

[topsquark]

PeterDonis, two respondents clearly deny your claim. I can't accept your argument. Sorry.

For references, please see my two other forum threads. I only have three or four threads. Not hard to do, if threads can be traced by username. I am new to this site, so please forgive my ignorance on the mechanics of how to recall threads. I am a complete newbie, I can't navigate easily.

One quote from an answer to me to an earlier question:
"In the standard model, particles come in pairs. We have the electron, of course, and we must have an anti-electron (aka the positron), which has the same mass as the electron but a positive charge. Even though the positron is called "anti-matter", you could just as easily call the positron matter and the electron antimatter. The important point is that the electron and positron have a tendency to annihilate each other."

The other quote:

(They talk about photons and gravitons)What properties would you expect to be opposite? They have no charge, no magnetic moment, etc. Pretty much the only non-zero property they have is helicity, and the helicities of particles and anti-particles is the same anyway. So the properties of a photon and anti-photon are opposites... but as the properties are equal to 0 we just get the same particle back as we started from.

I hope this answers your incredulity why I rejected your answer.

Remember, I am a complete dilettante in quantum physics and in relativity physics, but I apply logic to what I read.

According to the above, anti-particles and particles annihilate each other; and photons and gravitons are anti-particles to each other.

While I admit you may be right, I can't make that judgment. (You claimed matter and anti-matter don't annihilate each other and photons and gravitons are not each other's anti-particles). You have to duke it out :-) with the originators of the above quotes.

I also understand standard English; misplaced antecedents, or unclear relations between pronouns and their antecedents may make the descriptions inaccurate. I read what is written, I don't add or subtract, I assume that the writer writes what he means. This may be naivety on my part, yet what else can I do when I read on a topic I have zero knowledge about?

I'm not quite sure why PeterDonis rejected 1, uhhh... your first 1. As long as you specify that particle-antiparticle pairs (ie. an electron and positron as opposed to an electron and an antiproton) annihilate then you are okay.

As to the second claim, photons and gravitons are most certainly not anti-particles. The antiparticle for the photon is a photon and the antiparticle for the graviton is a graviton. They are completely separate particles and you can quickly see this just by looking at their helicities: the photon is helicity 1 and the graviton is helicity 2.

-Dan

 

[PeterDonis]

I'm not quite sure why PeterDonis rejected 1, uhhh... your first 1. As long as you specify that particle-antiparticle pairs (ie. an electron and positron as opposed to an electron and an antiproton) annihilate then you are okay.

No, you're not. Photons are their own antiparticles, so a pair of photons is a particle-antiparticle pair, but they don't annihilate each other. That's why I phrased the correct statement the way I did in post #5. Particularly since the OP is a stickler for logic, we need to make sure we are phrasing things in a logically correct manner.

 

[Dale]

Gravitons are anti-photons and photons are anti-gravitons.

This is indeed wrong. As has been pointed out earlier.

 

[strangerep]

I don't know why this thread didn't get deleted immediately when the OP posted the crackpot assertion that "Gravitons are anti-photons and photons are anti-gravitons".

Can we close this thread now? Please?

 

[vanhees71]

No, you're not. Photons are their own antiparticles, so a pair of photons is a particle-antiparticle pair, but they don't annihilate each other. That's why I phrased the correct statement the way I did in post #5. Particularly since the OP is a stickler for logic, we need to make sure we are phrasing things in a logically correct manner.

Of course, two photons can annihilate, e.g., to an electron-positron pair. That's the reverse process of electron-positron-pair annihilation, also known as the Breit-Wheeler process. For a recent review on the issue of observation, see

https://arxiv.org/abs/2208.14943

 

[PeterDonis]

Of course, two photons can annihilate, e.g., to an electron-positron pair. That's the reverse process of electron-positron-pair annihilation

If you look at it that way, photons can "annihilate" into any particle-antiparticle pair that could in turn produce photons by annihilating each other. But if we get to that point, what we're really doing is showing that the term "annihilate" is not a good one. "Conversion" might be a better term: you have a bunch of energy that is contained in one pair of particles, and is then converted to another pair of particles.

Also, if you look at the Feynman diagrams in Fig. 1 of the paper you reference, there is always an internal line--in this case, an internal electron line between the two vertices. So the two photons that are said to "annihilate" each other never meet; each one ends on a different vertex in the diagram. The same is true for the electron and positron that are produced. And in the reverse process, the electron and positron that "annihilate" each other never meet, nor do the two photons that are produced. So the intuitive picture that the term "annihilate" suggests, that two particles meet and destroy each other, is not correct.

One would also have to consider, of course, that for the "photon annihilation" process to take place, the temperature has to be very high, whereas the electron-positron annihilation process can take place at any temperature. Similar remarks apply to other matter-antimatter annihilation processes that involve massive particles, as opposed to their reverse processes involving photons.

 

[vanhees71]

In the electron-positron annhilation to photons there's also an internal line. It's of course semantics, how you call such processes. For me annihilation is any process where two particles are going in and particles of a different kind come out.

 

[topsquark]

In the electron-positron annhilation to photons there's also an internal line. It's of course semantics, how you call such processes. For me annihilation is any process where two particles are going in and particles of a different kind come out.

When I made my comment above, I hadn't considered photon-photon "annihilation." I had always taken that to be a particle-antiparticle reaction producing two photons. Since photons can't actually do that I suppose (according to my definition, anyway) photons can't annihilate.

Something I've never checked, though, are gravitons. Is there a gg$\gamma$ vertex (or maybe a gg$\gamma \gamma$) in the gravity Lagrangian? I've never actually looked to find out, I just assumed that they could. (This is just a curiosity driven B level question.)

-Danf

 

[vanhees71]

Why do you think the Breit-Wheeler process wouldn't exist? It's very hard to verify experimentally, and this has been achieved only very recently with heavy-ion collisions and indeed not with literally "real photons".

 

[PeterDonis]

In the electron-positron annhilation to photons there's also an internal line.

Yes, I said that in my post. This is the same diagram as the Breit-Wheeler process, just flipped around in time.

 

[Vanadium 50]

Is there a gg vertex (or maybe a gg) in the gravity Lagrangian

Well, since there is no quantum theory of gravity, the answer is "maybe" or "we don't know". I suspect that such terms would cause trouble though - consider two virtual graitons interacting to produce real photons.

The term "annihilation" should probably be replaced by "interaction" in all cases. Otherwise you just get confusion. And while one can sensibly discuss antibosons,it ends not to be nearly as useful or helpful as antifermions. As a one sentence answer "a photon is its own antiparticle" is much less useful and informative as "the concept of antiparticles isn't very helpful for photons."

 

[vanhees71]

I'd say it's pretty clear what pair annihilation means, i.e., a scattering process where a particle and an antiparticle is destroyed and completely different particles occur. There are many examples. The most simple one, usually used as an exercise for tree-level QED calculations in the QFT 1 lecture is $\mathrm{e}^+ + \mathrm{e}^{-} \rightarrow \mu^+ + \mu^-$.