Yet more questions about light

[James R]

Would it confirm Bohmian Mechanics?

No.

 

[Write4U]

No.

Yes.
AFAIK, a wave function has no mass. So tell me, how could a particle be a massless wave?

Now what? Going to close this thread? That will be enlightening!

 

[exchemist]

Yes.
AFAIK, a wave function has no mass. So tell me, how could a particle be a massless wave?

Now what? Going to close this thread? That will be enlightening!

Wave functions are used to describe the quantum states of entities with mass. A wave function does not "have" a mass, as it is a description of a quantum state of an entity which has mass as one of its properties. It is the entity that has the mass, not the wave function. Photons, being massless, do not have a wave function, or not in the sense that Schrödinger developed it: https://physics.stackexchange.com/q...describes-the-wavefunction-of-a-single-photon

 

[Write4U]

Wave functions are used to describe the quantum states of entities with mass.

According to the article, photons do have mass, albeit extremely small.

A wave function does not "have" a mass, as it is a description of a quantum state of an entity which has mass as one of its properties.

But does a photon in transit not act as a wave? Is the double slit experiment not about wave interference of photons.
Hence my question about Bohmian mechanics that assumes photons to have mass, but "ride" a pilot wave that provides a "guiding equation", including wave interference and conforms to Schrodingers equation.
Trajectories of the Bohmian dynamics in the two-slit experiment.
https://www.researchgate.net/figure...iment-Each-line-corresponds-to_fig1_324435934

It is the entity that has the mass, not the wave function. Photons, being massless, do not have a wave function, or not in the sense that Schrödinger developed it: https://physics.stackexchange.com/q...describes-the-wavefunction-of-a-single-photon

I understand that, but the article claims that photons do have mass. And that makes all the difference, no?

In Bohmian mechanics a system of particles is described in part by its wave function, evolving, as usual, according to Schrödinger’s equation. However, the wave function provides only a partial description of the system. This description is completed by the specification of the actual positions of the particles. The latter evolve according to the “guiding equation”, which expresses the velocities of the particles in terms of the wave function. Thus, in Bohmian mechanics the configuration of a system of particles evolves via a deterministic motion choreographed by the wave function. In particular, when a particle is sent into a two-slit apparatus, the slit through which it passes and its location upon arrival on the photographic plate are completely determined by its initial position and wave function.

Bohmian Mechanics (Stanford Encyclopedia of Philosophy)

p.s. thanks for responding and the link.

 

[exchemist]

According to the article, photons do have mass, albeit extremely small.

Wrong. The article says the measurements show that if it has mass, it can only be less than 9.52 × 10⁻⁴⁶ kilograms. That result is consistent with the actual mass being zero, as theory indicates, as the article makes this clear.

In other words, the experiment has failed to detect any mass, with a sensitivity down to 9.52 x 10⁻⁴⁶kg

 

[James R]

Yes.

No.

AFAIK, a wave function has no mass. So tell me, how could a particle be a massless wave?

A wave function is a piece of mathematics. No piece of mathematics is a particle.

Concepts such as the mathematical construct that is called a "wave function" have no mass, because they aren't physical objects. They are concepts in your head.

A wave function is a concept that can be used to describe certain features of real-world particles. It is particularly useful for predicting the results of real-world observations made using real-world particles.

It turns out that all real-world particles behave in some ways like theoretical waves and in some ways like ideal theoretical particles, with the particular observed behaviour depending in part on the details of the particular experiment used to observe the real-world particles.

I have never claimed that any particle is a "massless wave". If somebody else made such a claim, you'd probably be better off asking them what they meant, rather than asking me.

According to the article, photons do have mass, albeit extremely small.

All the experimental evidence we have is consistent with the proposition that photons have zero rest mass. There is no reason to suspect that photons have non-zero mass, as far as I am aware.

It sounds like you probably misunderstood the article.

But does a photon in transit not act as a wave?

Nobody knows. Photons are never detected "in transit".

Theoretical descriptions of photons in transit certainly exhibit wave-like properties.

Is the double slit experiment not about wave interference of photons.

It can be about that, certainly.

The pattern of detected photons we see on the screen in the double slit experiment is consistent with the probability distribution predicted by the interference of probability waves (or electromagnetic waves, if you prefer).

Hence my question about Bohmian mechanics that assumes photons to have mass...

Does it?

I understand that, but the article claims that photons do have mass. And that makes all the difference, no?

Makes all the difference to what?

 

[Write4U]

All the experimental evidence we have is consistent with the proposition that photons have zero rest mass. There is no reason to suspect that photons have non-zero mass, as far as I am aware. It sounds like you probably misunderstood the article.

I refer back to post #100

How Heavy Can a Particle of Light Be? Scientists Just Figured It Out​

We have a new upper limit for the mass of light.

According to measurements of pulsing stars scattered throughout the Milky Way and mystery radio signals from other galaxies, a particle of light – called a photon – can be no heavier than 9.52 × 10^-46 kilograms.

It's a tiny limit, but finding that light has any mass at all would significantly impact how we interpret the Universe around us, and our understanding of physics.

However, we don't know for absolute certainty that photons are massless.

If a photon did have mass, it would need to be extremely small to not have major effects on the way the Universe appeared, which means that we just don't have the tools to measure it directly.

But we can take indirect measurements that will give us an upper limit for this hypothetical mass, and this is exactly what a group of astronomers did.

If I understand you they are not talking about anything new at all?

What a peculiar way to describe zero rest mass with an upper limit.

Perhaps they not talking about "rest" mass, but acquired mass from motion @ SOL, that cannot exceed that limit?

I could understand that.
If that upper limit was heavier than that the stated limit, it would be unable to travel @ SOL, no?

 

[Write4U]

A wave function is a concept that can be used to describe certain features of real-world particles. It is particularly useful for predicting the results of real-world observations made using real-world particles.

So are you saying there is no wave/particle duality as deduced from the double slit experiment?

The wave-particle duality of photons​

These experiments show that while a photon was detected as having the properties of a particle, interference appeared like that of a wave while simultaneously passing through the double-slit, revealing that the photon has the dual properties of a particle and a wave. More... https://photonterrace.net/en/photon/duality/#

If there is that duality, then should the wave function not equal the mass of the particle in some way, else where does any mass at all come from?

OTOH, if there is only the appearance of wave/particle duality, that would suggest Bohmian mechanics, i.e. a separate "guiding pilot wave function" that carries the particle (with an acquired mass), yet answers to the Schrodinger equation.

 

[exchemist]

I refer back to post #100

How Heavy Can a Particle of Light Be? Scientists Just Figured It Out​

If I understand you they are not talking about anything new at all?

What a peculiar way to describe zero rest mass with an upper limit.

Perhaps they not talking about "rest" mass, but acquired mass from motion @ SOL, that cannot exceed that limit?

I could understand that.
If that upper limit was heavier than that the stated limit, it would be unable to travel @ SOL, no?

Here is the actual paper: https://iopscience.iop.org/article/10.3847/1538-4357/ad2f99

They make it clear what they have succeeded in doing is setting a new, slightly lower, experimental upper bound for any mass that a photon may have.

What this means is that they have not managed to detect any evidence for mass, in spite of using an experimental technique capable of detecting any mass value greater than 9.52 x 10⁻⁴⁶kg. (This is what I explained to you in post 105, which you have ignored.)

So their experiment is a new and extreme test of current physics, which current physics has passed.

As such it does not open the way to new physics, and there is no basis in these findings for reopening non-standard ideas on the back of them.

 

[Write4U]

(This is what I explained to you in post 105, which you have ignored.)

No, I did (do) not ignore your posts. I just find it very confusing to read that a photon has no rest mass, but if it does it won't exceed that quoted number.

This the abstract from your much appreciated link.

Abstract
Exploring the concept of a massive photon has been an important area in astronomy and physics. If photons have mass, their propagation in nonvacuum space would be affected by both the nonzero mass mγ and the presence of a plasma medium.

That is what I posited. So, that's ok.
question: What about photons being affeced by the Higgs field? That's where matter acquires mass, no?

For the first time, we have derived the dispersion relation of a photon with a nonzero mass propagating in plasma.

What is meant by "deriving a dispersion relation"? Does this mean a nonzero massive photon exist or not?
If not then what "derivation" was being measured?

To reduce the impact of variations in the dispersion measure (DM), we employed the high-precision timing data to constrain the upper bound of the photon mass.

What is meant by "constraining the upper bound of the photon mass"? Again, does that mean a nonzero photon exists or not?

The dedispersed pulses from fast radio bursts (FRBs) with minimal scattering effects are also used to constrain the upper bound of photon mass.

Here it is again "upper bound of photon mass". There seemstobea lot of confirmation of nonzero massive photons.

In the future, it is essential to investigate the photon mass, as pulsar timing data are collected by PPTA and UWB receivers, or FRBs with wideband spectra are detected by UWB receivers.

It is essential to investigate the photon's mass when they have zero mass? Can a photon acquire mass?

Now we seem to have statements that we have examples of photons that do have mass under a specific circumstance ?

Am I asking the right question? If not, can anyone tell me what "in space" these folks are talking about.

I am not trying to be difficult, but this apparent contradiction intrigues me.

 

[exchemist]

No, I did (do) not ignore your posts. I just find it very confusing to read that a photon has no rest mass, but if it does it won't exceed that quoted number.

This the abstract from your much appreciated link.


That is what I posited. So, that's ok.
question: What about photons being affeced by the Higgs field? That's where matter acquires mass, no?


What is meant by "deriving a dispersion relation"? Does this mean a nonzero massive photon exist or not?
If not then what "derivation" was being measured?


What is meant by "constraining the upper bound of the photon mass"? Again, does that mean a nonzero photon exists or not?


Here it is again "upper bound of photon mass". There seemstobea lot of confirmation of nonzero massive photons.


It is essential to investigate the photon's mass when they have zero mass? Can a photon acquire mass?

Now we seem to have statements that we have examples of photons that do have mass under a specific circumstance ?

Am I asking the right question? If not, can anyone tell me what "in space" these folks are talking about.

I am not trying to be difficult, but this apparent contradiction intrigues me.

I've made it as clear as I can. If you can't understand my explanation, I can't help you any further.

 

[Pinball1970]

That is what I posited. So, that's ok.
question: What about photons being affeced by the Higgs field? That's where matter acquires mass, no?

Quarks and lepton but not neutrinos IIRC

 

[Pinball1970]

What is meant by "constraining the upper bound of the photon mass"? Again, does that mean a nonzero photon exists or not?

No it means it, "cannot be any more massive than..."

 

[Pinball1970]

Here it is again "upper bound of photon mass". There seemstobea lot of confirmation of nonzero massive photons.

No, there is no experimental evidence for a massive photon and they have just moved the finishing line closer to zero. If a photon does have some mass then it cannot be larger than 9.5 x10-45 kg that is its upper bound.

That upper bound could be reduced further if they develop new ways or refine current techniques to investigate this more accurately.

Hopefully that is all correct.

 

[DaveC426913]

It is essential to investigate the photon's mass when they have zero mass? Can a photon acquire mass?

Now we seem to have statements that we have examples of photons that do have mass under a specific circumstance ?

All our theories are built around the requirement that photons have zero rest mass. If they do not, we would have to completely rewrite our theories.

But we have yet to confirm that zero mass mass experimentally.

How do you prove a zero?
Q: To how many decimal places does it have to be zero before it's zero? A: Infinitely many zeros.

So far, we have shown the rest mass of a photon to be as near to zero as 0.000 000 000 000 000 000 000 000 000 000 000 000 000 000 01kg

When we test for the mess of a photon, we can only do so to a certain degree of precision. If we can't test smaller than that, then someone could always come along and say "it's got mass, just less than you were able to measure".

So we keep testing to push that observed number down - to fifty decimal places, then sixty (note that each decimal place is ten times greater precision. So 10^-50 is 10,000 times more precise than our current observation, 10^-60 is a hundred million trillion more precise than that). We will never reach infinity.

Still, we're "pretty sure" it's zero, Since if it were not, most of our 21st century civilization would collapse around our ears.

 

[exchemist]

All our theories are built around the requirement that photons have zero rest mass. If they do not, we would have to completely rewrite our theories.

But we have yet to confirm that zero mass mass experimentally.

How do you prove a zero?
Q: To how many decimal places does it have to be zero before it's zero? A: Infinitely many zeros.

So far, we have shown the rest mass of a photon to be as near to zero as 0.000 000 000 000 000 000 000 000 000 000 000 000 000 000 01kg

When we test for the mess of a photon, we can only do so to a certain degree of precision. If we can't test smaller than that, then someone could always come along and say "it's got mass, just less than you were able to measure".

So we keep testing to push that observed number down - to fifty decimal places, then sixty (note that each decimal place is ten times greater precision. So 10^-50 is 10,000 times more precise than our current observation, 10^-60 is a hundred million trillion more precise than that). We will never reach infinity.

Still, we're "pretty sure" it's zero, Since if it were not, most of our 21st century civilization would collapse around our ears.

Good effort. Let’s see if the penny drops.

 

[Write4U]

So we keep testing to push that observed number down - to fifty decimal places, then sixty (note that each decimal place is ten times greater precision. So 10^-50 is 10,000 times more precise than our current observation, 10^-60 is a hundred million trillion more precise than that). We will never reach infinity.

Still, we're "pretty sure" it's zero, Since if it were not, most of our 21st century civilization would collapse around our ears.

Ok, I understand that, even as at first glance it appears to be conraditory .

From a prior paper showing "lower limits" than the current paper with the newly established "higher limit" .

What is the mass of a photon?​

This question falls into two parts:

a) Does the photon have mass? After all, it has energy and energy is equivalent to mass.

b) Photons are traditionally said to be massless. This is a figure of speech that physicists use to describe something about how a photon's particle-like properties are described by the language of special relativity.

It is almost certainly impossible to do any experiment that would establish the photon rest mass to be exactly zero. The best we can hope to do is place limits on it. A non-zero rest mass would introduce a small damping factor in the inverse square Coulomb law of electrostatic forces. That means the electrostatic force would be weaker over very large distances.

The Charge Composition Explorer spacecraft was used to derive an upper limit of 6 × 10−16 eV with high certainty. This was slightly improved in 1998 by Roderic Lakes in a laboratory experiment that looked for anomalous forces on a Cavendish balance. The new limit is 7 × 10−17 eV. Studies of galactic magnetic fields suggest a much better limit of less than 3 × 10−27 eV, but there is some doubt about the validity of this method.

What is the mass of a photon?

 

[exchemist]

Ok, I understand that, even as at first glance it appears to be conraditory .

From a prior paper showing "lower limits" than the current paper with the newly established "higher limit" .

What is the mass of a photon?​

This question falls into two parts:

a) Does the photon have mass? After all, it has energy and energy is equivalent to mass.

b) Photons are traditionally said to be massless. This is a figure of speech that physicists use to describe something about how a photon's particle-like properties are described by the language of special relativity.

What is the mass of a photon?

zero.

 

[DaveC426913]

Ok, I understand that, even as at first glance it appears to be conraditory .

How does it appear to contradictory?

Look: I have a Tim Horton's Gift Card. I am certain there's no money left on it. That's my theory.

But I can't be sure unless I experiment.

So I go to Timmie's and I try to buy $25 worth of donuts on it. It gets declined as insufficient funds.
So I try to buy $10 worth of donuts with it. It gets declined as insufficient funds.
So I try to buy $1 worth of donuts with it. It gets declined as insufficient funds.

(Notice that my experiments never tell me what the value is, all they can do is tell me if it falls above the value I am testing for.)

So I have now constrained the upper limit of funds on the card to less than $1.

And I have reached the current limit of my ability to experiment. I can't try an amount less than that right now because Timmie's doesn't have any products that cost less than $1 (although they might have specials in the future, so I will try again later when that becomes available).

Now here is question for you:

Is there anything about my experiments and their results that leads you to conclude that my card has any money on it at all?

No. My theory - that it has no money on it - still holds. The practical upshot of this is that I am going to go hungry today.

And my theory will continue to hold until I can manage to figure out how to buy a product for all the way down to $0 (which is never gonna happen).

Experimentally, I can never prove that the card has zero dollars on it; the best I can do is constrain its upper limit. Still, the card almost surely does have $0 on it. And that means I'm going to go hungry - and that the world won't come crashing down around my ears.

 

[James R]

If I understand you they are not talking about anything new at all?

The experiment put a new upper limit on the mass of the photon. That's new.

What a peculiar way to describe zero rest mass with an upper limit.

It's quite standard in science to quote values with uncertainties.

In this case, the experiment found that the mass of the photon lies in the range $$0\le m<9.52\times 10^{-46}\text{ kg}$$
To put it another way, it might have a mass of zero, or it might have a mass of
0.000000000000000000000000000000000000000000000952 kg, or any value in between zero and that number.

Since we have good theoretical reasons for suspecting that the actual mass of the photon is zero, and this experimental result is entirely consistent with that expectation, the only "news" here is that we've further narrowed down the range of possibilities if it turns out that we were wrong all along about the idea that the photon has no mass.

Perhaps they not talking about "rest" mass, but acquired mass from motion @ SOL, that cannot exceed that limit?

They are talking about rest mass. Note, however, that if the mass of the photon is actually zero, then it can never be brought to rest; if, on the other hand, it does have a minuscule mass, then it would be theoretically possible to bring it to rest.

Just so you know: nobody has ever observed a photon at rest.

If that upper limit was heavier than that the stated limit, it would be unable to travel @ SOL, no?

Correct, though it would still travel very close to the speed of light after being given the tiniest push.

So are you saying there is no wave/particle duality as deduced from the double slit experiment?

In my previous reply to you, I wrote:

It turns out that all real-world particles behave in some ways like theoretical waves and in some ways like ideal theoretical particles, with the particular observed behaviour depending in part on the details of the particular experiment used to observe the real-world particles.​

That is a description of wave/particle duality.

So, no, I'm not saying there is no wave/particle duality.

If there is that duality, then should the wave function not equal the mass of the particle in some way, else where does any mass at all come from?

Our current best theory says that mass comes from the way that excitations in certain quantum fields interact with another field (the Higgs field).

OTOH, if there is only the appearance of wave/particle duality, that would suggest Bohmian mechanics, i.e. a separate "guiding pilot wave function" that carries the particle (with an acquired mass), yet answers to the Schrodinger equation.

Bohm's theory is designed to predict all the same experimental results as regular quantum mechanics. Only the suggested "mechanism" is different.

I'm not aware of any proposed experimental investigation that could distinguish Bohmian physics from regular old Copenhagen quantum mechanics. Are you?

What is meant by "constraining the upper bound of the photon mass"?

It means doing an experiment that will give one result if the mass is larger than a certain value and a different result if the mass is larger than that value. The result, in the case of the experiment under discussion, is that the photon mass was found to be less than the quoted value that was calculated based on the parameters of the particular experiment. Hence, the experiment puts an upper bound on the photon mass.

The experiment determined that, if the photon has non-zero mass, then that mass must be less than a particular value. The experiment rules out the possibility that the photon mass is larger than that value. Hence, the value is an "upper bound".

To give you another example, without knowing anything about your mass, I can confidently put an upper bound on it. I will happily assert, for instance, that your mass is not greater than 500 kilograms. If I had to guess, I'd say that, according to my current hypothesis, your mass is not greater than 120 kilograms, but I could be wrong about that. So, my current upper bound, based only on general knowledge about typical human body masses, is 500 kg, for your mass. New information - or an experimental measurement - could reduce that upper bound to 120 kilograms or less. Nevertheless, I can confidently say that your mass is in the range $$0<m<500\text{ kg}$$. In fact, I can do better, because in this case I'll also hypothesise a lower bound that is greater than zero, based on my repeated observation that humans seem to all have non-zero mass. So let's hypothesise that your mass is $$50 kg<m<120\text{ kg}$$I could certainly test that hypothesis and lower the uncertainty limits, in principle.

Do you understand the ideas of upper and lower bounds now?

There seems to be a lot of confirmation of nonzero massive photons.

There is no confirmation that any photons have had, or ever will have, any mass other than zero.

It would be wrong of me to claim that there seems to be a lot of confirmation that your mass is 85 kg, when all I have is a lower bound of 50 kg and an upper bound of 500 kg. You see why?

It is essential to investigate the photon's mass when they have zero mass?

We don't know that they have zero mass. All we have is a lower and an upper bound on the mass. The only way to be sure is to investigate.

Can a photon acquire mass?

I'm aware of no theory that predicts that photons ought to have non-zero mass. There might be one, but it would have to be incompatible with a lot of other well-verified theories. Still, some of our well-established theories have turned out to be wrong before. There's no way to know without investigating.

Now we seem to have statements that we have examples of photons that do have mass under a specific circumstance ?

No, we don't.