Experiment on mass of a photon

[Slait]

Ive been trying to find if anyone has done a simple experiment to test relativistic mass of a photon. I was hoping if anyone has found documentation or results of the following experiment:

In a vacuum fire a stream of photons at different frequencies at a pressure plate and measure the pressure exerted on the plate from the photons. Also if the same experiment was done with a reflective pressure plate for a different result.

So far i haven't found anything with google, but it seems like a simple experiment that someone out there has tried.

 

[sophiecentaur]

That experiment would show the Momentum of photons and has been done, in various forms, many times.
Simply finding momentum will not tell you mass.

 

[Dale]

See: http://www.edu-observatory.org/physics-faq/Relativity/SR/experiments.html

 

[sophiecentaur]

See: http://www.edu-observatory.org/physics-faq/Relativity/SR/experiments.html

"As of July 2007, their reported (upper) limit on the photon mass is 6×10−17 eV/c²"
Pretty small,huh? Compared with about 5.5e-11 eV/c² for the electron. This limit has decreased by a factor of about a hundred over the last twenty years or so. It is still falling fast . . . .

 

[bcrowell]

Goldhaber and Nieto, "Terrestrial and Extraterrestrial Limits on The Photon Mass," Rev. Mod. Phys. 43 (1971) 277–296

R.S. Lakes, "Experimental limits on the photon mass and cosmic magnetic vector potential", Physical Review Letters , 1998, 80, 1826-1829, http://silver.neep.wisc.edu/~lakes/mu.html

Luo et al., “New Experimental Limit on the Photon Rest Mass with a Rotating Torsion Balance”, Phys. Rev. Lett, 90, no. 8, 081801 (2003)

The tighter limits are model-dependent.

 

[mfb]

Compared with about 5.5e-11 eV/c² for the electron.

I think you meant 5.11e5 here.

The http://pdglive.lbl.gov/popupblockdata.brl?nodein=S000M&inscript=Y&fsizein=1 has a large collection of photon mass measurements. The best limits come from astronomy, but there are lab experiments as well.

 

[sophiecentaur]

The mass is about 5.5MeV. When you divide this by csquared, don't you get the same answer as I did? I was only using(trying to use) the same units as were used in that quote - I wouldn't have done that voluntarily in a million years. Did I get my sum wrong?
Less than one millionth of the mass of an electron for the upper limit for the mass of a photon seemed ok to me and pretty damn near zero.

 

[mfb]

The mass of an electron is 511keV in a unit system where c=1. If you want to use SI-units, the mass is 511keV/c^2.
The neutrino mass searches are at a precision of roughly 1 eV now, and the (model-independent) upper limit on the photon mass is ~10^-24 times the electron mass.

 

[sophiecentaur]

Thanks - the units in that first reference confused me. The situation is way more extreme then.

 

[Dale]

The mass is about 5.5MeV. When you divide this by csquared, don't you get the same answer as I did? I was only using(trying to use) the same units as were used in that quote - I wouldn't have done that voluntarily in a million years. Did I get my sum wrong?
Less than one millionth of the mass of an electron for the upper limit for the mass of a photon seemed ok to me and pretty damn near zero.

Hi sophiecentaur, the units are a little weird, but it is a common unit in particle physics. The eV is a unit of energy (1.6E-19 J), and by E=mc² you can have a unit of mass which is eV/c². The eV/c² is already a unit of mass, so you don't need to manually divide by (299792458 m/s)² to get the mass. So an electron has a rest-energy of 511 keV and therefore a mass of 511 keV/c².

So a 6E-17 eV/c² limit is not just one millionth of the mass of an electron, but closer to 1E-22, or a ten-billion-trillionth of the mass of an electron. At a certain point, numbers just become unfathomable. To put it in scale, that is approximately the mass ratio between a typical human and mars. And that isn't the tightest limit on the mass of the photon.

 

[sophiecentaur]

To put it in scale, that is approximately the mass ratio between a typical human and mars.

Is you sayin I is fat?

 

[Slait]

the only one that sounds like it might be close to what I am talking about is the most recent experiment but i don't know how to access the documents for the details. The reason I'm searching is I'm skeptical about light having mass. I want to see an experiment of light actually pushing a physical object. All the other experiments seems like a math calc using the observed energy and not the effect on other matter

 

[sophiecentaur]

the only one that sounds like it might be close to what I am talking about is the most recent experiment but i don't know how to access the documents for the details. The reason I'm searching is I'm skeptical about light having mass. I want to see an experiment of light actually pushing a physical object. All the other experiments seems like a math calc using the observed energy and not the effect on other matter

I think you are still missing the point that it is the Momentum of the light that does the 'pushing' (hundreds of examples of this, all over the place). The momentum of a photon does not involve the photon having mass. Indeed,a very 'simple' outcome of Maxwell's equations, applied to waves, predicts light pressure (the correct amount) without involving the use of photons at all. Any advanced EM book will show how this is done.

 

[DrGreg]

See our FAQ: https://www.physicsforums.com/showthread.php?t=511175

 

[bcrowell]

See our FAQ: https://www.physicsforums.com/showthread.php?t=511175

The FAQ doesn't address the question of how we know that the rest mass of the photon is zero (or smaller than some empirical upper bound).

 

[Slait]

I think you are still missing the point that it is the Momentum of the light that does the 'pushing' (hundreds of examples of this, all over the place).

Ok, sorry, momentum without mass...i think something is wrong there. Anyway you mentioned hundreds of examples, do you have a link to any of those examples? because that's what I'm looking for

 

[Dale]

Ok, sorry, momentum without mass...i think something is wrong there.

No, nothing is wrong. Energy, mass, and momentum are related as follows: c^2 m^2 = E^2/c^2 - p^2. For p=0 that reduces to the familiar E=mc², and for m=0 it reduces to E=pc.

 

[Slait]

Again, that equation is based on the energy. I want to see light pushing an object. I don't believe that it can. Science isn't a religion, something isn't true just because a book says so.

The only thing that interferes with my learning is my education. -Albert Einstein

 

[ZapperZ]

Again, that equation is based on the energy. I want to see light pushing an object. I don't believe that it can. Science isn't a religion, something isn't true just because a book says so.

The only thing that interferes with my learning is my education. -Albert Einstein

So you don't buy into (i) Compton scattering (ii) the RF structures that are used in many particle accelerators to accelerate particles?

Zz.

 

[Mentz114]

Again, that equation is based on the energy. I want to see light pushing an object. I don't believe that it can. Science isn't a religion, something isn't true just because a book says so.

The only thing that interferes with my learning is my education. -Albert Einstein

Einstein demonstrated in a 1917 paper that 'light quanta' exchange momentum with atoms when emitted or absorbed. This exchange of momentum is used to slow down bosons to cool them. This experiment won a Nobel prize for the physicists involved.
http://www.nobelprize.org/nobel_prizes/physics/laureates/1997/illpres/index.html and http://physics.aps.org/story/v21/st11

Einstein's 1917 paper is called "On the Quantum Theory of Radiation", Physik, Z. 18, p 121

 

[Slait]

Einstein demonstrated in a 1917 paper that 'light quanta' exchange momentum with atoms when emitted or absorbed. This exchange of momentum is used to slow down bosons to cool them. This experiment won a Nobel prize for the physicists involved.
http://www.nobelprize.org/nobel_prizes/physics/laureates/1997/illpres/index.html and http://physics.aps.org/story/v21/st11

Einstein's 1917 paper is called "On the Quantum Theory of Radiation", Physik, Z. 18, p 121

Now we are getting somewhere. That experiment is close but the laser isn't moving the matter, its just vibrating the field in a resonant frequency to reduce the vibration of the atoms.

 

[ZapperZ]

Now we are getting somewhere. That experiment is close but the laser isn't moving the matter, its just vibrating the field in a resonant frequency to reduce the vibration of the atoms.

{ZapperZ taps his fingers and points to the two examples he mentioned.}

Zz.

 

[Slait]

{ZapperZ taps his fingers and points to the two examples he mentioned.}

Zz.

Only 1 example. The experiment was based on Einsteins theory

 

[ZapperZ]

Only 1 example. The experiment was based on Einsteins theory

You are purposely being evasive.

Which one are you referring to? Besides, it only takes ONE to falsify your idea. The hundreds of particle accelerators around the world using RF structures clearly show that EM radiation CAN "push" on matter. So look who is being "religious" here?

Zz.

 

[Dale]

Again, that equation is based on the energy. I want to see light pushing an object.

That equation tells you exactly how much of a push to expect for a given amount of energy, and it also tells you that mass is not required for something to have momentum. The point is that the equation is a direct rebuttal to your suggestion that there was anything wrong with something having momentum but not mass.

Here is a bit of history on the early experiments to measure radiation pressure, 110 years ago:
http://www.dartmouth.edu/~pressureoflight/history/history2.html

Compton received the Nobel Prize in 1927 for demonstrating that photons have momentum:
http://prola.aps.org/abstract/PR/v21/i5/p483_1

Here is a freshman-level modern experiment:
http://www.gamma.nbi.dk/Galleri/gamma152/christopherrjacobsen.pdf

I don't believe that it can. Science isn't a religion, something isn't true just because a book says so.

This makes you sound very immature and a little rude. The equations that we use have been experimentally tested and confirmed over and over. The particular thing you are worried about has been well-known for more than a century and can be tested by freshman physics students.

 

[Mentz114]

Now we are getting somewhere. That experiment is close but the laser isn't moving the matter, its just vibrating the field in a resonant frequency to reduce the vibration of the atoms.

No. The photons exchange momentum with the atoms. The tuning of the laser field makes it more likely for an atom to absorb when moving. Each absorption slows the movement.
The experimental evidence is undeniable, so stop denying it.

 

[Slait]

The torsion experiments are good. But there are two variables that i can't help but wonder.
1: Its being pushed by they residual air. Its very hard to make a perfect vacuum or even prove that its a perfect vacuum. Crookes radiometer has to be in a partial vacuum to work
2: The torsion pendulum is just bending from the light heating it.
They are possibilities.

As for the Compton scattering its hard to know what's actually happening at the sub atomic level. The electron can be knocked off by the electromagnetic field vibrating it away much like an explosion from heat.

My reasoning for doubting is because the electrons creating the wave vibrate perpendicular to the velocity of the wave. So wouldn't it make sense that the energy is perpendicular to the wave, and the wave traveling through space is just the transfer of the energy?

I really would like to see something move using just electromagnetic energy

 

[WannabeNewton]

This is a ridiculous and immature rejection of the experiments and conclusions. At this point all I see is a random stringing together of words that don't make any physical sense in an attempt to deny the currently accepted fact that photons carry momentum e.g. "energy is perpendicular to the wave". In fact, an electromagnetic field carries momentum too.

 

[Slait]

This is a ridiculous and immature rejection of the experiments and conclusions. At this point all I see is a random stringing together of words that don't make any physical sense in an attempt to deny the currently accepted fact that photons carry momentum e.g. "energy is perpendicular to the wave". In fact, an electromagnetic field carries momentum too.

Everyone that sails too far west disappears, conclusion, the Earth is definitely flat. Cant argue with that logic

 

[PAllen]

Everyone that sails too far west disappears, conclusion, the Earth is definitely flat. Cant argue with that logic

Just to be clear what you reject:

- Newton's corpuscular theory of light (it proposed momentum for light)
- Maxwell's Equations make a precise quantitative prediction for light momentum that is
considered confirmed in 1901 by the Nichols Radiometer (not Crookes).
- Relatavistic kinematics
' - Quantum theory esp. QED

 

[WannabeNewton]

Everyone that sails too far west disappears, conclusion, the Earth is definitely flat. Cant argue with that logic

What does this even have to do with your rejection of VERIFIED science? The best I can do is tell you to take a look at a quantum mechanics textbook that discusses the mathematics behind the Compton Scattering. See, for example, Zettili's quantum mechanics book section 1.2.3.

 

[PAllen]

Yet another confirmation of the totally non-controversial fact of light having momentum:

http://www.ucl.ac.uk/opticon1826/archive/issue7/ResearchNotes/RNotes_Engin_Jones_PowerofLight.pdf

 

[sophiecentaur]

Again, that equation is based on the energy. I want to see light pushing an object. I don't believe that it can. Science isn't a religion, something isn't true just because a book says so.

The only thing that interferes with my learning is my education. -Albert Einstein

I should say that it is your approach that it the 'religious' one, actually. You 'feel' something should be true yet you reject any evidence for the opposite view by just shifting your ground as new evidence is presented to you.
What is written in Science books (unlike religious texts) is the result of sufficient body of opinion and evidence and has evolved more than a little since Science books were first written. Text books are the effect and not the cause.

You want examples of 'light pushing things'? There are literally billions of photos of nuclear 'events' that indicate strongly that the principle of conservation of momentum is valid (by their self-consistency) and those recorded events involve taking the momentum of photons into account.

Just because those events don't happen to involve things on a scale of a torch pushing a tin can along the road doesn't invalidate the principle.

Also, if the pressure of light on satellites were not taken into account, they would be in the wrong places and with the wrong orientation.

You appear not to want to see these examples as confirmation of your erroneous view. Open your mind to a different interpretation from the one you have at present. Consider that Momentum may not always correspond to mv.

 

[ZapperZ]

You can only lead a horse to water. You cannot make it drink, even when you shove the water into its face.

This thread is done.

Zz.