[hamdani yusuf (OP)]

What convinced us that photon is any more physical than phonon?

Because, unlike phonons, photons don't rely on a medium to transmit them.

We can hypothesize that light propagates in the fabric of space-time, just like gravitational wave.

[Kryptid]

We can hypothesize that light propagates in the fabric of space-time, just like gravitational wave.

Then what would make it different from a gravitational wave?

[Eternal Student]

Quote from: hamdani yusuf on Today at 12:47:17

    We can hypothesize that light propagates in the fabric of space-time, just like gravitational wave.


Then what would make it different from a gravitational wave?

   Now that's a good question:   Can we observe diffraction, refraction, reflection and interference in gravitational waves?

[hamdani yusuf (OP)]

We can hypothesize that light propagates in the fabric of space-time, just like gravitational wave.

Then what would make it different from a gravitational wave?

The objects that interact with it.
In case of gravity, it's objects with momentum.
In case of light, objects with electric charge.

[evan_au]

Then what would make (light) different from a gravitational wave?

One difference is that light is generated by an electric dipole,
- while gravitational waves are generated by a mass quadrupole.

So if you had a macroscopic (ie much bigger than atom-sized) negative charge rotating around a positive charge at 100Hz, it would generate electromagnetic waves at 100Hz.
- As I understand it, if you had a macroscopic (ie much bigger than earth-sized) positive mass rotating around another positive mass at 100Hz, it would generate gravitational waves at 200Hz.

See: https://en.wikipedia.org/wiki/Gravitational_wave#Sources

[Colin2B]

One difference is that light is generated by an electric dipole,
- while gravitational waves are generated by a mass quadrupole.

You beat me to it Evan. This difference also means that the polarisations of the light and gravitational waves are very different as is the effect on any matter they interact with.
As with all waves you would expect refraction, diffraction etc, but I would need to think what arrangements of mass would cause those in the case of gravitational waves. I suspect the effects would be small.

[Kryptid]

The objects that interact with it.
In case of gravity, it's objects with momentum.
In case of light, objects with electric charge.

And how does a wave through space-time "know" which one to interact with?

[hamdani yusuf (OP)]

The objects that interact with it.
In case of gravity, it's objects with momentum.
In case of light, objects with electric charge.

And how does a wave through space-time "know" which one to interact with?

It's still a hypothesis, which is more or less speculative, until more evidence is found. Perhaps the space-time is multidimensional, and the objects in it only interact with some of its aspects which are relevant to them.
As mentioned in the end of the video, we can interpret photons in some different ways. But interpreting them as point like particles moving through space is not very helpful.

[wolfekeeper]

Phonons are quantum mechanical phenomena, just like photons in fact.

Photons and how they interact with electrons are extremely well described in modern physics by quantum electrodynamics:

https://en.wikipedia.org/wiki/Quantum_electrodynamics

The video shows that imagining photons like extremely small particles produces more questions than answers. In many situations they behave like waves.

That's also true of electrons. That's pure Quantum Mechanics baby! That's how it works.

[hamdani yusuf (OP)]

Phonons are quantum mechanical phenomena, just like photons in fact.

Photons and how they interact with electrons are extremely well described in modern physics by quantum electrodynamics:

https://en.wikipedia.org/wiki/Quantum_electrodynamics

The video shows that imagining photons like extremely small particles produces more questions than answers. In many situations they behave like waves.

That's also true of electrons. That's pure Quantum Mechanics baby! That's how it works.

At least electron has quantified charge and mass.
What's the most convincing experiment showing that light behaves like particles and can't be explained by wave analogy?
On the other hand, what's the most convincing experiment showing that electron behaves like waves and can't be explained by particle analogy?

[evan_au]

Perhaps the space-time is multidimensional

That it is: 3 of space + 1 of time; that much is confirmed.
There are more speculative ideas about additional dimensions (eg string theory), but they have not been confirmed at this point in time.

Perhaps the space-time is multidimensional, and the objects in it only interact with some of its aspects which are relevant to them.

That is true. But the fact that light and gravity both follow an inverse-square rule to incredible accuracy at the scale of the Solar System implies that there are 3 dimensions of space (ie the density of phonons/gravitons hitting a given area reduces by a factor of 4 if you double the distance).

There are some thoughts that maybe gravity could be influenced by additional dimensions (eg string theory), and that hypothesis is being tested by measuring gravity on millimeter scales and below.

What's the most convincing experiment showing that light behaves like particles and can't be explained by wave analogy?
On the other hand, what's the most convincing experiment showing that electron behaves like waves and can't be explained by particle analogy?

They both have behaviors that act like waves, and behaviors that act like particles - that's why some people dubbed them "wavicles".
- Both electron microscopes and light microscopes have a resolution limit which depends on the energy of the particles.

[Eternal Student]

Hi.  I hope everyone is well.

@hamdani yusuf
1.   Experiments showing electrons behave like waves:  I think the double slit experiment with an electron instead of a photon emitter was previously mentioned.

2.    Going back to an earlier comment I made:   

Now that's a good question:   Can we observe diffraction, refraction, reflection and interference in gravitational waves?

   What I meant was -   this could be something for the short video you were making where diffraction and refraction were discussed.  I don't know the full answer,  I'm not sure anyone does at the moment.
 - - - - - - -

(About Gravitational Waves)...   As with all waves you would expect refraction, diffraction etc, but I would need to think what arrangements of mass would cause those in the case of gravitational waves. I suspect the effects would be small.

    This looks a lot like something you would get from the superposition of two waves.   Most waves follow a superposition principle.   Gravitational waves are unusual because the Einstein Field Equations (unlike Maxwell's equations) are non-linear, so that two separate solutions do not (in general) add to make another valid solution.
    For small oscillations (small gravitational waves) the space is assumed to be mainly empty and then the metric looks like the usual Minkowski metric plus a small perturbation.  I don't know what happens when two such waves meet, possibly the resulting perturbation is like the sum of the separate perturbations to first order approximations.

Best wishes to all.

[alancalverd]

What's the most convincing experiment showing that light behaves like particles and can't be explained by wave analogy?

Photon counting or "quantum mottle" with very low intensities of light or x-rays shows that interactions with a photodetector are individual transfers of fixed quantities of energy and momentum. Increasing intensity at a fixed wavelength/photon energy increases the rate of interactions but not the amplitude of an individual event.

On the other hand, what's the most convincing experiment showing that electron behaves like waves and can't be explained by particle analogy?

Electron diffraction patterns look just like x-ray diffraction patterns if you assign the appropriate wavelength.  In practice, neutron diffraction is easier to demonstrate but the principle is the same.


Electron-positron pair production and annihilation is fun because it demonstrates the reversibility of E = mc^2 and you end up with two 511 keV photons hurtling in exactly opposite directions, like billiard balls rather than water waves!

[hamdani yusuf (OP)]

- As I understand it, if you had a macroscopic (ie much bigger than earth-sized) positive mass rotating around another positive mass at 100Hz, it would generate gravitational waves at 200Hz.

Will the wave be sinusoid, or rectified sine wave?

[hamdani yusuf (OP)]

1.   Experiments showing electrons behave like waves:  I think the double slit experiment with an electron instead of a photon emitter was previously mentioned.

What's the material that make up the slit, i.e. blocks the motion of the electrons? Is changing the material has any effect?

[hamdani yusuf (OP)]

What's the most convincing experiment showing that light behaves like particles and can't be explained by wave analogy?

Photon counting or "quantum mottle" with very low intensities of light or x-rays shows that interactions with a photodetector are individual transfers of fixed quantities of energy and momentum. Increasing intensity at a fixed wavelength/photon energy increases the rate of interactions but not the amplitude of an individual event.

On the other hand, what's the most convincing experiment showing that electron behaves like waves and can't be explained by particle analogy?

Electron diffraction patterns look just like x-ray diffraction patterns if you assign the appropriate wavelength.  In practice, neutron diffraction is easier to demonstrate but the principle is the same.


Electron-positron pair production and annihilation is fun because it demonstrates the reversibility of E = mc^2 and you end up with two 511 keV photons hurtling in exactly opposite directions, like billiard balls rather than water waves!

Can you show some links to the research, pictures or videos showing those experiments?

[alancalverd]

Quantum mottle is part of the basic radiography syllabus. howradiologyworks.com/x-ray-cnr/ has some examples of a everyday phenomenon. It's the reason you can't increase the sensitvity of x-ray film beyond a certain limit, which is less for pediatrics than for adults, because you lose spatial resolution as the quantum noise exceeds the image contrast.

Electron diffraction is used in electron microscopy en.wikipedia.org/wiki/Electron_diffraction I used it many years ago to calibrate a small electron accelerator. Neutron diffraction has been used in crystallography particularly of organic compounds and hydrides. It's easier because neutrons have a long range in air.

Pair production and annihilation is used every day in medical imaging https://en.wikipedia.org/wiki/Positron_emission_tomography

[alancalverd]

1.   Experiments showing electrons behave like waves:  I think the double slit experiment with an electron instead of a photon emitter was previously mentioned.

What's the material that make up the slit, i.e. blocks the motion of the electrons? Is changing the material has any effect?

Best to use a conductor otherwise the blocker acquires a charge that deflects the electron beam!

[hamdani yusuf (OP)]

1.   Experiments showing electrons behave like waves:  I think the double slit experiment with an electron instead of a photon emitter was previously mentioned.

What's the material that make up the slit, i.e. blocks the motion of the electrons? Is changing the material has any effect?

Best to use a conductor otherwise the blocker acquires a charge that deflects the electron beam!

Is using a superconductor gives a better result?

[hamdani yusuf (OP)]

Quantum mottle is part of the basic radiography syllabus. howradiologyworks.com/x-ray-cnr/ has some examples of a everyday phenomenon. It's the reason you can't increase the sensitvity of x-ray film beyond a certain limit, which is less for pediatrics than for adults, because you lose spatial resolution as the quantum noise exceeds the image contrast.

Why can't it be explained using wave mechanism?

Photon detector screen reminds me of popcorn analogy to explain half life of radioactive materials.
In popcorn case, the energy is supplied more or less continuously, but the popping events occur discretely. Analogous with detector screen, we can think that the screen receive electromagnetic wave continuously, but the events of change in screen color/brightness occur discretely.