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a reply to: Arbitrageur

Great post and bang on the numbers (as always!!) Just to add a little note here for others who are essentially claiming single photons do not exist

www.picoquant.com...

This is a note about time-correlated single photon counting, in essence it is a technique that allows you to extract the timing properties of a process that either produces light or produces secondary light (such as scintillation or fluorescence)

It kind of works as follows,
1) You filter a light source down to the single photon level
2) You set time=0s when the light source fires, if using a LED pulser or Laser pulse this is a simple logic signal.
3) You count the time between the emission, and detection, if there is no detection, you reset and start again.
4) You plot a histogram of time of arrival

The reason why this is something very interesting to do is because often you can identify various light sensitive chemicals in life science areas due to fluorescence light when exited by incoming photons. Alternatively it can be used to characterize the timing signature of a light source independent of the detector timing characteristics.

I used this personally in order to characterize several LED pulsers in order to de-convolve the source timing signature from the pulse shape produced by my detector (when using high intensity LED flashes)


I used a PMT and also an APD to do it. PMTs are devices that work essentially only because of the photo-electic effect. They are basically vacuum bulbs coated on the inside with a 100-200nm thick layer of extremely low work function material.

There is a wonderful page on the subject located here
www.hamamatsu.com...

You basically absorb the energy of a photon above the work function, and kick off an electron. It then has a chance of being accelerated through the PMT and giving a signal. The gain of a PMT is very stable and will give you a very clean peak corresponding to 1 photon detection... we call this photo-electrons since that is what we see with the device, rather than photons themselves. They unfortunately don't produce a binary like 1 2 3 4 5 count of photons that are detected, typically a well setup pmt for photon counting might give you the 2nd or 3rd peak, but after that it becomes kind of smeared into one in a rough Poisson distribution.

a reply to: Arbitrageur

thank you. Sorry I did not look up a link you gave me but the fact that you copied and pasted text instead of writing it makes me feel a little easier.

Double slit experiment and as a result 'wave-particle' duality of photon is something I don't think is complete (satisfactory) explanation.


thanks again.

a reply to: ErosA433

Photons do exist, no doubt. Only photon in classical interpretation is a quanta of energy or a packet of energy which according to this definition is a wave, a short pulse of isolated energy quanta that does not mean it is a particle.

The fact that we see dots on detector screen during double slit test still imo can be explained leaving wave nature of photon as the only correct assumption.

Not only me but lots of folks are not happy with duality. With that said I am trying to decide for myself what quanta of energy is in terms whether it is a wave or a particle. It cannot be both at the same time.

I look at photon as an event, instance of releasing or absorbing quanta of energy.
Say, we build a detector dish that is only one atom deep (thick). Atoms arranged side by side forming wide area of detector.
Photon released from photon gun, imo, will start to spread itself along hypothetical surface of the sphere that is photon wave length deep. Since it is still quanta of energy, only thinned out, it is going to have all characteristics of initial pulse no matter how far it travels to detector.

Upon reaching my detector which is only one atom thick, first atom that encounters wave front will absorb entire wave because it absorbs energy in quanta, not half quanta and not one and half quanta.
This way entire wave will collapse to an instance of absorption. Neighboring atoms in our dish array will get nothing.

Now lets send second isolated pulse of energy (second photon). Since first atom in my detector has already absorbed first packet and cannot absorb more, then neighboring atom gets to absorb second incoming quanta. The wave as the whole quanta (no matter how thinned out) is consumed once more leaving other neighboring atoms untouched.

As I send one by one more single shots of quanta (photon) more and more atoms, again one by one, will absorb them. The absorption will look on my detector screen with center area as the beginning point, where 'dots' arrive first and then slowly spreading outward forming typical wave pattern on it with fewer dots toward detector edge since atoms closer to the and starting from the center already been fed and not taking any more. All they do is getting hotter each time energy quanta hit them (the spark and the 'dot' seen only when absorbed) before absorbed by the atoms that are further from the center.

If I keep shooting photons the entire detector dish will look uniformly dark and very hot.

With what I said above, solves two moments for me. First collapse of wave mechanism (wave quanta can only be absorbed by one atom at the time), second confirming that photon is a wave and dots do not represent particle nature of it.

something like that.

))

originally posted by: greenreflections
The wave as the whole quanta (no matter how thinned out) is consumed once more leaving other neighboring atoms untouched....

photon is a wave and dots do not represent particle nature of it.

I think about 90% or more of the population is confused by the way physicists use the term "particle". Mass media demonstrations showing marbles fired through a double slit as examples of particles are part of the reason.

But once you get past this confusion, you will realize the self contradiction in your post, because you're talking about the quanta and saying they are not particles....the quanta ARE the particles so if you believe in the quanta you believe in particles. Photons are definitely not like little marbles and physicists who say they have "particle-like" behavior don't think they are. So you're like most people and simply don't understand what physicists mean by the word "particle".

Look at a physicist's description of the photon and it's not much different from yours aside from your understanding of what "particle" means, in fact he doesn't even call it a "particle" in this description, he calls it "particle-like":

abyss.uoregon.edu...

Quantum, in physics, discrete natural unit, or packet, of energy, charge, angular momentum, or other physical property. Light, for example, appearing in some respects as a continuous electromagnetic wave, on the submicroscopic level is emitted and absorbed in discrete amounts, or quanta; and for light of a given wavelength, the magnitude of all the quanta emitted or absorbed is the same in both energy and momentum. These particle-like packets of light are called photons

So it sounds to me like you and the physicist who wrote that are saying the same thing except when you say "dots do not represent particle nature of it." it appears that you're using the word particle differently because the rest of your post says there are quanta of electromagnetic radiation...those ARE the "particles" so if you believe in quanta you believe in particles! If you say otherwise you don't understand the terminology.

originally posted by: ErosA433

Thanks for adding some details about photons. I can see why people accuse virtual photons of being mathematical constructs, but I can't understand how someone would say regular photons are mathematical constructs unless they're not familiar with photon experiments.

The reason why this is something very interesting to do is because often you can identify various light sensitive chemicals in life science areas due to fluorescence light when exited by incoming photons. Alternatively it can be used to characterize the timing signature of a light source independent of the detector timing characteristics.

It's easy to understand how a timing experiment such as you describe does what that second sentence describes, but I'm not quite sure about the first sentence, is it to look at the timing properties of the fluorescence and do those vary that much?

They unfortunately don't produce a binary like 1 2 3 4 5 count of photons that are detected, typically a well setup pmt for photon counting might give you the 2nd or 3rd peak, but after that it becomes kind of smeared into one in a rough Poisson distribution.

Are you saying that's what happens if the photons don't have enough separation from each other in time? The detections get smeared together? I don't know if you watched the video on single photon interference, it's not as impressive as the videos I've seen on single electron interference, but Derek Muller was using a PMT and had a counter attached to it. Here's the link again if you get a chance to see it: www.youtube.com...

He said one of the reasons his counter wasn't perfectly accurate was because it was getting background detections in the PMT from cosmic rays even when his light source was turned off (which is related to the reason your dark matter experiment is conducted underground I guess). But aside from the background with the light source off, he didn't show how fast the counter was counting during the experiment so I don't know if the "smearing" you mentioned was a problem for his counter.

I also wondered why the single-photon experiment didn't do so well on the dark bands, which weren't so dark. Here's a picture of the dark bands from the full laser source, which as you can see are pretty dark:



He showed this graph where the intensity goes to zero in the dark bands and since they're rather dark perhaps it very nearly does go to zero:


Now look at the "single photon" graph where the photon count goes nowhere near zero in the "dark" or not really so dark bands, I'd call them lower intensity areas:



So according to his explanation part of the reason the dark bands aren't so dark is from cosmic rays, in which case he'd get darker dark bands doing the experiment in an underground lab. But I suspect he must have other sources of error too for the "dark bands" to have that much intensity.

a reply to: Arbitrageur

Timing properties of optical processes are very important and are used in identifying certain chemicals. All it means is lets say you have two chemicals, chemical A has an excited atomic state, that decays in 5ns, and chemical B an exited atomic state that decays in 10 ns

These decays to the ground state release a single photon.

You excite the states in the first place via photons, to be precise UV photons lets say.

If your detector has a long recovery time, and your signal will first have a sharp rise going from 20% to 80% signal size in 2.5ns, and then a slower decay back to the baseline which requires 10 ns, you have a signal width of around 12.5 ns

So if you used a high intensity UV LED flash, your signal will likely look identical for both of these chemicals. So how do we tell them apart? That method is this time correlated single photon experiment.

By hitting the sample one photon at a time, it allows you to build up a histogram with time on the x axis and time correlated counts on the Y axis. It will in effect be not limited by the rise time or pulse shape produced by the Detector, and only on the time profile of the process under examination.


On the PMT pulse thing smearing out, it is mostly caused by the charge width of the single photo electron in a device but also the amplification chain smearing the signals. A PMT accelerates electrons into metallic plates, when they impact, the plates release more electrons, and we cascade till we eventually see a gain of 10^5 to 10^7 depending on what voltage you apply.

So if you look at a PMT exposed to a single photon source, you will see a spectrum with a pedistal (this is the noise peak when the pmt is not triggered by the photon) and then a single photo-electron, and then a lesser order 2 or 3 photoelectrons, (a light source filtered down to the single photon level can still produce multiple photons)

The first peak experiences gain oise, but only from the second peak. The second peak experiences noise from both the 1st and 3rd... the 3rd, from the 1st, 2nd and 4th... and so on... so the peak widths basically become wider and it smears out.

That said, statistically, you can still look at a specturm like this, and as long as the 1st photo electron peak is resolved, you can say exactly how much light you see on average from the source per pulse.


Sounds complicated but its not as bad as it sounds

originally posted by: Arbitrageur
He said one of the reasons his counter wasn't perfectly accurate was because it was getting background detections in the PMT from cosmic rays even when his light source was turned off (which is related to the reason your dark matter experiment is conducted underground I guess). But aside from the background with the light source off, he didn't show how fast the counter was counting during the experiment so I don't know if the "smearing" you mentioned was a problem for his counter.

Yep, saw the video, the issue with PMTs (and indeed any detector) is that they are effected by noise, in the case of a PMT the workfunction of the active material deposited on the front face is so low that you get thermal boil off of the electrons. This is so called dark noise because it gives you a constant rate of single photo-electron pulses due to the PMT just being turned on...

This said there are ways of getting around it such as using a tagged source, (only using the pmt signal for a very short period centered around a trigger point (like a laser fire) and only integrating for a short period of time), cooling the detector and dark adapting the PMT (bit like cooling but its basically allowing the PMT to sit in the dark long enough so the heating of the photocathode from infrared is allowed to dissipate.

originally posted by: ErosA433
By hitting the sample one photon at a time, it allows you to build up a histogram with time on the x axis and time correlated counts on the Y axis. It will in effect be not limited by the rise time or pulse shape produced by the Detector, and only on the time profile of the process under examination.

Thanks for the explanation, I learn something every day and didn't know about this application.

originally posted by: ErosA433
Yep, saw the video, the issue with PMTs (and indeed any detector) is that they are effected by noise, in the case of a PMT the workfunction of the active material deposited on the front face is so low that you get thermal boil off of the electrons. This is so called dark noise because it gives you a constant rate of single photo-electron pulses due to the PMT just being turned on...

I thought that seemed like a lot of background for cosmic rays, so maybe there's some thermal boil-off in that background too. Maybe even more photons from that than from cosmic rays? Now I start to get a more accurate picture of why the experiment worked like it did.

It is likely both, cosmic rays have a very high rate on surface, but, the typical dark noise rather of a PMT can be in the 5-20KHz range depending on a PMT and how light tight the box is.

So if you have an integration window of say 1x10^-6 seconds, and the rate of dark counts in the PMT is 10kHz, that is on average 1 pe every 1x10^-4... thus... your the samples you take of your detector will on average contain 0.01 thermal photons... SOOOooo As you increase the samples, your single pe being included with the real signal will go up with it.

Cosmics - depending on energy can be 1kHz per square meter...

So it will be a combination of all of it... that said, the experiment can be improved by using a Muon veto detector.

originally posted by: greenreflections
a reply to: ErosA433

Photons do exist, no doubt. Only photon in classical interpretation is a quanta of energy or a packet of energy which according to this definition is a wave, a short pulse of isolated energy quanta that does not mean it is a particle.

The fact that we see dots on detector screen during double slit test still imo can be explained leaving wave nature of photon as the only correct assumption.

Not only me but lots of folks are not happy with duality. With that said I am trying to decide for myself what quanta of energy is in terms whether it is a wave or a particle. It cannot be both at the same time.

Unfortunately, you, or I, don't get to decide how Nature is, and She doesn't care about our cognitive or emotional burden in understanding Her.

In practice it's more complicated than that----it's a wavefunction of an electromagnetic field, whose base 'expansions' is in units of discrete energy states in some ways, and not a continuum thereof, that there is a 'constraint' linking frequency and intensity. For a given frequency, the allowable values of intensity (on certain observations) are not a continuum like Maxwellian electrodynamics, but a discrete comb. Now it's more complicated still, because you have a wavefunction which gives a probability distribution over these, so if your base photons have allowable energies 1hf, 2hf, 3hf, 4hf, etc...., the "state of the world" in a mixed state could still have energy 2.5 if you had a prob 1/2 of being in either the 2hf or 3hf state, and that wavefunction is apparently parameterizable by continuous numbers. But in certain kinds of observations you will get only the 2hf or 3hf with some probability.

So, yes, the physics of photons is sort of about being both wave and particle at the same time.

I look at photon as an event, instance of releasing or absorbing quanta of energy.

That's not a photon, that's an interaction with a photon.

If one were to change the permittivity of the vacuum for the EM how would that effect the other forces? Weak, Strong, Gravity etc...?

What is the opposite of time?

Can anyone please explain what the weak nuclear force is and what it's responsible for? Mostly interested in the Z Boson. What would happen if you had weaker Z Bosons, or if such a thing were to exist or be possible a Z Boson interacting with a more permeable Vacuum? Would that reduce your energy requirements to increase momentum or decrease it?

a reply to: mbkennel

In practice it's more complicated than that----it's a wavefunction of an electromagnetic field, whose base 'expansions' is in units of discrete energy states in some ways, and not a continuum thereof, that there is a 'constraint' linking frequency and intensity.

I understand what quanta of energy means more or less.

I think quanta travels in space like a wave. Meaning it is same amount of energy that was emitted from the source and received on the 'other end' (absorbed or measured) regardless how stretched it becomes while en route in space. And it comes in different 'sizes', not many.
By 'stretched' I tend to picture photon pulse leaving electron shell as a layer of the shell with shell shape wave resembling a donut only in 3d, growing outward)))). It has beginning and the end (boarders). As that ripple grows, donut 'walls' become thinner as length of the pulse front becomes wider. It is same amount of quanta only stretched as it grows as a ripple. When collapsed it assumes same shape as it left the source. I mean it should now read same wave length as it was in the moment of release. That's what I meant by photon being an instance (an event), because these two points can be measured and verified by measuring apparatus (wave length, amount of energy transferred, polarization and what not) but it will absolutely not mean that quanta was like that while en route through space. That's meaning of wave function collapse how I see it.

My bottom line is that logically collapsing the wave would involve the process of 'uncollapsing' the wave). Only these two instances will give proper wave length, for example.


Am I completely delusional? Is there some rational in my thinking?


cheers)

originally posted by: Signals
What is the opposite of time?

Emit.

a reply to: Bedlam

Ha, that's ynnuf.

What is charge? Is William Beatty's info sound? amasci.com...

originally posted by: DenyObfuscation
a reply to: Bedlam

Ha, that's ynnuf.

What is charge? Is William Beatty's info sound? amasci.com...

I'd tentatively agree. But I don't think of it in the terms he uses, generally.

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originally posted by: ErosA433
a reply to: MasterAtArms

Depends upon many factors such as mass and proximity,

The first thing that would happen is that they would get a huge burst of neutrinos. About 99% of the energy of a Supernovae is in neutrinos. Without looking at reaction types here, that could have some detrimental effect on the stars nearby, in terms of fusion at the core, but not enough to really cause say a failure of fusion. Next would come the photon and material energy as material is pushed away.

The photons would cause rapid heating of the outer envelope of the stars, this would cause them to puff out i think, so you would expect the star to become eggshaped or puffy facing the nova... all this wont matter too much (since most material wont have time to puff out anywhere) as the ejecta would smash into it.

Now, this is where size matters.

A large star might have its outer regions ripped off from the shockwave, but otherwise be unchanged, it might loose many solar masses if its a large star, possibly even change spectral type.

A smaller star however might have enough material removed that it simply dies itself... might be left with a puffy cloud that cools into a dwarf star.

Interesting question, and I hope some others weigh in too, these are my own ideas based just upon my old Astronomy notes

Great reply, thankyou! I wonder if there is any evidence of this in our own galaxy, given the enormity of the universe it must be happening somewhere once-in-a-while. If anyone else has any thoughts would be great

originally posted by: greenreflections
I mean it should now read same wave length as it was in the moment of release.

Most of the time in the lab that's more or less true, but there are exceptions. In one experiment about one in a million UV photons aimed into a crystal (I think) split and when you measured that millionth photon and its partner they were exactly half the energy of the original, so you got two quanta for the price of one quantum though at half the frequency.

However I suspect it's probably false for the vast majority of all photons in the universe where the final wavelength is always lower than the initial wavelength which happens without any of the aforementioned splitting. If we observe photons coming from outside our tiny corner of the universe in the "local group", they all have longer wavelengths than when they were emitted.

That's what I meant by photon being an instance (an event), because these two points can be measured and verified by measuring apparatus (wave length, amount of energy transferred, polarization and what not) but it will absolutely not mean that quanta was like that while en route through space. That's meaning of wave function collapse how I see it.

It's still the interaction that's the event, not the photon. Words have meanings.

Am I completely delusional? Is there some rational in my thinking?

I think you have some lack of familiarity with terminology and lack of familiarity with experimental results, but aside from those gaps it seems to me like you're trying to use sound reasoning and as I said your photon description didn't sound much different to me than the physicist's description once those issues were set aside. The ultimate arbiter is how well what we say matches up with experiment. You never answered my question about whether you had experimental evidence to support your claim that a single photon could be detected by more than one detector in a detection array.

If we have different ideas about what happens beyond the experiments then it's hard to say who is right and who is wrong, which was the whole point of the video by Sean Carroll in the opening post. He's got one idea, other scientists have other ideas, and he admits he could be wrong and they could be right since there are no experiments to confirm any of the interpretations. As long as he can admit the possibility his speculations might be proven wrong by experiment, there's nothing delusional about his speculative views even though they sound somewhat crazy to some people. So if you follow his lead in areas where you're speculating and admit you might be wrong, I don't see a problem with that, but I'm pretty sure you were wrong about a single photon being detected by more than one detector.

a reply to: greenreflections

I think that's how most people visualize it with a classical physics intuition, but I'm not sure it's right, or can even be visualized intuitively in any way.

You're thinking about probability density radiating like energy density. Maybe?

I wouldn't call the photon to be the same thing as an event, but it is true that they are measured in physical events.

a reply to: KrzYma

I really enjoyed the video. Tyvm for that.