Ask any question you want about Physics

a reply to: darkorange

Not to attempt to answer for ErosA433 here, but doesn't that lie in the wave-particle duality? It can be categorized as a wave until interacting with something else, at which point the wave function collapses into a particle with specific location.
At least, that's what I gathered from the Reading Rainbow episode where they covered quantum theory.

originally posted by: pfishy
a reply to: darkorange

Not to attempt to answer for ErosA433 here, but doesn't that lie in the wave-particle duality? It can be categorized as a wave until interacting with something else, at which point the wave function collapses into a particle with specific location.
At least, that's what I gathered from the Reading Rainbow episode where they covered quantum theory.

IMO, you are absolutely right. If I read you correctly. Wave leaves a flash on detector surface when it encounters energy pulse. That is photon, bit of energy wave. I just don't like wave-particle duality definition. It makes one believe there is a mystery of what elementary particles are. Something like photon.

Photon is statistical unit. A bit.


cheers))

..and I find confusing the term 'wave function collapse'. No wave is collapsing. It just has its energy sum diminished by the bit that contributed to the detector surface. ) Wave continues to expand. No 'collapse'.
Nothing like soap bubble YT wants you to believe.

cherrs)

a reply to: Arbitrageur

Does time really exist? Or is it just gravity, and we invented time?

If I shoot highly concentrate pulse with water gun under the water? The pulse would live as defined 'bullet' for a time being. Eventually it would dissipate into surrounding water body.

That's what photon does on emission.


No?

originally posted by: yulka
a reply to: Arbitrageur

Does time really exist? Or is it just gravity, and we invented time?

the flow of time imo is direct evidence that space is expanding.


cheers)

originally posted by: yulka
a reply to: Arbitrageur

Does time really exist? Or is it just gravity, and we invented time?

It's not just gravity because you get the same type of time dilation whether your acceleration is from a gravitational field or from a rocket which is accelerating you in the absence of any significant gravity.

It was a major paradigm shift to accept that time is not absolute like many people accepted without question before Einstein's relativity. But just because it's relative doesn't mean it doesn't exist.

originally posted by: darkorange

originally posted by: yulka
a reply to: Arbitrageur

Does time really exist? Or is it just gravity, and we invented time?

the flow of time imo is direct evidence that space is expanding.

I'm trying to keep this thread somewhat within the realm of real science. Fringe topics can be discussed if there are perhaps controversial papers published. However that's not a question, and the topic of the thread is "Ask any question you want about Physics".

If you want to make something like that on topic, phrase it as a question, like "is the flow of time direct evidence that space is expanding". What evidence leads you to that idea? If the universe was contracting, time would still be flowing, wouldn't it? If that's true then it proves your statement false. If you think it's not true maybe you can explain why.

a reply to: Arbitrageur

It was a major paradigm shift to accept that time is not absolute like many people accepted without question before Einstein's relativity

Is it the 1905 paper?

this way there will be one hundred topics per day if we ask own questions about physics. Just let people talk. It was a good idea to start general topic like that. and thank you for doing that.

originally posted by: darkorange
this way there will be one hundred topics per day if we ask own questions about physics. Just let people talk. It was a good idea to start general topic like that. and thank you for doing that.

Feel free to start your own thread called "Just let people talk" if the mods will allow it.

The topic of this thread is "Ask any question you want about Physics". I'm not very strict about the topic, but "Just let people talk" is going too far.

I haven't had much problem with off-topic since the 911 folks left and since the guy who claimed to prove time travel with the brightness of two candles left and I'd like to keep it that way. I wasn't going to let him talk because what he said had little relevance to physics, but he was welcome to ask questions and so are you.

On photons its always about how we understand wave-particle duality

There are a few different experiments that we can perform using the setup i had and the devices i had available.

Firstly my photon source was an LED pulser, it would give me a sharp picosecond rise time flash of light, with a width of about 2.5ns, each flash, when the LED is operated at full intensity was giving around 10^9 photons with about 5% pulse to pulse variation.

So what does this look like in a detector?

Well at full intensity you get a rediculously large pulse, for us I was using a high bandwidth current to voltage pre-amplifier and when we saturate it, we basically get a huge 5 volt spike, and then a decay time related to the discharge of the photo-diode capacitance. So for photon counting, thats not so useful.

Interesting question is this... can you see it with the naked eye? A single shot, no you cant. Iv tried... and iv never been able to see it over ambient. Dark adapted, you can just about see it... the reason is that the pulse is very fast, and it doesnt activate the retina for long enough for your brain to register it.

OK so what do we do? We have two options, you run the LED at its threshold voltage (this is when the voltage is just enough to make it shine) OR you use neutral density filters.

I used calibrated filters to give me a 10^9 reduction in light, to the eye, there is no light coming from the filter. To the Avalanche Photodiode (In my case a multi-pixel one) with each flash of the LED it will see occasionally a single photon, sometimes two, sometimes three.

This is significant because the MPPC operates in Geiger mode, which means once a pixel activates it discharges and gives you a fixed charge output... doesn't matter if you hit the pixel with 1 or 50 photons, you see a binary 1.

So for a filtered LED flasher with a mean number of expected photons of 1, seeing 3 pixels fire, does mean that the device was activated by 3 separate photons.

The energy of the photon is used to create an electron-hole pair in the semi-conductor, the energy required to do this depends upon the p-n junction, doping materials and if it is standard or reverse structured. Basically the minimal energy required for this device is a few electron-volts, which means infra red wavelength light. So the device is sensitive to I-R, and in the blue it is limited by the absorption of blue and UV light by the silicon (basically blue light gets absorbed by the surface layers and doesnt reach the p-n junction)

So the activation of 3 random pixels on the device, means that 3 'things' separated in physical space, imparted energy in the device. these 3 'things' where all of roughly the same energy (and thus wavelength), they also arrived within a few picoseconds of each other.

So that doesn't really separate things right? is it a wave or is it a particle. you might say 3 different waves came out of the LED and struck the sensor in 3 different locations.

My point is that 1) im not making this stuff up, i know quite a lot about photon counting and characterizing sensors and 2) if the photon was a long wave that stretched out until it his something, you would not expect quantized observations like this. the sensor would activate fully as a wavefront hit it, the wavefront here being when the flash starts. The device behaves exactly like a low numbers counting system, it is Poisson distribution.

Wave particle duality does also require that photons can be split into distinct energies or wavelengths, we can observe how the device behaves differently when different wavelenghts activate it.

in the case on an MPPC, the avalanche can produce Infra red radiation due to electron-hole re-combination, why does it matter you ask? Well because with an IR camera it is possible to see which pixels activate. You can also do something cleaver which is to use two LEDs to give you two different wavelengths, and observe how the pixels activate differently, and yet still maintain a binary like activation.



Now thats a long of text, but the point here really is, that the image of light emanating from a source as some nice ripple wave out like waves on a lake, just isn;t how light is. If it was that way, we would NOT observe what we do in the above experiment. if you filtered the light down, you would expect to see the whole detector activate, or nothing, your wave will pass through the filter, or it wont. If photons however are quantized... the filter may let single ones through. The intensity being set by the number of single photons... and not the imaginary 'height' of the wave front, which is how some people want to see it or propose it is

Here is a lecture I found on tachyons to clarify. Her explains why they don't move faster than light as well as why you can't plug it in to Einsteins equations to get an answer. He will discuss tachyons at about the 58 min mark. But to understand why I suggest watching earlier on ground states.

originally posted by: yulka
Is it the 1905 paper?

Yes but Einstein's 1905 special relativity paper said nothing about gravity. Since your initial question was about gravity you have to refer to the later paper on general relativity for that.

a reply to: dragonridr
One topic that interests me is misnomers in science.
That's why I made a thread about the Earth's north magnetic pole actually being a south magnetic pole, but that at least was an accident.

This tachyon confusion is worse because it was apparently intentional to add a subluminal use of the word which originally meant superluminal, which I think creates confusion about what Tachyon really means. Even the guy in the video you posted admits it originally meant a faster than light particle, and now some string theorists decided to try to confuse people by saying it means something else. They should have picked another word for the subluminal concept besides "tachyon", but yeah he's right there are string theorists who have usurped the term and distorted its original meaning, and Susskind is aware this is what happened though he doesn't recall which string theorist to blame. Physicists are usually somewhat particular about their use of terminology, but on occasion they get a little sloppy and this "tachyon" seems to be to be an example of the latter. At least it's not a serious issue since superluminal tachyons probably don't exist.

This reminds me of the example of "aether". Without any qualifiers we generally presume the term today refers to luminiferous aether which like the tachyon, we believe to not exist.

Then Einstein came along and said you can think of his "space-time" in GR as a "New aether" with different properties from luminiferous aether. There were already at least 4 other kinds of aether besides "space-time" so it's a good thing that Einstein's proposal to use the same word "aether" for yet a 5th thing never caught on, so now we call it "space-time" instead of aether.

If it's something else, we should call it something else. We did with space time but not with "subluminal tachyons" or "tachyon fields". If we're talking about negative mass why not call it "negative mass", which would be descriptive, or coin a new term that doesn't imply superluminal. Apparently in general use the tachyon particle thought not to exist would travel faster than light but the tachyon field from string theory is not faster than light. Here is a good FAQ on the former:

Do tachyons exist?

Now the fundamental fact of relativity is that
E² − p² = m²

where E is an object's energy, p is its momentum, and m is its rest mass, which we'll just call 'mass'. In case you're wondering, we are working in units where c=1. For any non-zero value of m, this is a hyperbola with branches in the timelike regions. It passes through the point (p,E) = (0,m), where the particle is at rest. Any particle with mass m is constrained to move on the upper branch of this hyperbola. (Otherwise, it is "off shell", a term you hear in association with virtual particles — but that's another topic.) For massless particles, E² = p², and the particle moves on the light-cone.

These two cases are given the names tardyon (or bradyon in more modern usage) and luxon, for "slow particle" and "light particle". Tachyon is the name given to the supposed "fast particle" which would move with v > c. Tachyons were first introduced into physics by Gerald Feinberg, in his seminal paper "On the possibility of faster-than-light particles" [Phys. Rev. 159, 1089—1105 (1967)].

Now another familiar relativistic equation is
E = m[1−(v/c)²]−½.

Tachyons (if they exist) have v > c. This means that E is imaginary! Well, what if we take the rest mass m, and take it to be imaginary? Then E is negative real, and E² − p² = m² < 0. Or, p² − E² = M², where M is real. This is a hyperbola with branches in the spacelike region of spacetime. The energy and momentum of a tachyon must satisfy this relation.

The guy who wrote that FAQ is not a crackpot and Susskind was out of line to call people that talk about faster than light Tachyons "crackpots". We can talk about that idea but I guess if someone believes they exist when evidence shows they don't that might make make someone a crackpot.

How would Susskind like it if people called string theorists crackpots? There may be no evidence for superluminal tachyons and they probably don't exist but I don't see evidence for string "theory", I mean hypothesis, either.

a reply to: ErosA433
You know a lot more about photon detectors than I do. I noticed those photon detectors you linked to had detection efficiencies from 25% to 40% which is not bad considering how small they are. I didn't see any cryogenics shown in the photos. I saw someone from NIST saying they had single photon detectors with much higher detection efficiency but it was a huge apparatus which had cryogenics, I suppose to cool things down and lower the background? I didn't really look into the details of how it worked but that was my guess.

originally posted by: darkorange
If I shoot highly concentrate pulse with water gun under the water? The pulse would live as defined 'bullet' for a time being. Eventually it would dissipate into surrounding water body.

That's what photon does on emission.


No?

No. UNDER the water, you'd have to have a longitudinal wave. No soliton for YOU.

This, by the way, is a reason you can't have aether. If "luminiferous aether" were everywhere all the time, any EM wave that depended on "aether" in which to propagate would HAVE to be longitudinal also, like a Bearden scalar wave.

However, we know it's not, because the LCD screen in front of you works. Therefore, light is transverse, and there is no aether. Sim, salabim!

a reply to: Bedlam

I have a question instead of a luminiferous aether could there be something more like a quantum potential aether. Everything being a ghost particle or virtual in some sort if pseudo wave like state until there is enough potential for said particle to manifest or percolate out of that aether by whatever mechanism?

Please put on the soft toes boots before you give me swift one up the you know what for asking more stupid questions this time. My butts a little sore from the last time. I think one of you was wearing doc martins.

a reply to: Arbitrageur

And some people are so fond of saying that Einstein killed the aether. But he used the term himself, to some extent.
Also, my idiotic little wad of gray matter kept insisting that you were typing 'subliminal' tachyons. Which, if I recall correctly, are indeed subluminal, but they keep trying to quietly trick you into smoking and buying snacks at the theater.

a reply to: Bedlam

I get almost everything you said there, except your insistence that I'm viewing this site using an LCD display. I'm still rocking an old school CRT smartphone...
But to get to the actual point and save you from any more of my ridiculous attempts at humor, would you mind explaining scalar waves in a bit more depth. I understand the basic difference between longitudinal and scalar waves from a geometric perspective, but what supposed ability do they have that makes them such a staple of conspiracy theories?

a reply to: BASSPLYR

Wouldn't that be something along the lines of the "quantum foam", which is theoretically all-pervasive. If the theory is viable of course.

a reply to: BASSPLYR
If you replace the word "aether" with "fields", that description somewhat resembles field theory where we say a particle is an "excitation" of a field.

profmattstrassler.com...

A virtual particle is not a particle at all. It refers precisely to a disturbance in a field that is not a particle. A particle is a nice, regular ripple in a field, one that can travel smoothly and effortlessly through space, like a clear tone of a bell moving through the air. A “virtual particle”, generally, is a disturbance in a field that will never be found on its own, but instead is something that is caused by the presence of other particles, often of other fields.

a reply to: Arbitrageur

Could you possibly explain the concept of quantum foam, if you don't find it too ridiculous?