Free-space electromagnetics is essentially perfectly linear at technologically-accessible energy densities. A heavy ion has very large local EM fields. If observed from another ion coming in with high energy, that field appears to turn on and off very rapidly. Even considered classically, that has a fast AC component.
So it's quite an extreme environment.
Cheers
Phil Hobbs
Since we can image basically point sources and fast events from billions of light-years away, I guess photons don't interact much.
Gravity does bend light, so gravity waves must scramble it a bit.
It's impressive, and nice, that we can see stuff from light-years away. It's impressive that we can even see the sun and moon and stars. Imagine how physics would have developed on a cloudy planet.
Could be even worse than that, some may remember that:
See "Life, The Universe, and Everything" by Douglas Adams. ;)
Cheers
Phil Hobbs
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Joe Gwinn
Oh, a pair-production event could happen in a vacuum, BUT the flux of photons at 511 keV would have to allow for two to collide, AND the cross section for that event is so small, that our universe just isn't big enough, or old enough, to expect to see it happen.
Once the photons generate the electron/positron pair, it's not 'in a vacuum' anymore.
Do you know of a device that emits single photons on command? Detecting light is very much a crapshoot. With very weak light in short pulses, you get mostly nothing, sometimes one, and very rarely two events, in addition to events when there is in fact no light at all.
Why do you suggest communication is necessary between points on the detector?
Jeroen Belleman
It's possible. There are traps where one can park an ion, and only ONE single ion, and which will fluoresce when given the right illumination. So, shine the illuminator for a time short compared to the fluorescence lifetime, and you can expect one photon emitted thereafter.
Dimiter_Popoff snipped-for-privacy@tgi-sci.com wrote in news:sf963d$h89$ snipped-for-privacy@dont-email.me:
Now that is a weird reference.
Jeroen Belleman snipped-for-privacy@nospam.please wrote in news:sf9c86$1o4u$ snipped-for-privacy@gioia.aioe.org:
Solid State, single photon emitter.
F4 Phantoms had a rearward facing PMT that was said to be able to detect single photon events, such as a ground based missle launch, etc.
You should check out what they are doing way down in a hole in the ice in Antarctica.
whit3rd snipped-for-privacy@gmail.com wrote in news: snipped-for-privacy@googlegroups.com:
Reference?
Jeroen Belleman
Try
Warren Nagourney buttonholed me in the hall, and I actually saw a single atom (trapped, and fluoresceing) some decades ago. Smallest thing one can see with the naked eye, but if it had been TWO atoms... I wouldn't have been able to tell.
Statistically, yes. There's been a lot, a lot of work on single-photon sources in the last 20 years or so.
Because you never get more detection events than permitted by the pulse energy, even though one area of the detector (even in principle) can have no information about whether they've already been detected elsewhere.
Cheers
Phil Hobbs
This view is the Copenhagen-style collapse of the wave function, which I am convinced is wrong. There's no such thing as 'never' in these matters. It's just very unlikely.
Light detectors are noisy. You *do* get events even when there shouldn't be any.
Jeroen Belleman
I'm not talking about any interpretation, I'm talking about experiment.
Cheers
Phil Hobbs
As ironically stated by the John Doe snipped-for-privacy@message.header troll in message-id <sdhn7c$pkp$ snipped-for-privacy@dont-email.me who has posted yet another incorectly formatted USENET posting on Mon, 16 Aug 2021 23:10:21 -0000 (UTC) in message-id <sfer8t$5df$ snipped-for-privacy@dont-email.me.
But the simplest system it is a property of is an ideal vacuum.
I have often wondered what the wavefunction of a nominally monochromatic laser source photon looks like when you Q gate those you let out it to the point where df/f is quite large. The photons (wavefunction) clearly had a well defined frequency before they were allowed out of the cavity.
But afterwards to match the boundary conditions they have a much wider spread of possible frequencies.
The intensity optical interferometer is particularly challenging to explain without some way of having photons correlated. Before it was built several eminent scientists insisted it would never work.
+1I'm with you on a perfect vacuum being the original ideal medium for EM waves. Although a real vacuum also has virtual particles flickering in and out of existence (and also a trace of neutral hydrogen or plasma). The main difference is you get a slight rotation of polarisation and frequency dependent propagation speed in an imperfect vacuum.
Corrections for these experimental quirks have caused the official speed of light to vary quite markedly over the years with tight formal error bounds but significant systematic error in one of the techniques. ISTR it was only discovered when a new microwave method disagreed.
There is a textbook around in the 1970's that had this graph in from Romer onwards with error bars and a discussion. I cannot recall the title. Does anyone recognise it from this description?
I'm sure you know the speed of light is now defined exactly:
Speed of light
The speed of light in vacuum, commonly denoted c, is a universal physical constant important in many areas of physics. Its exact value is defined as
299792458 metres per second (approximately 300000 km/s, or 186000 mi/s). [Note 3] It is exact because, by international agreement, a metre is defined as the length of the path travelled by light in vacuum during a time interval of 1?299792458 second.[Note 4][3] According to special relativity, c is the upper limit for the speed at which conventional matter, energy or any signal carrying information can travel through space.
I don't really see a problem. When you gate an EM wave, either spatially or in time, you get sidebands. It's when you try to reason in terms of photons that you get into trouble. Anyway, even the QM maths to model these effects are really wave maths.
A remote star, for any practical purpose, is a point source. How could it be anything but coherent? Yes, the spectrum is still basically thermal, so the coherence length is minuscule.
Only where interactions occur. No matter is needed to just propagate EM waves, even though I find that hard to accept too.
Virtual particles arise from the same reasoning that grants a physical existence to photons, so ...
Jeroen Belleman
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