That was the point though. Some are close enough for the difference to be detectable. They are resolved on suitably long baseline.
Michelson & Pease first did it two slits style on the Mount Wilson 100" scope with an iron beam across the front. It took two great experimentalists to make it work back then!
The intensity interferometer is quite amazing. It was used to measure stellar diameters back in the 1960's using 931 PMTs and searchlight reflectors as photon catchers. The second generation instrument at Narrabi was very impressive - and explanation of exactly how it works at a quantum had to wait for the 2005 Nobel Physics prize.
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I can't find the article not behind a paywall celebrating its 50th anniversary. ISTR Phil has the (rare) book online somewhere.
And you can detect their existence as the Casimir effect.
A very good read. RHB started out in radio and infrared. Classically it's not too hard to take the angular spectrum of a thermal source, compute the expected (classical) fluctuations, and use diffraction theory to show how the cross-correlations change with receiver position.
The quantum folks of the day thought that that didn't apply to light from different sources. It was held that light from independent sources could never interfere, whereas they (paradoxically) had no problems tuning in the BBC on their table radio, whose superheterodyne design used the exact same principle.
Yup.
I'm very sympathetic to Jeroen's position--it really is unsatisfying that we don't have intuition of how quantum mechanics works. The ancient Greek philosophers spent centuries sorting out issues of being, essence, identity, and so on, based on sharp reasoning from common notions and observation.
The truncated version of their work that's our common coin ignores spiritual realities, but apart from that rather recent mistake, their notions have held up pretty well for over 2000 years.
At macroscopic levels, they still do. One major problem with them is that they tend to lead to the error of philosophical determinism, with its well-known inhumane consequences and other absurdities such as the abolition of the possibility of logical thought.
Quantum folks like Sabine Hossenfelder (and many before her) try to preserve the determinist view by saying that the equations of quantum mechanics are linear, so that the wave function at any time t is completely determined by its form at earlier times.
That's true unless there are state transitions involved, but then state transitions are occurring randomly everywhere, so that new information is appearing in the universe on a massive scale at all times.
On a sunny day (Tue, 17 Aug 2021 21:39:47 -0400) it happened Phil Hobbs snipped-for-privacy@electrooptical.net wrote in snipped-for-privacy@electrooptical.net:
The physics peers make it so. Take the example of 'virtual particles popping in and out of existence in a vacuum." To me, when somebody refers to 'virtual' that suggest something not real. Mathemamaticians are good in that: (singularities as example divide by zero, re-normalization etc ?' Anyways, IF (Hello Jeroen) we look at a Le Sage theory of gravity, and just say for a moment these particles actually move at light speed, and EM waves are just the same particle in a different state, we united everything. We see then, from reasoning, that in free space (vacuum as physics thinks) there must also be collisions between these Le Sage particles, are those collisions fully elastic? what happens when more collide together? What happens when EM type and non EM type collide? There are your virtual particles, everywhere. Without a _mechanism_ any theory immediately becomes philosophy and mathematical divide by zero crap.
The papers Jeroen mentioned actually relate to the same model / issue I am referring too, no empty space!
Not saying my way is right, but it does well explain and predict. Ad the variable light speedS (capital S because of multiple big bangs) and let's look a bit better at all the measurements and not ignore the outlayers because 'obviously it must fit Neinstein and C). Else we will be here in circles doing the divide by zero virtual reality illusion till we go dinos way.
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