Im a blue collar worker, just had a thought. What would happen to photons that never hit anything. It must be possible that at least one photon out there somewhere just happened to not ever hit anything. Would it ever change states? Does it become dark matter? I googled a bunch and checked on here i couldnt find a similar question.
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3$\begingroup$ If it does not interact with anything, then it will stay itself and keep moving forward. It is, however, possible to bend a ray of light. $\endgroup$– naturallyInconsistentCommented Jul 22 at 2:04
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3$\begingroup$ The main problem with the question is that "photons" are not atomistic constituents of light. They are the amounts of energy that the electromagnetic field exchanges with systems that emit and absorb radiation. In essence there are no photons unless light is being emitted or absorbed somewhere. $\endgroup$– FlatterMannCommented Jul 22 at 2:15
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1$\begingroup$ @FlatterMan photon exist as they propagate, even before they are detected. How do you think they got there. I understand that they are not perceived as light until something can detect them but that doesn't mean they're not there. Many things fall into that type of situation. If someone throws a rock at you and you don't see or know its coming until it hits your head, you can't say it didn't exist until you absorbed it, I mean felt it. $\endgroup$– Bill AlseptCommented Jul 22 at 4:20
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$\begingroup$ Since the universe is expanding everywhere, you don't have to worry about the photon hitting the "Edge" , as evidenced by galaxies that are moving [expanding] away from Earth so fast that their light will never reach us. $\endgroup$– Carl WitthoftCommented Jul 22 at 11:56
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$\begingroup$ @BillAlsept You are welcome to tell us which experiment demonstrates propagating photons. I have never seen one. I do, of course, understand that the classically trained human mind wants to interpolate things at all cost. In quantum mechanics the cost of that interpolation is a logical error. $\endgroup$– FlatterMannCommented Jul 22 at 22:33
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1 Answer
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The Cosmic Microwave Background is light that was emitted at the beginning of the universe, shortly after the Big Bang.
It has been traveling ever since. That was 13.7 billion years ago. The light is now far older than the earth, which is about 4.5 billion years old.
As it traveled, the universe expanded. This slowly stretched the wavelength of this light. Visible light became redder, then infrared, and eventually microwaves.
Today, those waves can be detected as some of them hit the Earth. We have learned a lot about the early universe from them.
Light usually travels in a straight line. However, gravity can bend light. This was one of the first things Einstein discovered when he thought about the implications of General Relativity. He predicted that if light from a distant star happened to pass very close to the Sun, it would be deflected about $1/1000^{th}$ of a degree. This turned out to be right.
Sometimes light from a really distant galaxy passes by another galaxy or a group of galaxies on its way to Earth. These are large enough to bend light significantly. Their gravity can focus light, like a giant lens. This is called Gravitational Lensing. Sometimes it magnifies the distant galaxy. Sometimes it distorts the image of the distant galaxy. It allows us to see a few galaxies that would otherwise be too faint for even the largest telescopes.
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$\begingroup$ So as it moves (exists) its wavelengths change, so if it became as you said microwaves. Then what happens after that. It would only makes sense that it would continue to change or else reach a point where it starts to go into a different (possibly negative) state. $\endgroup$ Commented Jul 23 at 0:17
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$\begingroup$ The wavelength is continuing to grow. $\endgroup$ Commented Jul 23 at 1:29
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$\begingroup$ It cant grow infinitely. Nothing does $\endgroup$ Commented Jul 23 at 5:18
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$\begingroup$ Other wise my gf would be satisfied $\endgroup$ Commented Jul 23 at 5:18
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$\begingroup$ @SeanBrittain Wavelength is proportional to one over energy and energy can go to zero, hence wavelength can actually go to infinity. $\endgroup$ Commented Jul 23 at 8:22