What I understand about photons (and some that I may misunderstand) is that it is the particle that carries electromagnetic radiation but has no weight. However, it is a real particle and can travel through a vacuum. Because it is a particle, it has mass (I presume.) In its most energetic form it causes gamma radiation, and in its least energetic form it’s microwave. Is that the lowest energy form or are there lower ones? If it has mass, why doesn’t it have weight?
It is my understanding that a photon is a quantum particle that has no mass. So I believe you’re starting with an incorrect presumption.
It has no mass, and can therefore have an arbitrarily low energy. Microwaves aren’t even a practical lower bound: Radio waves are much lower energy.
as Quicksilver said, photons have zero rest mas. They can, however, carry momentum. That might seem like a contradiction, but if photons had any mass at all they would have infinite momentum when travelling at the speed of light, which is how fast photons travel.
Microwaves, which span about from about 300 kHz to 300 MHz, aren’t by any means the photons with the lowest energy. Radio waves are lower, then there are a succession of ever more depressingly-named strata until you get to Extremely Low Frequency (ELF) waves, going down to about a Hertz. There’s no reason you couldn’t go lower, but this is bout as far as meaningful discussion goes.
Photons are extremely weird and interesting things. I notice that when people try to draw them they invariably depict them as hard spheres with a well-defined radius, but that’s absurd for all sorts of reasons. In the first place, you see by receiving photons, so what would you see such a photon with? In most cases you see an object because light bounces off it, but scattering of a photon by a photon has an extremely low probability (but not zero). The biggest problem, though, is that a photon almost certainly doesn’t have a hard, strictly limited range of action. I mentally picture a photon as a sort of dust ball which thins out the farther you get from the center, but which never really drops to zero, kind of like the quantum mechanical image of a hydrogen atom. A single photon will pass through a very narrow opening, but will interfere with itself, producing a contribution to the interference fringes you see. But a photon passing through a large opening, a few millimeters across, will still interfere with itself, meaning that it “senses” both edges of the slit.
Incidentally, while nobody much cares about photons with a frequency less than 1 Hz or so (corresponding to a period of 1 s), there is actual research done on the topic of gravitational waves (which are qualitatively very similar to light) with periods as long as years, and correspondingly low energies. In fact, the highest frequencies of gravitational waves that anyone expects to ever actually encounter are only in the few kHz range.
Scientists have claimed they have “heard” a black hole"
I can name that tune in 30 million years!
Nitpick: They’re not hearing the sound there; they’re seeing it. The sound from the black hole is causing subtle changes (density fluctuations, I think) in the not-quite-a-vacuum surrounding it, and we’re able to see those changes. The sound isn’t actually reaching us.
A photon has no mass in the same way as an ocean wave has no mass. A tsunami is a massless entity that is created by an energetic event and can wreak a lot of damage but has no actual mass in and of itself. This is fundamentally analogous to a photon, which is at the heart of the particle/wave duality issue.
They also, AAUI, have no actual reference frame. Relative to us, they travel at the, uh, speed of light, so time stands still for them, at least relative to us. To a photon, the moment it is created and the moment it is reabsorbed is the same event. What I am not entirely clear on is refraction, which causes photons to travel at a reduced speed through a transparent medium. I think that this has to do with the medium capturing photons and re-emitting them, but given that any thing is composed of mostly empty space, there must be some kind of EM attraction that draws photons toward atoms/electrons to stop them from just passing right through (because, well, they tend to be kind of small).
Things are not composed of mostly empty space. They’re chock full of fields. The photon and electron fields that fill solid objects might not be as dense as the nuclei, but they’re most emphatically there.
Well, empty space itself is not very empty. I doubt there is a true vacuum anywhere in the observable universe.
It isn’t just that there might be the odd real particle or two in the bit of “empty” space, but intrinsically, nowhere in our known universe (observable or not) does the core nature of space itself allow it to be truly empty.
Even if you shield out the CMBR, cool everything to as near as absolute zero as engineering limits allow, and so on, there is still an intrinsic filling of all the fields and their quantum fluctuations. No matter what, your lonely photon crossing this space has stuff to interact with, and the rules of QED will tell you how it behaves.
Nitpick: While different definitions exist for Microwaves, none of them are at such low frequencies. A common definition is from 1 GHz to 100 GHz (30 cm to 3 mm wavelength), though often the term millimeter waves is used above 30 GHz, where the wavelength is shorter than a cm and conveniently measured in millimeters. Microwave ovens typically work at about 2.5 GHz.
That seems like a distinction without a difference. An ordinary microphone also doesn’t “hear” anything; it senses a difference in capacitance, or resistance, or magnetism, or even uses optics to sense movement. Human hair cells in the ear use pressure to mechanically open an ion channel, creating an electrical potential than can be measured.
Of course, the difference here is that the sensing medium is very far away, but that’s commensurate with the general massive scale of things. But the fact that they use optics to sense the movement (I presume using Doppler shifts) isn’t fundamentally different from any other sound sensing device.
Well, if you’re calling the interstellar medium in that galaxy part of the microphone, then I guess you could say they’re hearing it. But I don’t think it’s a distinction without a difference to say that no sound is reaching any instrument built by man.