Sound can be described in terms of particles (or more accurately quasiparticles), so-called phonons, all right—they’re the excitations of the field of vibrations of the underlying material, which can (and has to be) described in quantum mechanical terms. As such, there is no limit to their propagation (other than, of course, the limits of the material).
And it is possible for some individual photons to have less energy than other individual photons. But that doesn’t mean that the light is dimmer; it means that it’s a different color. Red photons have less energy than blue photons, infrared photons have less energy yet, and microwave and radio wave photons have even less energy (though it’s very rarely useful to talk about individual photons of radio waves). On the other end of the scale, ultraviolet, x-ray, and gamma ray photons, in that order, have more energy than blue photons.
And in an arena - QED - where pretty much all accepted theory is non-intuitive (IOW, silly).
As Riemann said, sound pressure waves are absorbed by matter and converted to a tiny amount of heat. Afterward there is no information content left of the original sound wave. It is not still faintly bouncing around the room.
Here is an analogy to help understand it: microwave beams are often used to transmit data. If sufficiently powerful they can heat water-containing objects, as in a microwave oven. However if you heated a potato with a powerful data-carrying microwave beam, that information content is lost. You cannot analyze the resulting thermal vibrations (ie heat) in the potato and recover the information content from the beam. It’s similar with sound. After it is absorbed by matter and converted to heat, even if the heat itself was detectable there would be no correlatable information content related to the sound. There are no faint acoustic echoes bouncing around of dinosaurs.
This is different from electromagnetic radiation. If you could travel faster than light then build a sufficiently large telescope pointed at earth you could theoretically take pictures of dinosaurs. Or an alien race millions of light years away could do that, given sufficient technology. However the same thing cannot be done with sound.
Re “few pixels around the universe”, sound cannot travel in the vacuum of space. Any acoustic sound that happens on earth will be restricted to earth’s vicinity.
Every atom on Earth is vibrating a bit. If a sound wave passes through it vibrates a little more and makes a nearby atom vibrate a little more which makes another nearby atom vibrate a little more.
But each time the chain of vibration passes, the next atom vibrates a little less and a little less. And when the amount of vibration passed to the next atom is a lot less than the average random vibration of an individual atom, you can’t detect the signal any more, it’s all been converted into heat. And heat just means random vibrations of atoms.
Apologies for the hijack, but…if the universe is 13.8 billion years old, how can there be an object 32 billion light years away?* And how could we see it? Wouldn’t the light take longer than the universe has been around to reach us?
*And Wikipedia says that’s “comoving distance,” meaning the expansion of space has been factored out.
When the light started moving, the Universe was smaller. So, for instance, it made the first half of the journey in less than half of the time.
Here’s a similar discussion about the number of photons emitted from a star, but with actual numbers.
https://www.reddit.com/r/askscience/comments/1hmiuc/how_many_photons_does_a_star_produce/
[QUOTE=Sailboat]
Apologies for the hijack, but…if the universe is 13.8 billion years old, how can there be an object 32 billion light years away?* And how could we see it? Wouldn’t the light take longer than the universe has been around to reach us?
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There’s some additional weirdness.
The most distant objects that we can now see from the early universe were receding at more than the speed of light when they emitted the photons that we see, and they have continued to do so ever since. Yet we still see them! Consider the photons that these objects emitted in our direction. In the local space of the objects, the photons were sent off towards us at the speed of light, and relative to their local region of space the photons have always moved in our direction at the speed of light. But initially, the superluminal recession of that region of space meant that the net movement of those photons was away from us. As the photons moved through space that was receding at progressively lower velocity, the net movement of the photons away from us gradually decreased until they were “stationary”; and then they found themselves in space that was receding at less than the speed of light, gained net movement towards us, and eventually reached us billions of years later.
Expanding Confusion: common misconceptions of cosmological horizons and the superluminal expansion of the Universe
[QUOTE=Davis & Lineweaver p9]
Our teardrop shaped past light cone… shows that any photons we now observe that were emitted in the first ~five billion years were emitted in regions that were receding superluminally. Thus their total velocity was [initially] away from us. Only when the Hubble sphere expands past these photons do they move into the region of subluminal recession and approach us. The most distant objects that we can see now were outside the Hubble sphere when their comoving coordinates intersected our past light cone. Thus, they were receding superluminally when they emitted the photons we see now. Since their worldlines have always been beyond the Hubble sphere these objects were, are, and always have been, receding from us faster than the speed of light.
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Even more weirdly the angular size of an object (i.e. how large it appears) starts getting larger for objects beyond about 20 billion light years. That is to say a galaxy 30 bn ly away takes up more of the sky than a galaxy the same dimensions, viewed from the same angle, that is 20 bn ly away. This assumes the standard cosmological model.
You seem to equate the photon’s energy with the [del]wavelength[/del] amplitude(?). I can accept that easily. But them I’m wondering: What causes brightness and dimness? It is simply high and low numbers of photons?
If this thread is going to distinguish between “mindbogglingly large” and “infinite”, then we must also distinguish between “mindbogglingly small” and “zero”, in which case…
But there is no total vacuum. Not between galaxies, and certainly not between planets. An acoustic sound that happens on earth will eventually reach the upper atmosphere - weak though it be - and from there it will travel onwards and outwards. The molecules in the upper atmosphere will occasionally and rarely - but more importantly eventually and definitely - bump into other molecules, which will carry the sound further. (Subject, of course, to the questions raised above as to whether the strength of that sound might go below some Planck limit.)
The energy of each photon corresponds to its wavelength. Specifically, a photon’s energy is inversely proportional to wavelength.
Yes, it’s the number of photons that determine brightness. Individual photons do not really have an “amplitude.”
If you think of light as a wave, then amplitude is the brightness.
It’s not the Planck limit, it’s that there are all sorts of other random motions that will randomly swamp the signal. Atoms vibrate at random constantly. There are millions of other sources of vibration. And so very soon you cannot extract a signal from the noise, no matter how sensitive your instrument would be.
Just like the example above, you can microwave a baked potato, but the information contained in the microwave radiation is completely destroyed in the heat. You can’t extract the signal from the hot potato.
Is that the same thing as the signal not existing?
I understand “noise” to be the mixture of all sorts of signals, so many of them that they can’t be distinguished. But that doesn’t mean that the signals aren’t there. If they weren’t there, then we’d have silence instead of noise.
What’s the difference between a signal that doesn’t exist and a signal that can’t be detected?
Heat is random vibration of atoms. Sounds destructively interfere with each other. At some point the signal no longer exists, not due to limitations in the detector, but due to limitations in the laws of physics. You can’t drop a drop of ink into a glass of water and shake it up and then a day later detect where in the glass the ink was dropped, because the signal is gone.
And to clarify for Keeve - this does not mean can’t be detected due to technological limitations, it means can’t be detected even in principle.
Deep space contains about one atom per cubic meter. There is nothing to bump against, hence no sound of any kind.
The Bohr radius of hydrogen is 5.29E-11 meters, which is a volume of 6.1977692e-31 cubic meters.
If each atom in deep space was the size of a basketball, its closest adjacent atom would be 1.39 million miles away. If there was one basketball floating in space every 1.39 million miles, what are the chances of them ever hitting each other?
It would not be zero.
I think Keeve thinks “signal” means motion of any kind whatsoever caused by something bumping into something else. It doesn’t – it’s more than that. It means enough things bumping into enough other things in a coherent enough pattern (spatially and/or temporally) that some kind of information exists. It’s not slam dancing; it’s groovin’ like you mean it.