Radio wave and light wave are the same thing. They all are electromagnetic radiation, the only difference between them is frequency. My question : 1, is there any photon-like thing for radio wave? 2, how far can they travel in vacuum space?
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$\begingroup$ all electromagnetic radiation is composed out of superposition of photons en.wikipedia.org/wiki/… $\endgroup$– anna vJun 28, 2019 at 15:08
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2 Answers
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Radio waves are like other frequency E&M radiation in that they can travel infinitely far in a vacuum at the speed c. c = 2.998x10^8 m/sec. Photons can have the frequency associated with the radio frequency.
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Radio waves are just a less energetic version of infra red or visible light, so like the other wavelengths they have a particle aspect (photons) as well as a wave aspect. Nobody really understands wave/particle duality, you can only see whichever aspect your equipment is designed to detect. As to how far they can travel in a vacuum, the electromagnetic force reaches to infinity. Radio waves are part of the electromagnetic spectrum, so the answer is any distance you care to mention. I think the furthest yet detected by radio telescopes have travelled nearly 14 billion miles. Bear in mind that at distances of billions of miles, photons become red-shifted due to the expansion of the universe, so may not have started out as radio waves. Other factors such as gravity can also red shift them. Space is not a perfect vacuum, which doesn't make much difference for distances of under a billion miles, but probably does for distances far greater than that.
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$\begingroup$ PS The classic example of waves behaving like particles is the photo electric effect, where high energy photons knock electrons out of a metal plate, but radio waves are far too weak to do anything like that. Einstein's Nobel Prize was for his 1905 paper on the photoelectric effect. $\endgroup$ Jun 28, 2019 at 15:52
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$\begingroup$ OTOH, radio waves can make the electrons in a piece of metal wiggle around. If they couldn't do that, radios wouldn't work. $\endgroup$– PM 2RingJun 28, 2019 at 22:35
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$\begingroup$ Where does that figure of 14 billion miles come from? That's not very far, around 150 AU. $\endgroup$– PM 2RingJun 28, 2019 at 22:38
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$\begingroup$ To the best of my knowledge, no telescope or radio telescope has detected electromagnetic waves from more than 13.8 billion miles away; if they have, they certainly haven't trumpeted the fact. $\endgroup$ Jun 29, 2019 at 8:41
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$\begingroup$ Space is not an absolute vacuum. When photon travels, it must hit some particals and becomes less energetic. This leads to red-shift. If phonon travels too far, the red-shift must be enormous. And the phonon will disappear finally. $\endgroup$– Cang YeJun 29, 2019 at 13:39
