How Radio Waves Actually Work
Radio waves are a type of electromagnetic radiation, which means they are made up of electricity and magnetism. This makes them different from things like sound waves, which are just vibrations in air (or other materials).
Radio waves are made by electrons moving back and forth. When the electrons move, they make a magnetic field. And when the magnetic field moves, it makes an electric field. These two fields are perpendicular to each other (at right angles) and they travel together through space as a wave.
The strength of the wave is related to the strength of the electric and magnetic fields. The stronger the fields, the more energy the wave has.
Radio waves have a very wide range of frequencies. The lowest frequency radio waves are like the ones used in AM radio broadcasting. These waves are thousands of times bigger than the highest frequency radio waves, which are used for things like cell phones and satellite TV.
Do Radio Waves Travel at The Speed of Light?
All the different types of waves in the electromagnetic spectrum – including radio waves, microwaves, infrared light, visible light, ultraviolet radiation and gamma rays–can be simply referred to as “light.”
The speed of light is a universal constant, and we know this from countless observations and experiments.
Radio waves, like all electromagnetic waves, propagate at the speed of light. The speed of light in a vacuum is 299,792,458 m/s; this value is often rounded to 186,000 miles per second.
Maybe a better term for the speed of light should be the speed of electromagnetic radiation, though that doesn’t roll off the tongue quite as well.
Are Radio Waves Affected by Gravity?
Yes, gravity will affect radio waves for large mass interstellar objects like stars and black holes but on earth the affect is next to nothing. This is because earths gravity is extremely small in comparison.
Radio waves are a type of electromagnetic radiation, which also includes microwaves, infrared light, visible light, ultraviolet light, X-rays, and gamma rays. These types of radiation are all made up of photons – particles that have no mass but carry energy.
Since radio waves always travel at the speed of light, their velocity will remain unchanged as they escape Earth’s gravitational pull. Instead of experiencing a decrease in speed, they will gradually lose energy due to gravitational redshift.
Radio waves will continue in a straight line more or less until absorbed or reflected off another object.
General Relativity Explains Gravity’s Effect on Electromagnetic Waves
Einstein’s General Relativity explains how the gravitational effect of curved space-time on particles that are moving works.
Radio waves are affected by gravity the same way as light is affected – the only difference is, light is visible to us.
According to General Relativity, gravity will affect light in these two ways:
The bending of light, also known as gravitational lensing. Gravity bends space time, causing a curvature that light or radio waves in this instance to follow. From the lights perspective, it’s still traveling in a straight line but observers will see the light bend.
So when light/radio waves passes close to say a star, it will appear deflected from its original trajectory.
From a distance, the blockhole’s gravity has only a miniscule effect on radio waves, but as it gets closer, the force will begin to deflect it. If it continues to get pulled in close enough, it will be forced into orbit around the black hole. And if gets too close – pull beyond what even light can escape – then eventually over time it will cross the event horizon and be trapped inside the singularity.
It will also alter the energy of light by changing the frequency of the light (gravitational redshift/blueshift).
Light moving away from a gravitational field loses energy, while light approaching a gravitational field gains energy. However, this doesn’t affect the speed of light.
As the radio wave gains energy, its observed wavelength will be shortened (the frequency will be increased) or gravitationally ‘blueshifted’.
Do Radio Waves Get Weaker in Space?
All wavelengths of electromagnetic radiation(radio waves) abide by the inverse-square law.
Double the distance traveled and you get 1/4 the signal strength, triple the distance and you get 1/9 the signal strength and so on. Remember, all the individual photons aren’t getting weaker, they are just getting more spread out.
Even lasers, which are not perfectly linear, spread out to several miles by the time they reach the moon.
This will mean that, at some point, any signal becomes indistinguishable from the background noise of the universe. The distance at which this occurs, however, is determined by the strength of the signal to begin with.
Can Radio Waves Travel Forever in Space?
Yes, radio waves would travel forever in space or a vacuum.
Radio waves are similar to light waves in that they are both “electromagnetic waves” – transported by photons. You go from visible light, red light, infrared light microwaves, millimeter waves, and then you’re into radio waves…all of it is exactly the same thing.
The Hubble Space Telescope detected light from an object 9 billion light years away – and radio waves can travel just as far.
Over those extreme distances, three things happen to both light and radio waves:
They will become increasingly faint/dim. Remember that the brightness/strength will be reduced by a factor of four each time the distance is doubled.
Because space is expanding, there is also “red-shift” to consider. Distant objects have the wavelength of their light stretched as space stretches.
Additionally, because space is always expanding, there is a continuous “red-shift” to consider. As space stretches, the wavelength of light for distant objects also gets longer.
Something that already has a very long wavelength (radio waves) grows even longer in wavelength.
So, for example:
A distant star that is 9 billion light-years away (twice as far as Alpha Centauri, the farthest object ever observed using a telescope) will be 4 quadrillion times dimmer than Alpha Centauri!
Radio waves would be 4 quadrillion times weaker for the exact same reason.
Though radio waves technically travel forever, they eventually become too difficult to detect and the signal strength gets too low to register with normal electronic devices.