How do does radio signal keep on travelling in space? Shouldn’t it just fade away.
In: Engineering
It does fade away following the square cube law. So when it’s gone twice as far, it is one quarter as strong. Plus some losses to dust or gas blocking the signal on the way.
radio signals are just light that we can’t see with our eyes. So if you can see a star from wherever you are, you could (theoretically) detect a radio signal. The issue becomes distinguishing the radio signal from the many other sources of noise, just like it might be harder and harder to detect a faint light if the ambient light increases.
Radio and light waves are technically the same, and they behave identically on the science level, the only difference is that we can actually see one. Radio waves just pass though most objects, unlike light, those waves just see the world made out only glass
This allows us to do experiments using something *we can understand by observing it.*
If you have a light bulb, you can see it emitting light, and it is clearly visible. If you stand 10 meter away, you can probably still see it, but as you walk further away, it gets more and more dim compared to the surroundings. This is just like radio waves.
To compensate, we could use a bigger light bulb, that pumps more watts into the air, and we see it from further, [we clearly see a light house from a distance](https://www.youtube.com/watch?v=xxX36GEAJn4), but not a small AAA battery powered torch.
There is a standard for this called “signal to noise ratio”, which basically tells us how bright the wanted light is from what we want to see.
Eventually, going brighter and brighter doesn’t work, you cannot put a 1MW nuclear reactor on a small space ship. Other things are used. See it like putting a reflector behind the light bulb, to shine more light into the wanted direction, this allows a bigger distance. An extreme example of this is a laser. Compared to your light bulb, a laser light seems weak, [but over long distances](https://youtu.be/iEiOLGEO_KM?t=25), it suddenly becomes the brightest light source
We could also increase the receiver size, which allows us to better isolate the noise from the signal. We use big receivers to receive the signals from the Voyager space probes.
**TLDR**: The signal fades away, but we have ways to pick it up by increasing transmit power, or better receivers
There’s very little to impede an electromagnetic wave in the vacuum of space, but what *does* cause some “fade” is the [Inverse Square Law](https://en.m.wikipedia.org/wiki/Inverse-square_law).
Basically, no matter how focused you make a signal, the beam will spread out, and as it does, the original power is spread out over that whole surface area.
You can demonstrate this with a laser pointer. If you shine it on the wall in front of you, it’ll be a tightly organized dot. But shine it down the street and the dot will be several inches across.
*Disclaimer* if you want to experiment, be careful where you shine a laser pointer, certainly not towards any kind of aircraft.
It’s because it travels through electromagnetic waves that permeates the universe, it’s not like sound waves that need a physical interaction to travel from one place to another.
But, you are on the right track, because on larger distances other electromagnetic sources interfere with the original signal and they tend to “wash up” instead of keeping the initial properties of the signal
Yes, it fades. Whether you can detect that or not really depends on if you have the equipment to detect it at that level
Waves can be detected in one of a few ways; they either/or
* interact with existing particles in their environment. Sound is an example, requiring some sort of medium (in most cases, air/water) to continue.
* are a result of outputting particles at specific intesities (amplitudes) or intervals (frequencies). Light, for instance, is the particle itself.
Because the particles exist as their own medium, they can travel through space, and because space has relatively low amounts of other particles, they can travel without interference for the most part.
What is there to fade it? On earth the atmosphere interferes, so the waves don’t reach very far, but in space there’s nothing.
That’s not to say there’s no fading. The source can only emit a given amount of radiation. This intensity lowers the farther you go.
For an analogy, imagine a huge [bicycle wheel](https://cdn1.vectorstock.com/i/1000×1000/93/05/bicycle-wheel-vector-4419305.jpg) with spokes. At the centre, the spokes might occupy all the directions, but at a distance, the spokes only occupy certain areas of the edge. That “frequency of spokes per length of edge of wheel” is analogous to “the intensity of waves per unit area”. Nowhere is the middles the spokes change.
Astronomer here, there is a signal from the early part of the universe (13 billion years ago) called the cosmic microwave background.
If you were around even a billion years after the signal/imprint was formed, you would see it as more likely the cosmic x-ray or cosmic gamma-ray background. But due to the expansion and accelerated expansion of the universe, the light has redshifted so much it’s wavelength is now in the microwave bands (which is effectively a radio signal).
Light fades via redshifting, aka the wavelength increasing in size as the universe itself increases in size. This is why the most distant stars look redder to us than the closest stars. And stars/any light moving towards us look bluer.
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