As I understand it, the only real difference between radio, visible light, x-ray and everything in between is its wavelength. For instancew, radio has a very long wavelength, x-ray very short, visible in the middle somewhere. This means that radio can penetrate stuff (matter?) more effectively, among other things.
Radio waves are (essentially?) harmless, but shorter wavelengths are famously more dangerous, from sunburn all the way to straight up cancer and so forth. Why is that?
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It all comes down to the amount of energy in the photon.
If I take a bullet and throw it at you, it might sting a little bit but it is not going to do any serious damage. But if I shot you it would obviously be quite serious. The difference is the amount of kinetic energy in the bullet in each case.
Lower wavelength photons have much more energy than higher wavelength photons, so they can do more damage.
The fundamental breakpoint is if a single photon has enough energy to ionize an atom. That adds enough energy to the elections so can leave the atom. The result is molecules can break apart and/or chemical reactions can happen. The exact limit depends on what atoms you look at but it will be in the ultraviolet range.
There has to be enough energy in a single photon, you can’t ionize an atom by hitting it with two phones of half the energy.
So longer wavelengths are nonionizing and higher is ionizing radiation. https://en.wikipedia.org/wiki/Ionizing_radiation
Longer wavelengths can damage you too but it will be because they transfer energy to you and heat you up. Take a magnifying glass and concentrate visible light that is not ionizing and it can damage your skin by burning it. Consider what would happen if your hand was in a microwave that did not have the safety feature of turning off when you open the door.
So radion waves can damage you if they are enough that heat you up. A single high energy photon could on the other hand hit inizer a part of a cell and the result is a change in the DNA that is not detected and the result is cancer. It is not likely but also not impossible.
The wavelength is a function of energy. Low frequency wavelengths have low energy. High frequency radiation has high energy. So gama radiation is very high frequency. Radio waves are low frequency.
This is also the reason behind the red-blue shift. “Ultra-violet” means “more blue/purple”. EM radiation that’s more towards the red end of the spectrum is less energetic and less damaging.
It takes a certain amount of energy to break the chemical bonds in DNA. Longer wavelengths of light have lower energy photons that cant damage those bonds. X-ray photons are very high energy, when they collide with bonds in DNA they will break them and can cause mutations.
Energy of a photon depends on frequency (E=hf, h being planck’s constant)
Higher frequencies have shorter wavelengths (c=λf, c being the speed of light and lambda being wavelength)
Therefore, we also have E=hc/λ
When a wavelength is short enough (frequency is high enough), the individual photon has enough energy to break chemical bonds and knock electrons off of atoms. This is called ionizing radiation because it has enough energy to ionize. This is what makes certain wavelengths of EM radiation dangerous (starting around UVB and up, UVA, visible light, infrared, microwaves, and radio are all perfectly safe, the worst they can do is burn you if the intensity (number of photons) is high enough.
A photon’s wavelength is inversely proportional to its frequency/energy. In other words, shorter wavelengths = more energy.
Energetic photons are dangerous to life because life relies on a vast ecosystem of delicate chemical compounds, which are held together by electromagnetic bonds between atoms. Photons impart electromagnetic energy, and too much of that energy will break these bonds. This can damage all manner of tissue in a living thing, most notably its DNA. If the DNA damage is extensive enough, that can lead to cancer or organ failure as cells can no longer properly replicate and replace themselves.
You are already familiar with different types of EM radiation interacting with some things but not with others. Light can travel through air, glass, but not humans, wood or any other solid objects or certain liquids. You also can see light partially interact with things, like water only letting light penetrate so far and absorbing different wavelengths (seen as colors) at different rates.
The same is true for all of EM radiation. Radio waves can partially pass through building materials and travel long distances through air. X-rays travel mostly through tissue, but not through bone.
The reason why EM radiation reacts with certain things and not others is *quant*um mechanics and chemistry. Energy (like a photon of EM radiation) comes in packets of discrete value/size/*quant*ity. Meanwhile, every bit of matter is at some energy state or level *and* every bit of matter has a whole range of energy states it can be at, but it can’t be just *any* level. The energy states for matter are also *quant*ized.
You can picture this like a step on a set of stairs and we can label them sequentially – let’s use the alphabet, A to Z. If something is at energy level A, it takes a certain amount to get up to Step B. It’s measurable. A specific *quant*ity. And each step is slightly different than the last. Generally, the ‘distance’ of those steps get smaller at higher energy states.
For something to absorb or interact with energy (EM radiation), that packet of energy has to take you from one step to another – there are no half steps. It can be from Step A to Step B, or Step F to Step G, or from Step C to Step Q. This is pure absorption of that energy. If the incoming energy doesn’t match an energy step, then that energy doesn’t interact with the matter and passes through.
Light is an EM wave. It’s energy is proportional to its wavelength. And so thats all we need to care about.
Lets start with something called Compton scattering. We look at a free electron (free in that it isn’t bounded to an atom) and light comes around. The electron is negatively charged so it changes the EM filed around itself and this will affect light. Mathematically we can instead treat both light and the electron as little balls that collide. Calculate their momenta and see how light is deflected. The surprising thing is that the scattered light loses energy, it moves the electron. More energy, bigger kick.
We often model an atom’s electrons as they are bound to the nucleus with springs. We call this a harmonic potential, system with that tend to sit in some potential valley. If you kick them a bit they’ll return to their original state. Like a ball in a bowl. Electrons in their orbitals can be modeled much the same way. So lets play with the analogy:
If light comes around and scatters from this spring attached electron it will make it oscillate a bit. There are a lot of ways model whats going on. You can use the E field component of the EM wave and see how it moves the charges in the atom but this ball model works well for what we are interested in. There is same critical kick the electron can get above which it’ll leave the atom and fly off to infinity. If your light has enough energy for that, to knock electron from their orbitals we call that ionising radiation.
Why is that bad for us? Our cells are made of proteins, complex molecules. And if we knock electrons from their orbitals we break the bonds that keep molecules together. So proteins break down, if too much the cell just dies. But proteins are always made by the cell from a blueprint we call DNA. That is another complex collection of molecules and that can get damaged much the same way. So the cell won’t be able to produce the right proteins and dies. Or its slightly altered but still function just not cooperating with other cells. If this useless cell starts coping itself it’ll grow into a tumor. Our immune system does a good job at getting rid of tumors but occasionally it’ll fail and the tumor can graduate into being cancer. If too much DNA is damaged in too many cells these cells and their copies won’t be functional and now we are talking organ damage on a cellular level. This is decomposition. If new health cells don’t form you decompose. This condition is acute radiation poisoning. The mechanism that ends up killing you is similar to getting shot to cheese. It’s just that bullets damage your organs on macroscopic scales. If some vital organ get too many holes it’ll stop functioning and you die. Accompanied by internal bleeding, it’s just that bullets mechanically tear holes into you blood vessels while the decomposition allows for holes to form on your blood vessels.
So the cause of death after radiation poisoning is organ damage and internal bleeding. And the reason is you accumulating so much DNA damage as radiation breaks your molecules that cells stop functioning and you don’t have enough healthy cells to replace all the faulty ones.
Radio/light/x-ray/gamma-ray is all made up out of the same thing: photons.
The photons differ in only one way that matters for this, their wavelength/frequency/energy.
Wavelength, frequency and energy may all appear to measure different things but they are all the same thing as far as photons are concerned. If you know the wavelength of a photon you also know its frequency and how much energy it carries.
The shorter the wavelength the more energy each individual photon carries.
Each individual photon has a set amount of energy that it carries that corresponds to its wavelength.
Blue photons carry more energy than red ones for example.
You can make up for that by simply sending more photons of course.
If a photon carries half as much energy you can send twice as many photons and end up transferring the same amount of energy.
This is true for most things. But for some things the individual photon matters.
When a photon with enough energy hits a molecule or atom it might be able to knock an electron out of it. There is a hard minimum limit for that and you can’t get the same effect by hitting and atom wit two smaller photons as with one big one.
This knocking out an electron is called ionization.
Radiation where the photons have enough energy to do that is called ionizing radiation.
Because removing the electron means that the atom that remains is missing an electron and now charged.
Charge molecules want to get back to neutral again and may end up stealing an electron from some other nearby molecule.
Since electrons are what keeps atoms together in molecules this ionization will mess up with molecules and their chemistry.
The building plan of our bodies DNA, is a giant molecule.
Shooting ionizing radiation at it or having it be exposed to ions is like shooting a gun at a blueprint for a house.
Most of the times the holes you cause won’t matter much and there are all sorts of fail-saves and redundancies to keep your body from building stuff from corrupt plans, but if you shoot enough holes at enough plans for long enough you may end up getting unlucky and end up with a situation where the plan is damaged in such a way that your body ends up build cancer cells instead of healthy ones. This can be bad for your health.
Of course this does not mean that photons with lower energy are completely harmless.
For example microwaves are not ionizing, but they can hit water molecules just right to heat them up. since humans are mostly made up out of water and die if they are cooked. Being microwaved can be quite bad for you.
Also if you are hit with enough photons at once it doesn’t really matter whether they are ionizing or what wavelength they are.
The wavelength and energy of a photon are directly proportional – if you know one you can compute the other. The dangerous part to life is when a photon has enough energy to knock an electron off of an atom. We call this “ionizing” radiation as it makes an otherwise neutral atom have a charge, an ion. This makes the atom want to get a new electron, and it can do so by effectively “stealing” it from another atom. In a chemical, this can cause it to break in ways that make it no longer function as intended.
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