is light electromagnetic waves or is it made up of particles
and what is the “string theory”?
Light sometimes behaves as if it is made up of discrete particles (photons). These are very small and have no rest mass.
Light sometimes behaves in a “wavy” manner, for example when you see “interference” patterns.
It is not possible to observe both behaviours at the same time. Which one you see depends on what experiment you are doing.
Various “interpretations” have been put forward to explain this strangeness.
I know next to nothing about strings, except that there exists a theory that purports to explain various forces, and ultimately the particles which make up matter, in terms of “strings” or “superstrings” which are particles very much smaller than the more familiar “fundamental” particles.
I’m sure someone more helpful will be along in a minute.
thanks
but i still dont understand how the hell u can have at one moment particles and at another time waves…
there has to be either waves or particles
Light is both an electromagnetic wave and a massless particle, called a photon. It is not transforming from one to the other. Rather, it has different behaviors, depending on what it interacts with.
Particles with low rest mass (e.g. photons, electrons, etc.) can be delocalized. (They aren’t at a single, pinpoint location in space, but rather smeared out over a region.) This means they can exhibit wave-like behavior, such as interference with other particles of the same type. They aren’t “point particles” as such, but rather fuzzy blobs which can interfere in a wave-like manner.
However, there are interactions which will localize the particle. For example, collision with a particle of a different type. Because they are different particle types, they can’t interfere. Rather, they either collide or they don’t. A good example is Compton scattering, in which a photon scatters off an electron. If the two particles interact, it must be in a local, point-like way, so they scatter like billiard balls. (Incidentally, even though the photon is massless, it can have momentum. This is because the rules are slightly different at light-like speeds.)
The reasons this all works and makes sense is because of the quantum description of particles.
as hibernicus said, light is both, depending on how you look at it.
You can prove that it comes in discrete quanta beause of the photoelectric effect, in which light of a certain frequency is absorbed by electrons in a material, and frees them. The units of energy absorbed are discrete rather than continuous, so light comes in discrete packets (particles). Also, a brighter light of lesser frequency doesn’t do anything, so you know that the electrons aren’t just taking as much as they need to jump energy states, they also need it in a certain form (single photon).
On the other hand, light is waves, because you can get interference effects, and because Maxwell’s equations describe it quite nicely.
Another thing to keep in mind is that EVERYTHING is waves at some scale. Light, electrons, baseballs, you. It’s just that the wave nature only shows up on quantum scales, so we don’t usually notice it.
As for string theory, I’m ignorant.
Nor are you likely to understand, no matter how much it is explained. Nature is entirely counter-intuitive on the quantum level. It does not correspond with common sense. At some point, you just have to throw up your hands and admit it doesn’t make a bit of sense, but that’s the way the world is. Annoying, huh?
string theory in a really tiny nutshell:
the universe actually exists in 10 or 11 dimensions. the reason we think there are only “3 + time” is because the other ones are really small, really REALLY small, and exist in the form of tiny quivering loops. on a larger scale, the distribution of these dimensional threads at the beginning of the universe is believed to have affected the gathering of matter—such that where there were cosmic strings, matter would accrete, eventually turning into stars, galaxies, etc.
I’m sure you mean well, here, but I strongly disagree with this attitude. Quantum mechanics is counter-intuitive in places, to be sure, but it is by no means magical or impossible to understand. People should not assume from the outset that it is too hard for them to understand, because it is not. The math can be tricky, but the ideas are definitely accessible, if taught correctly. More importantly, they are consistent and logical, once you get past your macroscopic assumptions.
“There was a time when the newspapers said that only twelve men understood the theory of relativity. I do not believe that there ever was such a time. … On the other hand, I think it is safe to say that no one understands quantum mechanics. … Do not keep saying to yourself, if you can possibly avoid it, But how can it be like that?', because you will get down the drain’ into a blind alley from which nobody has yet escaped. Nobody knows how it can be like that.”
R. P. Feynman (1967a)
No disprespect to the brilliant Feynman, but actually I think there almost certainly was such a time. Suppose at one time only one person understood the theory of relativity - a good candidate being some chap called Einstein. Supose at some later date, more than 12 people understand it (which is the case today). At some point, then, the number must have stood at 12.
This must be true unless you want to invoke moments when lots of people all simultaneously gained their understanding of the TOR. Provided one measures by small enough fractions of a second, I think this possibility can safely be discounted.
Okay, okay! I was leaving anyway…