I usually see myself as being pretty solid on my general science knowledge, but this one continues to stump me.
Light is photons, little particles that move through space… but then it’s also a wave, like the visible light portion of the electromagnetic spectrum? How can it be both? How would photons red shift over great distances? Do we just not know what light is, really?
In: 9
It’s less like “little particles” and more like [little packets of wave](https://en.wikipedia.org/wiki/File:Wave_packet_(no_dispersion).gif) that on the whole can exhibit some particle properties. But also retaining their wave properties like being doppler-shifted.
As far as we know, we know what it is. It’s just weird.
The quantum level was always something I found difficult at uni but it does explain alot of real world observations. However the whole entanglement stuff….is so much harder!
The mind blowing part is that when electrons are fired ONE AT A TIME through the double slit experiment, they still produce the classic wave like interference pattern
This should be an impossible result of firing a single particle through one of two slits. There’s is nothing to interfere with. The wave pattern is the result of two waves interfering… Yet one single particle “interferes with itself”.
That is where things get really difficult to comprehend because you have to think of the light as neither wave or particle.. it is just the potential to be either. It is the only logical conclusion
This is proof of the wave particle duality, and that it’s actually not a case of just not knowing what it is. Light behaves as both
It’s pretty much proven magic lol – we know what we see, but nobody knows why. [This](https://youtu.be/ISdBAf-ysI0?t=1413) documentary probably explains things more clearly if you’re interested.
Think of a solid cylinder: if you look at it end-on it looks like a circle, and if you look at it from the side it looks like a rectangle, but a cylinder is neither, it just resembles them under certain circumstances. Similarly, rather than thinking of photons as either waves or particles, think of them as something else entirely which just has some particle-like behavior when you look at it one way, and some wave-like behavior when you look at it a different way.
Red-shifting happens because the universe is expanding—the space through which the photon is traveling is stretching. Imagine you’re walking at your usual pace, only the ground beneath you is continually stretching. As you swing your leg forward to take a next step, the stretching of the ground pulls your rear foot further back, causing you to step a longer distance each time. Now imagine the length of your steps is the wavelength of a photon being red-shifted.
We know a whole lot about light, like each photon is made up of an electric field and a magnetic field oscillating in unison, but at 90^o to each other; that all photons are created as the energy shed by electrons “jumping” to lower-energy orbitals around atomic nuclei; that photons do not obey the Pauli exclusion principle, meaning two or more photons can occupy the same locale and energy level simultaneously; we know they have zero rest mass; and we know their speed, c, is defined by two physical constants: the [vacuum permittivity](https://en.wikipedia.org/wiki/Vacuum_permittivity) and the [vacuum permeability](https://en.wikipedia.org/wiki/Vacuum_permeability) of free space. However, there’s likely a whole lot we have yet to learn about light.
Think of individual particle as just a small part of the field.
Its got an electric and magnetic component.
An increase in electric field drives an increase in magnetic field and thats how it travels.
First, you need to define what a particle is and what a wave is in context on quantum physics. Vague definitions bring confusion
It’s not.
Light is light. It’s some weird thing that we don’t really have any equivalent to in normal human experience. It’s not a wave and it’s not a particle.
However, in some cases, it appears to have similar properties to a particle, and other times similar properties to a wave. This led to it being described in some cases as particle-like or wave-like.
There is a parable about three blind people describing an elephant by feel–one claims it is a snake, one a tree, and one a rope. None of these are the elephant, but the elephant–in some areas–is snake-like, tree-like, or rope-like. This is similar to light.
As humans, we like to draw parallels to common experiences and relate things to our daily perceptions. We describe like-poled magnets as “having something between them”. But that is just a description of a particular result, not a statement of being. Quantum behavior is very, very foreign, and so almost any metaphor or parallel to everyday life will be imperfect at best.
First off, photons are always waves. Particles are essentially very narrow yet very high waves: a “spike”. This wave is not just an electromagnetic one, but also one of probability, the probability where it actually is. A particle is a thing whose position is pretty much known, while a wider wave has a lot of unknown uncertainty about location.
At the smallest level of reality, the realm of _Quantum physics_, everything is a kind of wave. Measuring or interacting (those two are actually the same thing) restricts the possibilities of where things might be, and with what chance. But unlike the everyday experience of _object permanence_, this is truly not a defined position; every position has a certain chance waiting to becoming more or less likely.
At macroscopic levels and many many atoms, those chances just average out, making the position of a rock all but completely certain. Hence why we do not observe rocks as probability “clouds”. This, and that looking at the rock would already mean that we determined its position.
The best explanation I can think of is: light is a particle, but particles act like waves.
Particles (not just photons, but also bigger particles such as electrons, protons, whole atoms, and bigger things still) act like waves in the following senses:
* they can have interference patterns – such as in the double-slit experiment, which still shows an interference pattern even when you send the particles in one by one.
* they can have a well-defined wavelength, that depends on their mass and speed
* they don’t have a perfectly well-defined location
* their motion can be described by a kind of “wave equation”.
You might be thinking “hey, that baseball I threw didn’t act like a wave!” the thing is, the baseball is such a massive object that its wavelength is too tiny to detect anything wavelike about the way it moves. Waves with tiny wavelengths act like particles, after all: they travel in straight lines, reflect off things, get blocked by things, and so on.
This is one of the biggest science questions stumping everyone. If you could actually ELI5 you’d be a shoo-in for a Nobel Prize
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