Why does light even move? what force makes it move at insane speed?
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It really doesn’t. It seems like it moves, to us, because we’re so massive. To it, however, it’s basically at every point of its path at the same time. Or rather – that path is stitched together into a single point.
It’s really difficult to word it in a non-ridiculous way, because explaining what it would be like if we were to travel at light speed is such a ridiculous concept.
there’s no real “force” involved. forces accelerate and decelerate things. massless particles just kind of… travel at the speed of light.
mass comes from interaction with something called the Higgs field, so you could sort of think of the Higgs field as being the thing that *prevents* things from going at *c*. things without mass don’t interact with this field, so they just… travel at *c*.
(note: light *can* travel slower depending on the material it’s travelling through, but you can’t grab it and slow it down like you could with, say, a cannonball)
Space and time are two sides of the same coin. All objects move at maximum speed, but sometimes they are moving through space fast and sometimes they are moving through time fast. The faster you travel through one the the slower you travel through the other, though the reason for why these speeds are dependent on mass is yet unknown.
Photons have zero mass, so they move through space at maximum speed, and time at does not pass for them from their vantage point. The opposite is true for black holes. These are extremely massive and time from your vantage point would just about stop the further you go to the singularity if you were to fall into it.
No force pushes the photon. Interestingly, movement at the speed of causality (the speed of light – the fastest that the universe can send signals through itself) is the default state of things in the universe – it just depends on how fast they are moving through space and of they are moving forward through time.
Edit: botched a word
Edit 2: I got something backwards, another user pointed out that time basically stops from an outside perspective for you if you travel into a black hole, not inside. What I meant to say is that from the inside time is going so slow for you but very fast for the rest of the universe that you would see billions of years or more of the future of the universe as you fell in. I think I’m getting that right.
I think it’s easier to explain if you think of light as a wave. Imagine you’re holding a rope tired to a pole and it’s stretched so that it stays horizontal. If you shake your end of the rope, you’ll make waves in the rope; you can watch the shaking move down the rope to the other side. Making light is kind of like shaking one “end” of the electromagnetic fields. The shaking will continue moving to the other end.
What makes it so fast? Imagine the rope gets heavier. The shaking will take longer to move to the other side than it did with a light rope. The speed of the waves is dependent on the rope. In the case of light, the speed of light is just dependant on the speed ripples can go through the EM field (how “heavy” the EM field is).
Fun fact: the matter the light is traveling through can change how fast the EM field ripples which actually slows down or speeds up light (light travels slower through water than air, which is part of why things look funny through a flat of water). Think of that as a rope with changing thickness… waves go faster through the lighter/thinner parts than through the heavier/thicker parts.
If you think of light as a particle, then the simplest version of the answer to this is that from our perspective photons are always made with momentum; no force has to make them move, they’re just already moving. The “insane speed” maybe makes a bit more sense if you remember that a photon is insanely light (as in, not heavy), so it doesn’t take much energy to make it go that fast.
Things get pretty trippy if you keep going with the particle view, though, because it doesn’t do a good job of explaining why photons speed up when they leave your glass of water and enter the air. If you dig into that too far, you’ll realize the answer is, essentially, that photons can only exist if they’re going at the speed of light; otherwise they don’t make any sense at all because they have no mass. Relativity is weird that way.
An object that is at rest with no mass has zero energy. ( m=0, p=0, E=0)
If there is no energy, or mass then such an object cannot exist.
Therefore, if an object exists such that it has no mass, it must have some kinetic energy so that it’s total energy is not 0. ( m=0, p≠0, E≠0). Eg: light.
Ps. If you consider light as a wave, a wave cannot exist if it’s not moving. The moment it stops moving it seizes to exist ( ie it loses all properties of a wave – time period, wavelength, frequency etc)
Short answer: it just does and no force makes it move
Longer answer:
First things first, light is probably the weirdest simple thing everyone deals with all the time, physically speaking. Light has no mass so it doesn’t need a force to propel it. It doesn’t speed up or slow down. If it exists it travels at the speed of light. It’s easier in this case to think of it as a wave, like on a string or in water. So just like nothing pushes those other waves along after they’re made in their string/water, nothing pushes that light along. They just travel in their speed set by whatever medium they’re traveling through
So, there’s a super cool set of equations governing electricity and magnetism. Light is an electromagnetic wave, so it is governed by these equations. Plug in known values for quantities like the permittivity of free space, and you can *derive* the speed of light.
Irregular Webcomic has an excellent explanation of this, here: https://www.irregularwebcomic.net/1420.html
It doesn’t really move. It does not exist on the time axis in spacetime so technically it has no speed. We perceive it that way, sorta, because causality itself does have speed. (That is actually what “c” stands for, as in speed c, referred to as the speed of light) But from light’s perspective it doesn’t move. It just arrives wherever it is aimed at the instant it is created. The universe is flat to light, doesn’t matter where it is pointed at, it will be there immediately from its perspective.
Think about it this way, you can’t actually watch light go anywhere. You can’t look at a photon and be like “woah look at that thing go”. You can only receive photons by intercepting their “path”. You can capture them but you cannot observe them, because technically they don’t exist on the way to wherever they are going. They exist only at the exact instant that they “arrive”. Once you detect a photon that means it no longer exists, it arrived. The only way to detect it is by getting hit by it. You can’t look at a light photon from the side and watch it whizz by, it’s not actually traveling through spacetime the way we intuit.
In fact, no matter *your* speed, light will always hit you at the speed of light. It’s weird like that because, again, it doesn’t have a speed in the traditional sense to begin with. Time slows down the faster you go due to time dilation. There is no time at speed c. And speed is a function of time and space, you cannot have a speed without time, which light does not have. When something has no speed it experiences maximum time. When it has no time it experiences maximum speed. Which in this case is like serious ultra maximum to the max because the speed is catching up with causality itself at that point, which is why it effectively doesn’t even have a speed anymore. It teleports. It would arrive to you the same moment the information of its existence arrives to you.
When you get to the bottom of things with general relativity and quantum physics, stuff just get real weird. Our brains are made to make sense of our immediate surroundings so that we can survive. Everything else is basically incompatible, we’re not built to compute this kind of stuff and there’s no way to develop an intuition for this natural because it doesn’t affect us in a way we can do anything with biologically speaking.
Tl;Dr – light doesn’t move at all.
Instead of thinking of it as movement, think of light spreading.
When you drop water on the floor, it “moves” at a speed consistent with the angle, mass, etc. But light doesn’t have those resisted factors like friction or air resistance..
So it spreads at an incredible speed.
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