Why does light even move? what force makes it move at insane speed?
In: 193
A light analogy that keeps my brain happy is imagining a table of billiard balls all touching one another. An impulse one side causes an almost instantaneous reaction the other – the time between the cause and effect being a function of the physical characteristics of the medium and being a constant
You’ve got a lot of answers to the light-specific part of the question, but a comment on the second part of the question:
Movement doesn’t require force. Only a *change* in movement requires force.
You’re used to associating movement with force because we live an environment that always has things slowing us down. If you’re moving along the ground, you have friction. If you are moving through the air, you have air resistance. So you need a constant force pushing you forward, in order to cancel the forces slowing you down.
If you’re out in empty space and you are flying along, you don’t have or need any force to keep moving.
There are lots of “fast” things that aren’t light, e.g. solar neutrinos that have mass, but move at *nearly* (not quite) light-speed (by our reference frame). They don’t need an active or ongoing “force” to keep moving. They just do that forever until they hit something.
If it doesn’t move that fast, it wouldn’t be called light. Light is actually part of something bigger that can move at various speeds (and can even decay very quickly). The component that move fastest is called light. You just don’t see the other components normally, because if it moves slower it has mass, and when it has mass it decay in strength, and in fact it decays so much that its range of movement is effectively less than the size of a proton.
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.
Nothing. Nothing makes light move that fast. Literally.
Light as almost 0 mass. Which means its not *slowed down* much (if any). Everything is in motion. Everything is moving. There’s no force behind this motion it’s just the state of things. Mass makes things move slower the more of it a given thing has.
Also, nothing moves. Literally.
This is part of that whole thing Einstein came up with that everyone knows of, but basically no one knows what it means. Space and time are the same thing. To move in space is to move in time, to move in time is to move in space.
Time and motion are also 100% relative. To everything. All the time.
No. Relay.
If you were moving at almost the speed of light, time would seem to stop for you, and consequently, motion would seem to stop. From your pov. From our PoV you’d basically just teleport away.
Fun fact, no pov is correct. All of them are right at all times, always. Does that make any sense? Nope! But it’s how this 8th grade shop class birdhouse of a universe is set up.
What’s this mean? It means a lot of our ideas about how things work are only true from our reference frame (science talk for PoV) on this dirt ball we call Earth. If you were moving just under the speed of light away from the center of our galaxy, and you were passed by someone moving at the same speed as you but in the opposite direction, they would appear to be moving faster than light from your reference frame, and all observations and measurements you could make would also say they were moving faster than light.
TLDR; Speed, motion, distance, and time are illusory effects created by the 3 spacial and 1 temporal dimensions of spacetime, and consequently what we know of them is only a fraction of their true nature.
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.
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
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