Eli5: Why does light travel so fast?
In: 130
Light has no mass and therefore no inertia. Light is a wave that by definition moves at light speed. In a vacuum, it moves at the fastest possible speed — light speed –because there’s no inertia or obstacles to slow it down.
In a sense, there’s no answer to the question “why.” That’s just what light is. It’s an electromagnetic wave that moves as fast it is possible to travel in a vacuum.
Well, depending on your perspective on the universe, light actually travels really really slow.
It may seem fast to us, driving a car down the road and light is some unimaginably faster speed than we can go in a car, or even us flying. But the unverise is HUGE. Just our galaxy, the milky way is 52,000 light years across. Thats insane right, you thought light was fast, but just a tiny spec of the universe that is our galaxy would take light 52,000 years to traverse? Its slow as hell
If you push on something, it starts to move, right?
If you push on it 2x as hard, it starts to move 2x as fast, right? *Wrong*.
In essence, we’ve learned the thing only travels something like 1.99999999x as fast, somehow energy is going missing.
Using Einstein’s math, we learned the missing energy is somehow getting “absorbed” by the object and getting turned into mass, meaning the object doesn’t get pushed as easily as it did a moment ago, which is why it only goes 1.9999x now, not 2.
Extending this math out, and this bit gets confusing, we learn that since objects get “heavier” the faster they move, and also that they get “heavier” faster than they accelerate, if that made sense to you, it means that an object gets heavier faster than you can accelerate it, ultimately you can’t push an object any faster. It would take literally an infinite amount of energy to push the object even one teensy bit faster. So that becomes a Galactic Speed Limit, and that speed is a massive number so we just call it “C” for short.
Now all of the above only applies to physical objects, objects with Mass. No object with mass can ever travel at speed C, or faster, C is the limit.
Light though, in this context, light is pure energy and does not have mass, so it is uniquely capable of traveling at exactly C. Even light can’t go beyond C, but it can travel at C.
So it’s less accurate to call C “the speed of light” and more accurate to call it “the maximum speed possible, which only light is capable of traveling”. It’s sort of a chicken vs the egg thing.
There is a speed that is the fastest you can go. Most things have mass so can’t reach that speed without a lot of energy to move it and they can never quite reach it because of the mass.
Light has no mass. So any energy at all immediately makes it travel as fast as it is possible to go.
As far as we can tell, the universe seems to have a max speed cap on how quickly anything can affect anything else. We call that the speed of causality, or *c*.
There’s a fundamental property that some particles have and others don’t, called *mass*. You might know it as the thing that causes the sensation of weight, or makes things hard to lift or move. Whether or not a particle has mass determines how it interacts with this universal speed limit:
* If something has mass, it can travel at any speed it likes, as long as it’s less than *c*.
* If something does not have mass, it must *always* travel at *c*, all the time. No exceptions**.
^(** Assuming it’s in a vacuum)
Light happens to be massless, so it always moves at the speed *c*. This is why *c* is more typically called “the speed of light”, even though it really doesn’t have anything to do with light.
Answers to some possible followup questions:
> “Why does the universe have a max speed cap at all?”
We don’t know.
> “Why is the speed of *c* what it is?”
We don’t know.
> “Why does the universe have some particles that have mass, and some that don’t?”
We don’t know.
Light travels fast because it is an electromagnetic wave, which means that it is made up of electric and magnetic fields that can propagate through empty space. Electromagnetic waves are able to travel at a very high speed, about 299,792,458 meters per second, which is the fastest speed possible in the universe. The reason why electromagnetic waves can travel at this speed is because they are not affected by the material through which they are traveling. In other words, they can move through empty space without any resistance or interference, allowing them to travel at their maximum speed.
You can easily push a light little pebble around, but you’re not going to even budge a massive boulder, right?
* The more mass something has, the harder it is to make it move.
Then even if you *do* push the boulder, you’re gonna have to push it *even harder* to make it move *faster*.
* The faster something is moving, the more energy it takes to make it go *even faster* – and *also* the more mass it has, the more it’ll take.
Light has *no* mass, so it moves at the fastest possible speed that anything can move. Light isn’t special here, either: anything else that also has no mass will move just as quickly.
The speed is so fast because light is a type of electromagnetic radiation, and it is able to travel through a vacuum without encountering any resistance or other obstacles that would slow it down. Additionally, the speed of light is the maximum speed at which information can be transmitted in the universe, according to the theory of relativity. This means that light is able to travel extremely quickly because it is not limited by the same physical constraints that affect other forms of matter and energy.
The speed of light is the speed a massless thing *must move at* to make our reality what it is. When looked at with a cosmic perspective, the speed of light is somewhat slow, it can be overwhelmed by a black hole, bent out of shape by gravity, and it takes millennia for it to travel in interstellar space.
We can’t really answer the question very well because the best we can say is ‘there has to be a cosmic limit, and it might as well be ~299.8 million meters per second.
Light has no mass, so there’s nothing stopping it from going fast. When you make it go, it instantly goes as fast as possible.
For some reason the universe has a speed limit, so light goes at that speed. If the universe didn’t have a speed limit, light would probably be instant.
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