Eli5: Why does light travel so fast?
In: 130
It’s because light has no mass.
Think of something really heavy. A push and it will move, but slowly. Now take something lighter. Give it the same push and it goes faster than the heavy thing. Now push something with no mass at all and ALL of the push goes instantly to the fastest speed the universe can handle; that’s the speed of light. Push any harder and instead of going faster, it changes color because it literally CAN’T take any more energy as speed, so it turns it into higher frequency (so a different color).
The real question is why does light travel so slow.
Light always travels as fast as it can. It just turns out that “as fast as it can” in a vacuum puts it right up at the natural speed limit of the universe, the speed of causality. So the speed of light is not actually the speed of light. It’s the speed of causality.
The real question is “why is the speed of causality a thing.” And the answer, unfortunately, is we have no idea.
We don’t know how fast light travels, we only know how fast it travels on a round trip.
Einstein left it as a open question. If you can actually prove it: Bravo. If you disprove it: Bravo, you have a lot of work before you.
You know the equation Force = mass x acceleration? That can be rearranged into Force / mass = acceleration.
Light has zero mass, so to find it’s acceleration we would have to calculate the forces acting on it divided by zero.
(Force / 0 = acceleration)
Theoretically, anything divided by zero is infinity. That means any force applied to light would immediately give it infinite acceleration, and therefore infinite speed.
(Any number / 0 = infinity)
But the universe puts it’s own speed limit on every object in existence for some reason (including light particles) so it caps at 300,000 km/s.
Actually, e=mc squared is not the complete formula. Rest mass is also a factor. https://www.britannica.com/video/185388/equation-theory-energy-relativity-mc
Light travels extremely slowly, relative to the scale of the universe. It only seems fast to us because we’re a tiny ant colony living on a speck of dust floating in space.
It takes over 4 years, at the fastest possible speed that anything can travel in our universe, to get to the nearest star to our solar system, Proxima Centauri. A round trip, assuming you had infinite energy to spend and could survive infinite g forces, could never be accomplished in less than about 8.5 years. By anything, not only spaceships but also light and information. And that’s just to get to the nearest star, in a galaxy full of hundreds of billions of stars.
If humanity is never able to figure out a way to travel faster than light, then it’s unlikely that humanity will ever spread to any significant distance, and almost certainly will never leave the milky way galaxy, even assuming that we avoid killing ourselves and manage to survive for millions of years into the future. It takes light over 100,000 years to cross the milky way galaxy from end to end. And that’s just our dinky little galaxy. There are trillions of other galaxies in the universe that we can see, and on average it takes about a million years for light to travel from one galaxy to the next nearest galaxy.
Light seems fast to us, but on the scale of the universe, it is stupidly slow. Whoever designed the simulation we’re in really didn’t want us to travel too far away from home.
Science cannot answer “why?” questions. It is very good at describing how things behave but can’t determine why that behavior exists.
Measurements can capture the behavior of light, and that behavior can be described with the same geometric analysis that describes bending and curvature of surfaces but finding the curving-surface equations to be useful in predicting the behavior of light does not make the curvature exist, just as finding the equations defining kinetic energy doesn’t make kinetic energy exist beyond the usefulness of the equations as an organizing principle for observations of the physical world.
In the same way, alphabetical order does not exist except as an organizing principle for a list of words. When you try to isolate and indicate “alphabetical order” you find that there is nothing there except the relationship of one word to anther under the criterion of an arbitrary pre-arrangement of a set letters.
[Everything](https://i.stack.imgur.com/4xBUV.gif) moves though spacetime at c, that is the speed of causality. It’s just that all the massive things(electrons, protons, people, planets etc) move some in direction of time, light moves only in spatial directions and doesn’t experience time. That’s why a photon can just continue going from big bang up until the heat death of the universe, it can’t decay, because it doesn’t even move in time direction.
Would it be fair to think about it the other way around? For light, that is weightless, it travels at a speed that means it doesnt experience time since it stands still in their relative frame of reference. Ie light always travels instantaneously. Its the rest of us who are slowed down to some degree by being massfull, like being in a giant pool of mud that encumbers everything else to some degree away from “instant”?
As a thumb rule, things tend to be faster when they are running away from something, rather than when they are running towards something.
Based on this, we can assume that light travels so fast because there is something it is running away from.
We don’t know what.
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