Eli5: Why does light travel so fast?
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While there is no direct answer to your question of “why”, there is an interesting relationship between fundamental constants of the universe and the speed of light.
Light is an electromagnetic wave. That means that it is composed of electric and magnetic fields, whose oscillation directions are mutually perpendicular. There are two fundamental constants of the universe that govern, if you will, how easily magnetic and electric fields can oscillate in a vacuum. Those are the vacuum permittivity (ε0) and permeability (μ0). It turns out, not too surprisingly, that the speed of light can be equated from those two constants as
c=1/√(ε0μ0)
You could therefore say that light travels in a vacuum at the speed it must travel, given the fundamental structure of our universe.
μ0 and ε0 are actually defined in terms of c, not the other way around, but I have always found the relationship intriguing.
This can’t be answered.
I could explain to you some of the mechanics involved, but the ELI5 version is that the speed of light is a simple result of the combination of a handful of physical constants of the universe. It has to be exactly that speed and no other in our universe because of the values of those foundational numbers.
But why are they those numbers? No way to know.
When it comes to such fundamental things, I like to turn to the anthropic principle: given value could be different, but such change in circumstances wouldn’t allow us to emerge and observe it.
Sometimes why questions kind of answer themselves. I mean what is light, really? I guess it’s the thing we use to see, but ultimately that’s secondary. There was light before there was eyes.
If you ask “why are beds slept on?”, then there’s not much to say because that’s just what bed means. You could instead ask “why do we prefer to sleep on soft comfy surfaces?”, but the original question is kind of getting it backwards.
In the same way light just is the fast stuff. It going fast is practically a defining feature. It’s not the only type of fast stuff, but beds aren’t the only thing that people sleep on.
You might ask instead “why do we use the fast stuff to see the world around us”. This is simply because having an organ that can sense the fast stuff lets us find out about things as fast as possible.
Why question are difficult to answer while how question (descriptions) are relatively easy in comparation.
One explanation is that that speed is the speed of causality. A massless particle can’t disappear before being created. Depending on your reference frame it can have a different “travel” in spacetime but still you always see it the same speed, the speed of causality. No consequence can happen faster in space-time than its cause.
Although this is a more general principle that’s not really saying much about why.., why does causality had that speed value? We don’t know.
One way of thinking about it is that light has zero mass.
Neutrino’s also have almost zero mass, they are tiny, about 500,000 times less massive than an electron. They also always move at essentially the speed of light. In fact, so fast do neutrinos move, I don’t think we’ve ever measured it accurately enough to confirm they move slower than the speed of light. For a long time we weren’t sure if they had any mass or not, because they always appeared to move at the speed of light, within the precision of our ability to measure their speed. We now know that they do have a tiny mass, from other methods. I think it took 40 years after discovering neutrinos, to discover they did have non-zero mass.
If having no mass confuses you, it shouldn’t. In Quantum Field Theory, mass is just another field (the Higgs), so having no mass is really no different to having no electric charge, and thus not interacting with the Electromagnetic Field at all.
Is the blackhole real and what happens when you get sucked in?
You can flip this question on its head. Why doesn’t everything travel at the same speed as light?
Photons aren’t the only particles that travel at the speed of light. It turns out that all particles travel at the same speed except for particles that interact with the Higgs field.
The answer is that everything does travel at the same speed unless it’s prevented from doing so. Instead of solid stuff, mass can be thought of as something that takes energy to move.
More like. Why does light travel so slowly?
Fast? Given the size of the universe, light travels excruciatingly slow. The closest star to ours, Proxima Centauri, is over 4 light years away. Imagine if driving your car at top speed it took you four years to reach your nearest neighbor… Most stars within our galaxy are tens of thousands of light years away. The closest major galaxy to ours, the Andromeda Galaxy, is over two million light years away.
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