Speed of light in vacuum

>reacting to subjective sizes
>what is relativity

You can actually get the speed of light from the electric and magnetic constants, if you measure those accurately you can get the speed of light.

We found out its theoretical speed due to maxwell equations. While in water for example the speed of light is slower they're talking about the speed of the wave not the photon.

Google is your friend.

math.ucr.edu/home/baez/physics/Relativity/SpeedOfLight/measure_c.html

Also this, but lacks a clear explanation of how.

[math]c=\dfrac{1}{\sqrt{\mu_0 \textepsilon_0}}[/math]

>^_^

>where there is light it is not vacuum right?
the presence of any electromagnetic waves is irrelevant for the definition of a vacuum(matter-free space)

>math.ucr.edu/home/baez/physics/Relativity/SpeedOfLight/measure_c.html
>we DEFINE the speed of light to have this fixed value of 299,792.458 km/s

What the fuck? Is this the state of science these days?

I don't think you understand. The meter is defined as the distance light travels in 1/299792458 sec. The speed of light is the constant on which all measurements of distance are based. So it doesn't matter what the specific number is, as long as it is consistent.

It's unsatisfying. Why'd they pick that number, specifically? Why not a nice round number? Why that speed? How did they know to set it to that exact speed?

Interpret "vacuum" as "region in which the curvature of space time isn't distorting that path which a massless particle travels."

Because we created an entire system of measurement based around the meter before we knew how fast light travelled.

Now that we have accurate measuments of a quantity which isn't subjective for whomever is measuring it, we redefine the system's quantities around that.

No. They chose a number close to the one that was measured before. Else, they could have just set the speed at a nice round number.
I looked it up and the reason is you can calculate the speed of light from fundamental constants. So they got that number and then changed the definition but kept it the way everyone was used to it.

Turns out they are particles and waves. Likewise for matter.

Guess what that means for your head right now.

interferometer

Of course light can exist in a vacuum. A vacuum just means there is no mass. Light has no mass.

>Turns out they are particles and waves. Likewise for matter.
plz dont perpetuate this meme. thing is that in quantum mechanics you describe electromagnetic fields as something new that behaves like waves sometimes and like particles on other occasions.

it is neither.

Yes, no shit they got the number before they redefined the other quantities. The meter didn't change after it was defined in this manner, but rather its defined by something natural thing that is universally constant rather than the length of someones foot.

And do you understand the purpose of constants? Or what they are? I don't think you do.

Obviously the number will reappear with constants which deal with electromagnetic waves which necessarily travel at the speed of light....constants which have dimensions....which can be universally defined by the speed of light...

Light "is" not a particle, but it can be measured to have particle-like qualities.

We more generally look at light through quantum field theories.

Strictly speaking; the speed of light is different on earth than it is in space, due to distortions of spacetime (see relativity, particularly General Relativity theory)

Photons have a further property which is confusing as fuck; they don't "really" travel either way, but they can have traveled.

If that doesn't make sense, it's beceuse it's not an easy thing to grasp.

Photons/quants "travel" every possible path at the same time, and none.

Imagine it's like they travel a maze between two events, and once it "finds" the shortest path, that becomes the way it traveled. (forgive the abstraction here, more precisely they will be measured to have traveled the average of every possible path, including those paths where it ceases to be a photon for a while and becomes an annihilating pair of particles and anti-particles, and every possible permutation of this.)

Why ? - science doesn't tell us.
How ? - because our models, while hugely sucecsful in predicting, are fundamentally models of reality. (we use mathematics, which is a purely logically constructed language for modelling the world around us, but which still is a language. See Gödel's Incompleteness Theorem to see why I say that)

Light also has energy, but no mass, so it can't be said to be a particle. (moreover: a particle moving at the speed of light would have infinite energy, which obviously can't be allowed.)

Light is often considered a particle because it has momentum. Solar sails, and all that.

Here we see you're above average brainlet trying to describe his eloquent background of YouTube videos that he didn't understand very well. The key indication of this is the whole "not an easy thing to grasp," thing.

Light can only travel in a straight line, whether or not that is straight to an observe is dependent on the medium. This relationship is described by Special Relativity, not General Reletivity. GR is a geometrical model. SR says that in the reference frame of a massless particle, it always travels in a straight line. The curvature as described by GR will affect a massless particle's path, but only for an observer.

And since when did you need mass to become a particle? That is not the defining aspect of a particle.