I don’t think this meme has anything to do with that right? It’s just a joke because we used to call all DNA that does not actively code for proteins and lies outside of genes Junk DNA.
Heh i know that those terms are a thing but the meme is saying that some person’s genome is junk/garbage/rubbish. That is just condescending with the bad taste of eugenics.
Light doesn’t travel the same speed in water or glass as in a vacuum.
In a medium, light usually does not propagate at a speed equal to c; further, different types of light wave will travel at different speeds. The speed at which the individual crests and troughs of a plane wave (a wave filling the whole space, with only one frequency) propagate is called the phase velocity vp. A physical signal with a finite extent (a pulse of light) travels at a different speed. The overall envelope of the pulse travels at the group velocity vg, and its earliest part travels at the front velocity vf.
That's light as an aggregate wave. Photons, actual light, always travel at c. What's happening in a medium is the rapid absorption and readmission of photons. The probability of admission is based on structure of material causing things like lens or mirrors to work.
You can think of it as the photons having to jump between platforms before the can continue running at c.
What’s happening in a medium is the rapid absorption and readmission of photons. […]
You can think of it as the photons having to jump between platforms before the can continue running at c.
That’s an intuitive model, but unfortunately it doesn’t have the advantage of actually being correct. Photons are not being absorbed and reemitted. See here for why: lemmy.world/comment/5444224
That is wrong. Stochastic yes. Photons emission is probabilistic. Destructive interference causes emission to overwhelming follow classical wave theory. Here's a better explanation with a neat graphic.
It sounds like you’re conflating different concepts. A stochastic process like absorption/reemission would blur the light, so that’s not it. And the linked explanation is basically correct (in classical physics at least), but it doesn’t corroborate what you originally claimed as that’s not necessarily requiring absorbing anything. Photons can jiggle the charged particles in glass and get them to make new phase shifted light despite not being absorbed.
But doesn’t relativity explicitly state that c is the speed of light in a vacuum, and travelling through other mediums explicitly changes and is explained by relativity?
Not really no. Special relativity explains the relationship between space and time. General relativity expands on this to account for gravitation.
One of the postulates (i.e. assumptions) of relativity is that the speed of light in vacuum is the same for all observers. But the theory doesn’t actually require any particular value for c, it only needs it to be constant. And it doesn’t explain the behavior of light in a medium at all.
In fact, relativity doesn’t explain the mechanism by which light interacts at all, that is the domain of Quantum Electro Dynamics.
the speed of light expressed in units of distance per time, is a dimensionful quantity so it probably doesn’t mean anything to say some theory does or does not predict a value for it. The value is entirely determined by how big you choose your yardsticks and sundials to be, which is arbitrary convention.
It is only meaningful to talk about theoretical predictions of the values of constants if they are dimensionless, like the fine structure constant.
However relativity does suggest as a natural point of view that space and time are just orthogonal directions in a unified spacetime. In this point of view, relativity gives you the option of measuring your timelike and spacelike coordinates with the same yardstick (which you may still choose arbitrarily). And then relativity does predict its value. It’s 1. No units.
Wow that is so interesting. So am I understanding that relativity explains space, time and gravity’s interactions with one another, while quantum science explains interactions with much smaller objects like matter?
Don't think about individual photons. Think about billions of them with destructive and constructive interference. The probabilities of all the sitting l additive waves of light.
well, if it get reflected and change direction it going to be at light speed, so it can be interpreted (probably incorrectly lol) that it “accelerated instantly to the other direction after the reflection”?
This is an interesting question. Instant acceleration is mathematically implausible, but I don’t know if there’s a better physical interpretation for what happens to a bouncing photon. I’m guessing this is one of those “less particle, more wave” situations where the instantaneous velocity of the photon is undefined.
According to some random internet sources, reflection is the not-quite-instantaneous process of the photon being absorbed and then emitted by the electrons in the mirror.
As a rule, it’s probably best to avoid “random” internet sources on matters of how light works because there’s so much confidently parroted misinformation out there. For example, this is completely wrong: youtu.be/FAivtXJOsiI See here for correct answers to that issue: youtu.be/CiHN0ZWE5bk
The speed of light is different depending on the medium though isn’t it? So to change speed I would have thought some acceleration would have to be involved.
science_memes
Oldest
This magazine is from a federated server and may be incomplete. Browse more on the original instance.