Came back to this site. Clicked first article. Saw first Comment. Remember why I stopped coming to this site.

Except that cosmological redshift is caused by the expansion of the local space you are traveling through, while you are traveling through it.

The doppler shift you are referring to is the one that arises from special relativity, where you assume that spacetime is "flat" everywhere. You only take into account the motion of the source/destination, and not the effect of the spacetime between them.

Take it up with Einstein, yo.

What are you talking about? Planck-Einstein relation: Photon Energy = Planck's constant * Frequency.

If frequency goes down (more red), energy goes down. Nothing about shape. This is not a blackbody curve. We are talking about individual photons.

It sounds like you're saying the speed of light is changing? That is the one thing that relativity does not allow. The fact that the speed of light is invariant to any observer in any reference frame is WHY you get weird effects like this.

That's even true when you're not in a vacuum. The whole "light slows down in matter" thing is a simplification, and is not physically what happens.

So no, it is not the same at all.

As I said, this has nothing to do with photons interacting with matter. This result comes purely from the math of the Planck-Einstein relation and relativistic Doppler shift. You can assume an empty universe with a single photon moving through expanding space, you get the same result.

I think it's one of those things we actually don't fully understand.

However we know that the expansion is not caused by the photons, but by Dark Energy. We don't know what Dark Energy is either, of course. We just know that the expansion of space is accelerating, for some reason. If photons were causing the expansion, we would expect brighter parts of the universe to be expanding away from us faster, which is not the case.

The thing is that relativity solves these paradoxes by forcing the speed of light to be the same in every reference frame. Whatever else needs to change to make that happen, does.

Actually this is my second degree. I've also been an Electrical Engineer for 10 years, self employed as a consultant for the past 5 or so. I've paid taxes for at least the past 14. But thanks for playing! :D

I was able to transfer credits into my astro degree for the math courses and some of the intro science courses, as well as electives. So I was able to keep working part time while taking only 2-3 courses a semester (except one semester I had to take 5) and completing in 3 years.

I just completed a degree in Astrophysics, and in my last semester we took Relativity. We obviously cover relativity in a lot of different courses but this was an entire course dedicated to it. It was super cool, we covered tensors, the Einstein field equations, black holes, white holes, parallel universes, all kinds of stuff.

Interestingly, it turns out that the Laws of Thermodynamics actually don't work once you incorporate relativity. They aren't actually "Universal" at all, but only locally true within a particular reference frame.

Redshift, for example, which is due to the stretching of spacetime as light travels through it, violates Conservation of Energy. As a single photon is redshifted, its frequency decreases. From the Planck-Einstein relation (E = hf) the energy of a photon is proportional to its frequency. Hence a photon which has been redshifted arrives at its destination with less energy than it left the source with.

Photons are discrete so they cannot be "split" unless they are absorbed and re-emitted by interacting with some matter. Where did the energy go? The answer is that it goes nowhere, it is simply "lost".

Interesting stuff, huh? Completely irrelevant of course, but then again look what I'm replying to.

Do you happen to own a dictionary by any chance? Look up the word "universal", if you don't mind, and tell me what it says. Thanks!

Hoarding wealth is immoral. So yeah, rich = evil. Even Jesus Christ supposedly said so.

There are only 2 possible reasons you hold this opinion: either you're rich and a selfish fuckwit, or you're poor and a stupid fuckwit.

Ok Boomer. :)

OK Boomer.

Marie Curie once discovered that Radium could be extracted from an otherwise useless rock. Literal tons of this useless rock would be mined just to produce a few grams of Radium, which was used to make glow-in-the-dark paints. So much waste rock was mined that it made ceramic glazes (one of the only other known uses) incredibly cheap and abundant.

You may have heard of it, it's called Uranium.

My understanding is that in this case DoorDash is keeping the extra, not the employee.