watchwolf is on a roll today. He spotted this error about 10 posts before I even made it.
That’s not even wrong … I swear that had nothing to do with my comment … my cat walked across my keyboard … it was hackers messing with my account … this still has to be my fault somehow …
Don’t make me explain why the speed of light is slowing down …
dE/dt= c[sup]2[/sup]∂m/∂t + 2m∂c/∂t
Which means that there is enough to produce a stellar/galactic wind… the particles of matter , dust, gets driven out. Mechanic energy …
Next thing is, the dust is in orbit and falling in and all its potential energy gets converted first into mechanical energy, and then through collisions, heat in the form of vibrations of atoms…
I guess this is the whole paradox, dark matter, dark energy thing. Measuring the rates these things happen at each point in the universe…
Not even wrong.
From what I can tell, the observable universe is some 260 Ym across, which means, if it is ~13By/o, there would be a nominally homogenous flux of photons and neutrinos plodding steadily outward, for an overall breadth of 500+ Ym There should be a wavefront that is a hint of what follows.
But, in those reaches, the distances between any two particles would start to exceed the average distances between galaxies, back here. Far space would be unimaginably rarified.
But that assumes that the outer universe is flat and simply-connected. In the absence of matter, there is no guessing what kinds of mischief spacetime might get up to. We have only really observed how stressed spacetime shapes up. Weird shit could be going on way out there.
I don’t understand why you are assuming there’s no matter beyond the observable universe. The universe could be anywhere from several to billions of times larger than the observable universe (or possibly even be infinite) and my understanding is that all of it has the same density of matter we see here.
dtilque covert the issue with just the “visible” universe, but I do want to point out that under the most common generally accepted current theories the matter isn’t flinging out, space itself is expanding.
While a flawed analogy, gravity is the weak force but is strong enough to prevent most of this expansion. It is not the galaxies and clusters that are expanding it is the room between them. If that expansion is happening at an accelerating rate like most modern theory suggest there will be a point in the future where expansion will exceed the speed of light and the entire non-local star-field will go dark.
As those photons travel through expanding space they are red-shifted, as the medium they are traveling through grows longer and at some point before expansion exceeds the speed of light they will be so low energy as to be undetectable.
More like there’s no good reason to believe it isn’t pretty much just like the observable universe. It could be billions of light years of lemon meringue pie. But it probably isn’t, because as far as we know there’s nothing special about our part of the universe.
Do photons ever…die? Or just wink out of existence? Is the ability of photonic energy to travel through space and time unlimited?
Is this statement really true? I mean, new stars are being born all the time and old stars are dying. Is there an inherent 1:1 balance in that?
Photons don’t experience time, their emission and absorption is a single event from their frame of reference, no matter how far or long they travel in our frame of reference.
Time is a phenomena reserved for those of us with mass and traveling slower than the speed of causality.
Except that photons are not always traveling at C. They slow through various mediums.
While that is the simple intuitive model, but not really descriptive of the effect. I am going to fail at providing an analogy as this is best described in mathematics, but the individual photon is not slowed, just the resulting detectable EM radiation.
First, there have been some recent tests in free space that also “slow” the light, but they do so by increasing the distance that the photon has to travel.
https://arxiv.org/pdf/1411.3987.pdf
I am mentioning this just to avoid non-related posts, but in the context of an individual photon in that case, which is not slowing it due in a medium like your post, the speed is not reduced, the path required to reach another location is lengthened.
As for slowing going through a media like glass, water etc.
In this case light is no longer just the disturbance of the electromagnetic field, but is also interacting with electrons within that substance. This results in a change in the phase velocity
In this case it is best to think of light as a wave and not a particle.
Imagine if you had two ponds a shared wall, not replace that shared wall with something similar to jello. A wave in one pond would vibrate the jello and transmit that wave to the other pond.
If the wave front in that jello was slower than in pure water the wave wouldn’t exit the other side as quickly as it was traveling in the pond.
When light goes through something like a lens, it goes through all of that lens at once, and those electrons that are interacting do not necessarily change in relation to each other at C.
But if we switch back to light as a individual particle, it has to travel at C, as it is mass-less, and all mass-less particles have to travel at C. But their combined wavefront doesn’t have to. This interaction is maybe best demonstrated through the effects of the “Airy disk”
Note this “slowing” is somewhat different than what happens in the middle of the sun where a photon can take up to 4000 years to reach the surface. And this concept also gets confused with absorption and readmission, but if you are interested in that subject here is a link:
In the case of this thread it is important to not confuse the propagation of an optical pulse, or an increase in path length with a change in the speed of causality or a slower than c photon.
Don’t confuse infinite vs finite with a simple quantity.
The number of stars could be ever-increasing from the Big Bang until now and into the future. But that doesn’t make Exapno’s statement wrong, either today or in the far future.
There’s no inherent reason the number of stars is fixed. Obviously we started with zero at the Big Bang and now there’s all the ones we do see and a whole bunch more we can’t see with current tech tools. So that proves the number’s not conserved up through the current epoch.
Simplifying mightily: As each star goes through its lifecycle it’s using up “fuel” and generating “exhaust” of other elements. There are various sorts of stars that can consume earlier stars’ exhaust as (at least part of) their own fuel. But this only goes so far.
Eventually the universe will start running low on star fuel. Then the number of stars, or at least living actively burning stars, will shrink. The universe will have lots of dead husks of stars.
Isn’t this dependent upon whether or not the Universe is infinite or finite itself?
Good point. I was implicitly talking about the known-to-be-finite *observable *Universe.
As to the (possibly nonexistent) rest of it, … well that’s an open question. As introduced here: Shape of the universe - Wikipedia
No it isn’t. If the Universe is infinite, then it has an infinite number of stars to go along with the infinite amount of hydrogen gas (star fuel). (I’m ignoring the possibility of space elsewhere being filled with lemon meringue filling. So sue me.) If you can see that locally, all the galaxies are running low on gas, you can be pretty certain they are throughout the Universe. And that doesn’t change if the Universe is infinite or finite.
The reason for this is that the entire Universe is the same age and has been going through the same aging process. There’s no region that’s younger or older than the rest.
But wouldn’t older galaxies run out of hydrogen first? I mean, not that it would really matter in the end to us here on Earth, but observationally speaking, couldn’t we quantify that?
It’s hard to imagine that at some point in time the Milky Way would run out of stars as they all die off.
That comes from belonging to a species that lives only the very tiniest sliver of a moment. In an open universe, the era when stars exist is just a brief moment at the very beginning.
Right, but what happens then? Life exists and evolves on newer galaxies far, far away?
Are you assuming that there must always be life somewhere?