Isn’t this idea included or a product of the Big Bang Theory?
The second part of the question is, how come there are new galaxies being discovered if the universe is expanding faster than the speed of light?
Does light travel an infinite amount of distance? Isn’t luminosity or intensity of light a thing?
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>is it an accepted truth the universe is expanding?
Yes. We can measure it from the red-shift of other galaxies. The faster things move to or away from us, the wavelengths of light they emit get compressed or stretched.
>Isn’t this idea included or a product of the Big Bang Theory?
Tied to the hip with it. The “bang” in the big bang really wasn’t an explosion of stuff. It was more like “and explosion of space”. Space had to expand REALLY fast before the first second. And then of course, expansion slowed down from that rate. The question for a long time was “is it still expanding? Is it reversing? Is it going to reach a point of stability?” And the best answer we have so far, unless models change with new info, is that the rate of expansion is ACCELERATING. So maybe it’s just comes in jutters, for whatever reason.
>The second part of the question is, how come there are new galaxies being discovered if the universe is expanding faster than the speed of light?
Because plenty of galaxies are close enough that their light still reaches us. I could discover a new bistro down the lane if I hadn’t previously seen it. That’s not that far away and while the universe is expanding, it’s not going to escape my cone of causality any time soon. Likewise, a lot of galaxies are relatively “next door”. If you take a powerful telescope and point it at pretty much any section of inky black in the sky, and collect enough photons for long enough, you’ll find so many galaxies that they just look like stars. Which is what the [Hubble did](https://en.wikipedia.org/wiki/Hubble_Deep_Field).
>the universe is expanding faster than the speed of light?
Yeah, let’s hit that part again. There’s two concepts here: 1) The universe is most likely infinite. It just goes on forever. So no matter how small the rate of space expansion is, being cumulative, there will be a point X distance away that is expanding away from us at light-speed. Infinity plays weird games with a lot of math. 2) The VISIBLE universe is a known finite number. It’s the speed of light times the age of the universe in all directions. (~~minus a little~~ plus quite a lot (I got it backwards initially) since the playing field itself was expanding during that time). Every year, it’s diameter grows by 2 lightyears. It has a real and definite edge, but it’s OUR visible universe. Alpha Centari has it’s own visible universe, but shifted over that way a few light-years.
Since the visible universe grows every year, the rate of expansion at the EDGE increases. Even if the expansion wasn’t accelerating, we’d eventually hit a point where the expansion of space overcomes new space entering our visibility. But with the historic and current rate of expansion, and the age of the universe, we’ve already hit that point. Every year the edge of visible space is a lightyear farther away, but the stuff there is falling outside of our view. We’ll never interact with it.
>Does light travel an infinite amount of distance?
Yes. And infinitely fast, since it’s massless. That’s “at the speed of light”. It experiences no time in transit.
>Isn’t luminosity or intensity of light a thing?
For sure. Stuff at the edge of visible space is getting dimmer and dimmer. We’re making some really kick-ass and sensitive telescopes though.
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