Expansion of the Universe Explained | Cosmology 101 Episode 1

Loving that last line. Thank you!

Thanks Katie I enjoyed episode 1. I took your book on holiday to Paphos, for some “light reading” …”the end of everything”…..what a great way for us primates to scratch our dense heads on whilst Chilling around the pool.

Really enjoyed this! One minor issue, though: the background music was a little too foreground, at least for me. I sometimes lost track of what was being said because the music was in the way.

That last point was a banger. I'm going to have to use sometime myself.

When i was a kid my dad tried to explain how knowing more meant there was more to know. He drew a circle and said everything you know is inside the circle and everything you don't is outside the circle. as you put more into the circle (learning) it expands, and when it expands it has a larger surface area and with a a larger area there is more to be learned. Hello from BlueSky

Best explanation ever. : )

Very good. Thank you, Katie. :-)

Love these videos!!

The background music is on-point.

Pretty cool segment.

'getting less dense' - very clever

I love this!! 🎉🤩✨✨✨

Perpetual, never ending creation... We are experiencing existence within our time frame.

Tom Murphy just released a similar video about the same time called "Metastatic Modernity #2: Cosmology" Are you two entangled?

I am ever so slightly less dense now, thanks!

Katie!!

That was a great explanation of expansion. You didn’t mention dark energy. Some people think that the expansion of the universe is accelerating. I don’t agree. There is a model in which the Milky Way galaxy is located 26 million light years from the centre of a finite universe with a space boundary. In this case the variation in the recession velocity is with distance not time. So the expansion of the universe is constant and the variation in the recession velocity of distant galaxies is due to movement through space caused by the gravitational effect of other galaxies. Richard

Making some sense of what this expansion means is something that's been bugging me (non-scientist) for a long time. I ran into very few popular science attempts to touch on the fundamental nature of spacetime in depth. Our universe's expansion is one of the few topics that's closely related. 12 years ago, a very interesting lecture was published on this channel (YT video name: "Fay Dowker Public Lecture - Spacetime Atoms and the Unity of Physics (Perimeter Public Lecture)" that I feel was a little better than most in touching on the subject. Basically we have two very distinct possibilities: A. Spacetime is fundamentally discreet (i.e. quantified) at an unimaginably small scale (e.g. Planck length). This would mean we can talk about spacetime atoms. The hard consequence is we're fundamentally blocked from knowing much at all about what's "in-between" these atoms as what happens there is outside our universe (or perhaps better said, it's outside the 3+1 dimensions we're aware of). In quantified spacetime there are extremely tricky questions to answer about what we now call fundamental particles. Are these particles always bound to just one spacetime atom or can they spread across more than one? Very likely they are spread across more than one which directly contests their fundamental nature. So in quantified spacetime, what we now call fundamental particles are most likely not fundamental. There are likely smaller things, which we may never even be able to probe individually, which are bound to one spacetime atom at a time. Another wonderful question immediately arises: Can fundamental particles travel and/or interact across spacetime atoms that are not apparently adjacent in our 3+1 dimensions? Very likely the answer is again yes, which again has massive consequences. It means the topology of our universe is necessarily one with multiple dimensions, some of which enable these "at a distance" interactions between atoms. Considering all of the above then in quantified spacetime we have the amazing possibility that "expansion" can (partially?/fully?) mean that new spacetime atoms pop into existence between existing atoms. How would nearby fundamental particles be influenced by that? That's a mind melter. One of the most difficult things to conceive of in quantified spacetime is a gravity wave. You may be tempted to think a gravity wave is just a waving of spacetime atoms but no, if it was 100% just that, the gravity wave would not be noticeable from within spacetime. Something else waves and one of the most fascinating possibilities is what waves is the rate at which time elapses. I wasted quite some time trying to imagine that. B. Or maybe spacetime is fundamentally continuous (this doesn't mean we don't have the means to probe below a certain length so we assume it's continuous, it means we determine that in our mathematical model of the universe spacetime MUST be continuous or else some other well tested fundamental aspects of our model unravel). Massive questions arise in this case too. Like, literally, what does it even mean to "expand" in this case? If you think about it in depth, expansion makes absolutely no sense here as we have nothing to compare it to. In macroscopic physics, all expansions are like those from (A) if you probe them close enough. Also, with (A) it makes sense to imagine the difference between particles (i.e. stuff that's already "in" our universe) and spacetime (the canvas on which particle live). But with (B) the difference between spacetime and particles becomes very blurry. Particles become more like a local property of spacetime. When the canvas is stretched the particles are stretched, that's a bit easier to ponder, but if you think about where the "new" canvas came from... seems a lot harder than with (A). It's also a lot more difficult to discuss about extra dimensions and non-local interactions with (B). Again it's equally difficult to imagine a gravity wave. Even though particles seem like local properties of spacetime in this case, a gravity wave is clearly distinct from particles and yet it affects them. I can't make sense of that at all. Fun stuff.

The universe density looks the same everywhere. It appears to be static. It's hard to believe that magical spacetime is expanding. Cosmological redshift looks similar to what we observe in the air. If we deposit sound waves into the air, the air will get hotter. The sound wave will speed up and redshift.

So that slinky is kind of terrifying. If the universe expanded in a big bang, could this be some kind of cycle? Where the universe will collapse at some point and have another big bang happen?