The present investigation [using Cepheid variables for the first time as an indicator of distances beyond the Magellanic clouds] identifies NGC 6822 as an isolated system of stars and nebulae of the same type as the Magellanic clouds, although somewhat smaller and much more distant. A consistent structure is thus reared on the foundation of the Cepheid criterion, in which the dimensions, luminosities, and densities, both of the system [NGC 6822] as a whole and its separate members, are of orders of magnitude which are thoroughly familiar. The distance is the only quantity of a new order. The principle of the uniformity of nature thus seems to rule undisturbed in this remote region of space.

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(Edwin P. Hubble, “NGC 6822, a remote stellar system,” Astrophys. J. 62 (1925), 409-433.)

Sean Carroll
The Biggest Ideas in the Universe
#22: Cosmology
https://youtu.be/tZQadPmTd84
1:59:14
(and there is a 90 minute Q&A follow up available.)

Steve–
It helps to think of all this as…..We are inside an expanding sphere of Space. The ‘big bang’ was not an explosion per se and can be best thought of as a moment in Time and not a physical location in Space.

Not really. The expansion of the universe means that everything is moving with the expansion and generally getting farther and farther away from us and everything else (even the ether and the dark matter, although the hypothesis is that the universe is expanding into a supply of dark energy, and the gain of all that energy provides the power to cause the observed increasing expansion rate).

The theory was developed because farther galaxies appeared to be receding away from us, the farther the faster, and it someone were to run in reverse a film of all this motion, then the film would show everything getting closer and closer until it all became one tiny blob of energy. The tiny blob would be the entire universe, which would be an inch in diameter, not many, many light years in diameter.

The generally accepted model of the universe is based upon the universe beginning as a tiny blob of enormous energy, suddenly expanding in a Big Bang, and all of space, time, mass, laws of physics, morals, ethics, and fattening foods were carried along with it as it expanded. Eventually, all that energy condensed into the matter that we see around us, and the microwave background radiation continues to exist Everywhere All at Once, if I may use a truncated movie title for effect.

Not only is each point in the universe the center of the uncentered universe, it is also where the universe began as a small ball.

Other models have been tried, including one in which the Earth was on the back of a large tortoise, which was resting on another tortoise, which was resting on another tortoise, which was tortoises all the way down. Feel free to choose your favorite model, because the Big Bang Theory is being questioned almost as much as the model with tortoises all the way down. I’m sticking with the Big Bang Theory, but only because I get to be the center of the universe and the source of the universe, which revolves (or expands) around me, and everyone is required to acknowledge that undeniable fact.

There being no center of the universe would explain why the background radiation is still detectable on Earth. Common sense says the radiation should be gone like a blast wave of an explosion that emanates from ground zero.

Without a universe center doesn’t that mean galaxy clusters are moving in random directions, independent of each other? But Edwin Hubble saw the distant galaxies moving away from us. Are there galaxy clusters moving in the opposite direction of our local group galaxy cluster, on a collision course with the local group?

I never knew the Lorentz transformations came from explaining Michelson Morley. I thought I remembered from collage the Lorentz transformation were derived from Relativity. I knew Einstein claimed not to know of Michelson Morley, and caltec covered that like a cliffhanger. I always suspected Einstein had to have known.

Correct. The current model (which could change due to JWST observations) is that there is no center to the universe, which means that every point is the center of the universe. The next time you say that someone thinks that he is the center of the universe, keep this in mind; although he may be egotistical, he is right.

“But the direction a galaxy is moving is not radially from the center of the universe since Andromeda and the Milky Way are moving on a collision course. Kind of confusing.”

As the universe expands (again, current model), the clusters of galaxies tend to move apart. The galaxies within each cluster can move independently or even collide, and they tend to form a center of mass that they don’t drift too far from. If one were drifting too far, then it could be moving at a velocity beyond the escape velocity for that cluster, and that galaxy could end up on its own in the universe.

Some clusters could also be drifting closer together, but the model and the observations tell us that the farther apart the clusters are, the more likely that they are drifting apart.

The universe is a strange and mysterious place. We understand things that we experience on our own scale, and we call this understanding “classical physics” or sometimes Newtonian physics. Atoms and the particles that made up atoms behave differently, and we call these behaviors particle physics and quantum mechanics. We observe strange things that are hard to explain on the scale of galaxies and the scale of the universe, and that is called astrophysics. Dark matter and Dark energy are two things that astrophysicists have deduced to explain a couple of the observed mysteries.

In the past year, the James Webb telescope has returned data that contradicts the model of the universe that astrophysicists made over the past century, confounding them. There will undoubtedly be a decade or more of argument and bickering until the field is able to once again come to a general agreement. This is yet another example of how science is never settled, that everything we know to be right and true is wrong; it is just that we don’t know it, yet.

There was a time, a century ago, when we thought that light waves propagated through the ether (also: aether), like waves on a lake. Ether was something that physicists deduced to explain the wave-like behavior of light. The concept of ether went away when quantum mechanics showed us how light waves can propagate without a medium, sort of like those waves on the lake but without the water. As I said, a strange and mysterious place.

Steve Richter: Present theory about the evolution of galaxies is that they grow as they absorb smaller galaxies around them.

And galaxies are not like the larger universe in that galaxies do not orbit around the center of the universe, correct?

But the direction a galaxy is moving is not radially from the center of the universe since Andromeda and the Milky Way are moving on a collision course. Kind of confusing.

Has Hubble seen any stars which are on their own, not orbiting a galaxy?