If bodies attract each other, then why is the universe expanding – quora gas tax in new jersey


This Ewok might well conclude that there must have been an event in the recent past that had caused all the bits to fly apart from one another very, very fast. And that while their mutual gravitational attraction was still working, it is not strong enough to have slowed the bits down very much.

If this Ewok knew some Newtonian physics, they could reason about the future too. They would separate two scenarios. If the initial velocity of the pieces were below some critical value, then eventually their mutual gravitation will bring the pieces back together into a future collision they could call the “Death Star big crunch”. Whereas if they started off above this velocity, then the mutual gravitation of the pieces will fall off faster than they were being decelerated by this same force, so the cloud-of-bits-of-Death-Star will continue to expand forever. [math]^1[/math]

Note that in both these possible scenarios, the Ewok would observe the pieces decelerating slightly as they expanded. In the first scenario the deceleration is large enough to reverse the velocities of the pieces and bring them back together. In the second scenario, the deceleration still exists, it’s just a bit smaller, and not enough to bring the pieces back together.

It’s all a bit different in General Relativity and when you consider the whole universe, but actually … not that different. So for much of the second half of the 20th Century, there was a question much like the Ewok’s question: are we below or above the critical rate of expansion? In one case, the expansion of the “pieces” would slow, stop, and then come back together in a big crunch, and in the other they’d still slow a bit, but ultimately continue expanding forever.

The universe is not expanding. The universe is not a chunk of latex rubber which can expand, stretch, bend, warp, distort, twist or anything remotely like that. The word “expansion” is just lazy language. What has been observed is that light from distant galaxies appears red shifted and if it is because of the Doppler effect and not just long distance travel through spacetime, it means galaxies are receding from us and from each other in some unknown geometrical manner because it is uniform in all directions and apparently centerless. Nothing has ever been observed to be expanding, so the balloon model is a failure because the dots representing galaxies expand along with the inflating membrane, and galaxies do not expand, nothing does.

Not only are galaxies apparently receding from each other (not all, but about 2 out of 3; one out of three are on collision courses so the model is even more complicated) but the further away they are, the redder the shift, implying accelerating expansion (inflation). That would be sensible in a static universe if long distance travel of light through spacetime caused frequency degradation (not that it can’t, but then we have to explain where does the lost kinetic energy go). The problem with the static universe model is that gravity would pull everything together and we do not observe contraction either, so “expansion” is preferred. But the word is misleading. It would be more accurate to say, uniform centerless galactic recession (UCGR) but that’s a clumsy phrase that doesn’t play well to a public already engaged in a furious debate about allocating more funds to a branch of science in which results are purely intellectual with no concrete benefit to society. So we are stuck with misleading phraseology like “expansion” and “space itself” (what the heck can that be), “time flows” even though everyone knows time is an abstract concept (like space) and not a fluid that can flow. I read an article recently about how scientists built a molecule sized heat exchange much like the heat exchange in an A/C compressor housing by transferring some heat from the cooler molecule to the warmer one. Since the usual motion of heat is from a warmer one to a cooler one, the headline breathlessly shouted, Physicists made “time run backward”. Yeah, and my central air conditioner is a time machine.

Time run backward; now let’s savor that peculiar abuse of language, as if time were a clock that runs forward or backward. Do you see the problem now? Words have a strange power over us to evoke images in our imagination and when they are used loosely, cause more confusion than the clarification that was intended by the use of words.