Is it at all possible that instead of being pushed away, we are instead getting pulled toward something huuuuuge via gravity? As if we are falling into something way greater than ourselves? I thought this was a wild idea but after I Googled it I found out that there is such a thing as a “Great Attractor”. Something 150 million light-years away is literally pulling all nearby galaxies towards it but no one knows exactly what it is.
So how do we know there aren’t any other Great Attractors, Greater Attractors, ad infinitum?
Everything not gravitationally bound is moving away from everything else. Every single point in space is growing larger. That means that things farther away from you are moving away from you faster then things closer to you. That’s true no matter where in the universe you are.
There’s not really an “away” from the big bang. That’s something science communicators fail to explain - the big bang happened everywhere. Space may have been infinite in size (we don’t know) and it still happened everywhere.
I’d recommend looking up the YouTube channel for FermiLab. They’ve got some excellent videos on the subject.
Also everyone always forgets to mention the “not gravitationally bound” part, so kudos for that.
So I’m getting bigger? How much per year?
No. Local attractive forces, like gravity, especially those at the atomic level, overpower the expansion for tightly coupled systems. So the earth isn’t expanding, and neither are the people on it. I don’t recall exactly what scale it kicks in at, but there is a good chance it’s not even affecting the distance between planets in a system. Most likely it only plays a role in inter-planetary-systems and larger. Ie, stars get further apart from each other.
Edit. This explains it better https://www.astronomy.com/science/does-the-space-inside-an-atom-expand-with-the-universe/
That says that the expansion really only applies to the space between galaxies. In anything smaller than that, gravity still overpowers the expensive forces. Making it far weaker than I initially thought.
It’s at a much, much larger scale** than that — our local group is collapsing in on itself, and it’s ~10M lightyears in diameter.
** talking about length scales only makes sense in reference to the specifics — two bananas separated by 10M lightyears, with no other matter nearby, would (I’m guessing) be expanded away, but a cluster of galaxies will not.
Using a banana for scale really made this so much better. :)
Yeah, finally I can imagine the vastness of space. Thank you, bananas!
Wouldn’t it cause some sort of force locally at the atomic level all the same even for tightly coupled systems? They shouldn’t feel the expansion as it is not a force from my understanding but just growth of space itself. But for example wouldn’t the orbit around an atom be off just so slightly that it would need to expend some level of energy to correct for lack of better word.
Or do we think this does happen but the amount is so small that we can not measure it experimentally in any way.
My understanding is that it does exert a force everywhere, even locally. It’s just so incredibly weak that other local forces dominate and overpower it. Take the classic example of expansion as ants on a balloon as it’s inflated. The expansion wants to pull them apart, but if they were tied to each other by thread, the thread would be stronger and they would stay together. The thread represents the inter molecular forces. Also remember that the expansion force is in every direction, without an origin, so from an atom’s perspective the force seems to push outward,not from the side, so there would be no “offset”.
Check your waistline to find out.
The forces that hold your body together are many, many orders of magnitude stronger than the acceleration due to the expansion of space.
Thank you so much for the explanation!
I’m going to sound like a total idiot but if our universe was at the center of a ginormous sphere could that give an illusion that every point in space was moving away from another when in fact we could all be falling (getting pulled by gravity) toward whatever edge of the sphere we are closest to?
Kind of a tangent at this point, but there is a very good reason that that couldn’t be the case: according to the shell theorem , nowhere in the interior of a spherical shell of matter experiences any net gravitational force – wherever you are inside the sphere, the forces counteract exactly.
Otherwise, though, the metric expansion of space is different from typical movement, and it isn’t correct to say that things or being pushed or pulled. Rather, the distance between every pair of points in the universe increases over time, with that rate of increase proportional to the points’ distance. Importantly, for very distant points, the distance can increse faster than the speed of light, which would be disallowed by any model which describes the expansion in terms of objects moving in a traditional sense.
Not unless we were directly in the center of it, in which case everything would seem to move away from us. But even then, if I’m not mistaken, physicists and astronomers have also proven that other objects are also moving away from one another too.
We can tell how something is moving based on the shift of its light, like the Doppler effect. The further something is the more its light is shifted, which was how we came to know this phenomenon in general of increasing size of space between all things.
What if everything is just getting smaller and smaller, so it just appears that everything is getting further away from everything else? Eventually, everything will be really tiny, but we won’t notice, because everything else will be the same smol also.
Lol if joking. If not, I’m sorry but you severely misunderstood what is happening here
Totally just joking. But I like to play with ideas, even absurd ones. So partly not joking also?
The Universe probably wouldn’t fit in a sphere of any size and it very well may be infinite.
But looking at a very large spherical region like the visible universe from our perspective here on Earth, everything is moving away from us. If objects were being pulled towards one particular edge of our imaginary sphere, it would look very different. We’d see a clear drift in that direction, but it all looks pretty even across every direction we look.
You are right that things would still look like we’re accelerating away from us, even if we were actually contracting.
Interesting hypothesis! How do we investigate?
What could we expect from a large central gravitational point? We should have other signs of the gravity well:
We would expect a point that we contract towards (and that seems ill fitting, as we see the expansion moves as the observer (including earth) moves), we would expect some kind of mass or similar effect, which would also have a size to fit it in (we know that gravity works different when you’re inside the mass, and we would be able to see it, much like black holes or dark matter), we would expect things to orbit the gravity well (which we know that at least our galaxy doesn’t orbit us).
You might want to actually check on these things to make sure they apply and are true, but at least at first glance it seems the expansion is better explained without a central gravity.