Not claiming that you should have or would have. Just providing confirmation that you were attempting to teach me to suck eggs.
Eh. There are people in this thread who don’t know the subject so I was trying to be polite in case you were one, while recognizing that it might be a joke.
The raisin cake analogy is very old, of course, and was very old six years ago. It apparently dates back to Edwin Hubble himself, who used raisin pudding as the analogy.
That seemed a bit weird since I didn’t think of pudding as expanding in any way, but it seems he was using the British “general desert-ish item” meaning, not the American “sweet creamy goo” meaning.
He spent three years at Oxford as a Rhodes scholar. That must have had an impact.
This is the aspect of cosmological expansion which puzzles me most. Presumably the expansion doesn’t happen at a scale of the space between atoms in matter? The Earth itself, I’d guess, doesn’t expand in size because nuclear forces/gravity prevents this. But does the space between planets in a solar system increase? Between solar systems?
Gravity overcomes expansion on scales up to clusters of galaxies. Remember, the expansion is proportional to distance (this is what makes it possible for “every point to be the center”). On a scale as small as a solar system, the effect would be ludicrously small. For instance, the distance between the Earth and the Sun would be increasing at a rate of about 10 meters per year.
On the small scale (like your body or the earth) the forces between the atoms and molecules far overwhelm the forces of the expanding universe.
Which is to say you are not expanding (unless you count the Big Mac you had for dinner).
Even gravity can be enough and gravity is a very weak force (which is why we do not see galaxies being torn apart…dark matter may be involved but that is still a question mark).
Thanks; though this does rather contradict the idea of expansion happening at all scales, fractal-like, if it’s actually nullified by other forces, between anything smaller than galactic clusters.
But that would add up over time.
If the earth was moving away from the sun due to expansion of the universe at 10 meters/year it would be something like 40 million kilometers further away since the beginning of the solar system. About 25% more than it is now (ballpark).
Would that untether the earth from the solar system? (I really don’t know)
And it turns out the Earth is moving away from the Sun at a much smaller rate: 15 +/- 4 m/century, or 15 cm/year. Ref: Krasinsky and Brumberg:
No. That would still be closer than Mars’ current distance.
It’s not nullified, it’s just washed out.
The forces holding solid objects together are many, many orders of magnitude greater than the dark energy trying to force them apart. Even the gravity of the Sun on the Earth is many orders of magnitude greater. Within a galaxy, the force of gravity is still significantly stronger, and only when you get past the scale of galaxy clusters does the dark energy start winning out over gravity.
So, the expansion happens at all scales. Space is expanding within your atoms, between your atoms, in your cells, and even between your body and the chair. It just can’t overcome the forces holding those things together.
That assumes the earth’s orbital speed never changes. Would that speed change if the expansion of the universe was the cause of the distance change?
To be fair, there are still a lot of unknowns about dark matter, dark energy, the Big Bang, early inflation of the universe (why and how). That’s what makes JWST so exciting - it may finally give us a view into the early universe that helps us answer these questions.
Take that paper I mentioned before: Still very preliminary, but it seems to suggest that galaxies were already well formed very early in the period of re-ionization - an unexpected result. Another paper based on that first image shows that the decline in galaxy count in the early universe is not as steep as theory predicts.
There is still a whole lot wrong or incomplete in our understanding of cosmology, which is why we invested so much in JWST.
The orbital speed depends on the distance between the two objects: more distance implies lower speed. But the same effect would be working on Mars. And every other planet and planetoid. Their proportional rate would stay the same. Has stayed the same if you posit a 40 million km change over the solar system’s life.
Expansion is weird. When those very distant galaxies emitted the light that we now see, some of them were less than a hundred million light years away from here. But because of expansion, the light has now had to travel more than thirteen billion light years though space. During that time, the galaxies concerned have moved much further away, and are now about 46 billion light years away.
And yes, during that time, nearly all of the stars in those galaxies have been replaced by new ones (it is just possible that a few red dwarfs survive from those times).
(note- I haven’t got the exact figures for any of these distances - they are just a rough estimate by me. If anyone knows the real numbers I’d be very interested.)
Are you sure?
I mean, if the earth is being moved away by universe expansion where does the earth’s orbital speed go as it moves further away? We need to account for the energy in the system.
IANAPhysicist
Expansion doesn’t really apply to objects that are gravitationally bound. Galaxies aren’t growing in size due to expansion. In fact, one day the entire universe will be expanded out of our view - except for our local group of galaxies, which are gravitationally bound and will retain the same relationships, adjusting for regular motion.
Assuming that dark energy is a constant, and is not increasing over time. The scientific consensus tends to favor the former, but the latter is not ruled out.
If dark energy is increasing, it’ll rip apart the galaxy clusters, then the galaxies, then stellar systems, then stars and planets, then objects like people, and eventually even subatomic particles.
Yeah, that’s true.
I think the answer is that the expansion is adding energy to the system. It would be similar to a body coming in and perturbing an existing body into another orbit. You have to use both bodies to account for the resulting energy levels.