2 ms·

I'm not an expert, but I think it's like this: If the universe were expanding uniformly, we would see galaxies moving away from us. The further away they are,

I'm not an expert, but I think it's like this: If the universe were expanding uniformly, we would see galaxies moving away from us. The further away they are, the faster they would move. Distance and velocity would have a linear relationship, with the Hubble Constant as the scaling factor. But what we actually see is that, if we measure precisely enough, galaxies further away are moving faster than that. The conclusion is that the expansion is accelerating.

pdonis 3y ago
> galaxies further away are moving faster than that No, you have it backwards. Accelerating expansion means, roughly speaking, that we see galaxies further away moving away slower than a "uniform" expansion would predict. Remember that we are seeing galaxies further away as they were a longer period of time ago--so "accelerating expansion" means the universe was expanding slower then, when the light was emitted, than it is now. Actually, though, we don't observe the distance to a galaxy directly. We infer it from other observations. The actual observed quantities are redshift, brightness, and angular size, and the relationship between those three observed quantities is what tells us the expansion history of the universe.