The universe's expansion may actually have started to slow rather than accelerating at an ever-increasing rate as previously thought, a new study suggests.
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How do you tell the difference if all you can do is look at 1a supernovae redshift? Also, if velocity is dx/dt and the distance is changing, what is the difference?
How do you tell the difference if all you can do is look at 1a supernovae redshift?
If it was just standard motion, we’d expect to see a more-or-less random distribution of rates as we looked around: some things should be getting closer, some things should be moving away slowly, and some things should be just hanging out. That’s not what we see. Instead, no matter where we look, it appears that everything is receding from us at a rate that is proportional to distance–the further away something is, the faster it is receding. Since we assume that we aren’t in a privileged position in the universe (that is, we assume we’re not at the center of the universe), the best available explanation is that the actual distances are expanding. The further away something is, the more space there is between us and it, and so the faster it appears to recede. Since we’re not in a special position, that means every other observer anywhere in the universe should see the same thing.
If I’m sitting still and you’re sitting still and then an earthquake splits the earth and moves us further apart, you could say that you didn’t budge but I moved twice as fast away from you, because reference frames are weird like that.
The redshift is tied to velocity but distance can be measured with the “standard candle method” where a “standard candle” is a star/body that we know the size and distance of. I don’t remember/understand the specifics of how a standard candle comes be (telescopes I guess?) IIRC they use a bit of trigonometry along with the flicker rate/brightness to find the distance of bodies.
So they have a way to measure the distance completely independently of how they measure velocity (redshift/blueshift). Those values didn’t match up but the distance between bodies was observed to be constantly increasing across the board which is why they came to the expansion conclusion.
How do you tell the difference if all you can do is look at 1a supernovae redshift? Also, if velocity is dx/dt and the distance is changing, what is the difference?
If it was just standard motion, we’d expect to see a more-or-less random distribution of rates as we looked around: some things should be getting closer, some things should be moving away slowly, and some things should be just hanging out. That’s not what we see. Instead, no matter where we look, it appears that everything is receding from us at a rate that is proportional to distance–the further away something is, the faster it is receding. Since we assume that we aren’t in a privileged position in the universe (that is, we assume we’re not at the center of the universe), the best available explanation is that the actual distances are expanding. The further away something is, the more space there is between us and it, and so the faster it appears to recede. Since we’re not in a special position, that means every other observer anywhere in the universe should see the same thing.
Clever. That makes a lot of sense, thank you.
If I’m sitting still and you’re sitting still and then an earthquake splits the earth and moves us further apart, you could say that you didn’t budge but I moved twice as fast away from you, because reference frames are weird like that.
The redshift is tied to velocity but distance can be measured with the “standard candle method” where a “standard candle” is a star/body that we know the size and distance of. I don’t remember/understand the specifics of how a standard candle comes be (telescopes I guess?) IIRC they use a bit of trigonometry along with the flicker rate/brightness to find the distance of bodies.
So they have a way to measure the distance completely independently of how they measure velocity (redshift/blueshift). Those values didn’t match up but the distance between bodies was observed to be constantly increasing across the board which is why they came to the expansion conclusion.