Cepheid variable stars have periodically varying luminosity ( energy of photons released/s), where the period is a function of luminosity. We know observable brightness as a function of distance from a star and its luminosity. By checking if a star varies in brightness, recording its period and measuring its luminosity, we can estimate its distance from us.
This is in fact part of how we bootstrapped our map of the universe, by using cepheid variable stars as a sort of standard candle. It lets us figure out nearby galactic distances, and hence estimate the universe is >milllions of years old.
In fact, if I recall rightly, they’re what allowed to figure out how far away type 1a supernovae were and hence realise they have similair peak luminosities, and hence can be used to figure out distances.
This isn’t really simple though, is it?
Uh, what else. I guess looking at how far away the moon is from the earth + the fact that the earth and moon crashed into each other a long time + its velocity moving away from us could let us guess how long ago they crashed into one another? The maths is not hard, but the physical model is a bit complex.
I almost want to say something like “simple gravitational models of galaxy fomration imply the universe must be X millions of years old” but I don’t know much about galaxy formation, nor do I know how dark matter complicates things.
Oh, I guess the relative concentrations of uranium and its decay products in the earths crust could be used to estimate the age of the universe + the fact they form in supernovae.
Uh, the existence of large black holes implies a weak upperbound on the age of the universe, given black hole evaporation rates.
Cepheid variable stars have periodically varying luminosity ( energy of photons released/s), where the period is a function of luminosity. We know observable brightness as a function of distance from a star and its luminosity. By checking if a star varies in brightness, recording its period and measuring its luminosity, we can estimate its distance from us.
This is in fact part of how we bootstrapped our map of the universe, by using cepheid variable stars as a sort of standard candle. It lets us figure out nearby galactic distances, and hence estimate the universe is >milllions of years old.
In fact, if I recall rightly, they’re what allowed to figure out how far away type 1a supernovae were and hence realise they have similair peak luminosities, and hence can be used to figure out distances.
This isn’t really simple though, is it?
Uh, what else. I guess looking at how far away the moon is from the earth + the fact that the earth and moon crashed into each other a long time + its velocity moving away from us could let us guess how long ago they crashed into one another? The maths is not hard, but the physical model is a bit complex.
I almost want to say something like “simple gravitational models of galaxy fomration imply the universe must be X millions of years old” but I don’t know much about galaxy formation, nor do I know how dark matter complicates things.
Oh, I guess the relative concentrations of uranium and its decay products in the earths crust could be used to estimate the age of the universe + the fact they form in supernovae.
Uh, the existence of large black holes implies a weak upperbound on the age of the universe, given black hole evaporation rates.