# How can one be sure that type-Ia supernovae have constant properties in time?

This type Ia category of supernovae produces consistent peak luminosity because of the uniform mass of white dwarfs that explode via the accretion mechanism. The stability of this value allows these explosions to be used as standard candles to measure the distance to their host galaxies because the visual magnitude of the supernovae depends primarily on the distance.

Could it be, however, that this (hypothesized) stability of the peak luminosity value is not constant in time? Let's assume the laws of physics didn't change since the big bang (this seems pretty obvious, but some physicists say these laws vary from place to place and from time to time).
This would imply that these "standard candles" can't be used for measuring the expansion rate of the Universe in the past? This, on its turn, could mean that dark energy may not exist after all (contrary to dark matter, the effects of which are certain, contrary to its Nature).

• My guts feeling tell me something to do with Chandrasekhar mass limit Jan 31, 2020 at 12:59
• @user6760 That's indeed a constant in time. Given that the laws of physics don't change in time, which seems pretty obvious to me. But maybe the white dwarfs in earlier times were composed out of different material as they are later on. Jan 31, 2020 at 14:09
• you of course assume that physics does not change with time, otherwise you can make any predictions you want
– user65081
Jan 31, 2020 at 22:12
• and candles have a range of values, when you far two far away and supernovas are less trustworthy, you can use other methods, see here en.wikipedia.org/wiki/Cosmic_distance_ladder
– user65081
Jan 31, 2020 at 22:15
• @Wolphramjonny If you know how they change in time you can make them. Feb 2, 2020 at 23:00

• @descheleschilder Anysotropies in CMB give a value of the curvature of the universe and parameters of cosmological models: $\Omega_0$,$\Omega_{dm,0}$,$\Omega_{b,0}$,$\Omega_{\Lambda,0}$ (curvature, darkmatter, barionic and dark energy). Feb 3, 2020 at 9:57