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In this Wikipedia article there can be much read about type-Ia supernovae. One can read:

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).

See also this question and this one.

Deschele Schilder
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There is some research about star metallicity which points out that we can't use Supernovae Ia as standard candles: they don't necessarily explode always the same way. You can check out some of these works in Arxiv, for example: Impact of Metallicity in Ia or Measuring Metallicity of Ia Progenitors

Anyway, whether this is true or not, the dark energy is not only backed up in Supernovae Ia. Microwave background radiation measurements, gravitational lensing, primitive nucleosynthesis of light elements and the large-scale structure of the universe confirm also the existence of dark energy.

Wookie
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Isaac Domínguez Larrañaga
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