[nabakin]

> type Ia supernovae, long regarded as the universe’s "standard candles", are in fact strongly affected by the age of their progenitor stars.

A key point in the article. From what I understand, this is the main way we measure things of vast distance and, from that, determine the universe's rate of expansion. If our understanding of these supernovae is wrong, as this paper claims, that would be a massive scientific breakthrough.

I'm really interested in the counterargument to this.

[negativelambda]

It could be a big discovery and it also aligns with the findings from DESI BAO [1] and by another Korean group using galaxy clustering to infer the expansion history [2].

[1] https://arxiv.org/abs/2404.03002

[2] https://arxiv.org/abs/2305.00206

[gorbot]

I'm dumb and barely understand things at a high level, but standard candles never sat right with me so it's interesting to hear that they might not be, but then again who knows.

[jiggawatts]

The idea is that standard candles are based on chemistry and microscopic physics only, not cosmology.

[alfiedotwtf]

If I remember correctly (sorry it’s been a while), the size of the star determines its colour, and the data suggests that the colour of stars fits nicely into the mass of a star (ie you’ll never see a star of X color thats Y kg)

[jiggawatts]

The rule is violated in all sorts of fun and interesting ways. There's white dwarfs, for one, then stars with varying levels of metallicity. Stars can merge, which does strange things to their position on the Hertzsprung–Russell diagram. There's oddball combinations like a red giant with a neutron star that has sunk into its core, called a Thorne–Żytkow Object!

Not to mention variable stars, novae, occultation by dust clouds, etc.

[alfiedotwtf]

Great Scott look at your username!

[basch]

This is mostly my physics ignorance talking, but if we measure distance in space-time and not just space, and speed or velocity is space-time/time (which somehow are both relative to each other) and the derivative of velocity is acceleration, cant acceleration mean either expanding "faster" in the sense of distance OR time speeding up or slowing down? All of it seems so self referential its hard to wrap around.

[cvoss]

We measure distance in space, and time intervals in time, and so velocity is just plain old distance/time. Special relativity doesn't change that. What changes is that if you start traveling at a different velocity, your measurements of distances and time intervals deviate.

The expansion rate of the universe is not a velocity in the usual sense of distance/time. It's actually in units of velocity/distance, which reduces to 1/time. An expansion rate of r Hertz means that a given span of distance intrinsically doubles every 1/r seconds. The objects occupying the space don't "move" in any real sense due to expansion. They just wind up farther apart because space itself grew.

And, just like measurements of distance and time, measurements of the expansion rate change if you change your velocity. There is a special velocity in our universe which causes the expansion in all directions to be the same. From this special perspective, which is traveling at a kind of cosmic "rest" velocity, you can calculate the expansion rate. It turns out that the Sun is traveling at approximately 370 km/s with respect to that special "rest" velocity.

[uecker]

Yes, it is the same thing, but since the objects are in free fall and there is no traditional force to cause the acceleration the better view point is that this is accelerated expansion of the universe. In a flat spacetime a forward light-cone can be identified with an expanding (no acceleration) universe where objects just fly away from a single point with constant but different speeds, i.e. an explosion. But in this model space as slice with the same local time after explosion is not flat. Also data seems to indicate that space is flat while space-time is curved on a large scale, so this picture is too simple.

[stronglikedan]

> If our understanding of these supernovae is wrong, as this paper claims, that would be a massive scientific breakthrough.

Indeed. It's so hard to definitively prove things that are, that the most significant breakthroughs prove things that aren't (so to speak), imho.

[JumpCrisscross]

> It's so hard to definitively prove things that are, that the most significant breakthroughs prove things that aren't (so to speak), imho

Significant breakthroughs do both. Prove things aren’t as we thought. And are as the new model suggests.