Evidence that the key assumption made in discovery of dark energy is in error • Hacker News Board

Re: Evidence that the key assumption made in discovery of dark energy is in error

#81

Post by mannykannot » Tue, Jan 07, 2020, 2:54 AM UTC

snowwrestler wrote: post #76

flashman wrote: post #34

To know if the universe is expanding, we need to know the following: how far away things are, and whether they're moving away from us. In an accelerating universe, there's evidence that things were moving away from us slower in the past. The evidence that things are moving away from us is that as the universe expands, the wavelength of any light travelling through it also expands, shifting it towards the red end of t…

If I am reading this correctly, in plain English what it seems like they are suggesting is that old Type Ia supernovae worked differently from newer supernovae; e.g. that a Type Ia supernova 5 billion years ago had a different brightness curve than a Type Ia supernova from 50 million years ago. On its face this seems like an extraordinary claim; I can’t think of how to square it with the (fundamental) assumption that…

Do the current models of dark energy not have it changing over time? Or at least allow for the possibility?

The idea that fundamentally, physical law does not change over time, is either a metaphysical or methodological assumption (or a bit of both), but it is certainly not an empirically-derived result, and it clearly does not rule out manifestations of those fundamental laws changing over time.

Re: Evidence that the key assumption made in discovery of dark energy is in error

#82

Post by 8bitsrule » Tue, Jan 07, 2020, 2:55 AM UTC

CoryG89 wrote: post #62

brylie wrote: post #53

Earlier quoted context omitted.

I'm not an astronomer, but "tired light" makes more intuitive sense to me to explain the redshift. In effect, we already know that matter can affect light through gravitational interaction. Since light is travelling so fast and far it seems intuitive thst interstellar matter, as fleeting as it is, could act to slow light down over these great spacetime distances.

This doesn't make much sense to me. The speed of light is a constant, right? Gravitational interactions may change the directional component, but the speed would remain constant, no?

The speed would remain constant; 'tired light' would shift to longer wavelengths (redden).

Fritz Zwicky proposed the idea in 1929 - didn't work out. In 1933 he 'inferred the existence' of dark matter/energy, after using the averaged speed of a group of galaxies to calculate their mass ... and found they were producing too little light to have that mass. And there it sits a century later. MON Dieu!

Re: Evidence that the key assumption made in discovery of dark energy is in error

#83

Post by ncmncm » Tue, Jan 07, 2020, 3:02 AM UTC

platz wrote: post #66

Sabine Hossenfelder comments on this paper: Dark Energy might not exist after all https://youtu.be/oqgKXQM8FpU

Amusingly, this video is about entirely different work that also calls into question the basis for claims about dark energy.

Nobody seems to be saying how the two results interact. Taking away dark energy twice could give us negative dark energy, which would be fun. I don't know whether unexpected negative dark energy would be more embarrassing than unexpected zero dark energy.

Re: Evidence that the key assumption made in discovery of dark energy is in error

#84

Post by yk » Tue, Jan 07, 2020, 3:02 AM UTC

crazygringo wrote: post #18

Do I understand correctly that this is actually saying that accelerating expansion of the universe may be in error? That there is, instead, no accelerating at all, but merely constant expansion? Or can there still be acceleration without dark energy? I'm unclear if they are essentially the same hypothesis or if there are more complicated subtleties I'm missing.

There is a standard cosmological model called LCDM model, Lambda Cold Dark Matter model, which is basically the minimal thing you can use to fit cosmological observations, it contains a cosmological constant and cold dark matter, that is dark matter that is heavy enough that it is cold in the present universe. From the cosmic microwave background and Baryon Acoustic Oscillations (BAO), that is basically the distribution of galaxies, you can measure values for your favorite cosmological model. There are additionally for the dark matter density galactic rotation curves and for the cosmological constant super nova data.

Now dark energy is basically another name for the cosmological constant. (In general relativity the cosmological constant gives you the curvature of empty space, and dark energy is the same term moved to the right hand side.) However, the philosophical difference is, that sufficiently funny particles, like for example the Higgs, can easily mimic the effect of an cosmological constant. So there is an industry of people who calculate the effects of different extensions of the standard model on LCDM cosmology.

Now, above I said that CMB, BAO and SN data all agree in cosmological observations on the value of the cosmological constant. So for it to be wrong, it needs to either evolve, or several different measurements need to conspire to mask the effect of an constant. So my assumption is, either their non standard evolution is compatible with LCDM cosmology, or there is something wrong with the analysis.

Re: Evidence that the key assumption made in discovery of dark energy is in error

#85

Post by ncmncm » Tue, Jan 07, 2020, 3:06 AM UTC

ltbarcly3 wrote: post #61

I guess people are going to act like I'm a lunatic, but of course it's wrong. Dark Energy violates basic conservation of energy, and the evidence for it has never been strong or convincing. Lots of us have been saying this since forever.

Conservation of energy has only ever been observed in local conditions. The universe is not obliged to respect our local expectations, and has always turned out to violate them in uncomfortable ways.

The ground looks flat near you (at least in Nebraska). The Sun seems to go around Earth.

Re: Evidence that the key assumption made in discovery of dark energy is in error

#86

Post by mannykannot » Tue, Jan 07, 2020, 3:09 AM UTC

ncmncm wrote: post #48

coliveira wrote: post #12

Earlier quoted context omitted.

> If these are both overturned it will be a huge blow to "scientists" credibility This is nonsense. Scientists have been wrong in several occasions, it is just part of the profession. For example, in the years leading to the discovery of relativity, many physicists believed there was something called "ether" that worked to fix the speed of light that they had evidence to be the same in all directions.

When chemists were asked, at the end of the 19th century, whether the the atoms in their molecular diagrams were real, they always said, "No, that's just a model we use." It wasn't until Brownian motion needed actual atoms that they began to say atoms had objective reality. Cosmologists could learn a lot from 19th-century chemists.

I think there were a lot of chemists at that time who were confident that atoms are real, but an influential group of philosophically-minded physicists (Mach, for one) objected to the claim on the basis that the evidence was circumstantial. They gave Boltzmann a good deal of unnecessary grief over the matter (no pun intended).

Re: Evidence that the key assumption made in discovery of dark energy is in error

#87

Post by galangalalgol » Tue, Jan 07, 2020, 3:22 AM UTC

pdonis wrote: post #38

unlinked_dll wrote: post #32

Earlier quoted context omitted.

it's my understanding that dark matter is another word for the indirect observation of matter that we can't otherwise detect, through gravity. I don't know if calling it a placeholder is the proper parlance. Dark energy is something predicted by general relativity and iirc it's what is behind the expansion of space (and acceleration of expansion).

> Dark energy is something predicted by general relativity Not really. GR can accommodate it just fine, but GR did not predict it. In fact, Einstein, who originally introduced the cosmological constant (which was the term then for what we now call "dark energy") in order to allow a static solution to his equation, thereby missed the chance to predict that the universe was expanding, a decade before Hubble's observati…

How much would the fate of the universe page on Wikipedia change with linear expansion? Do we have a bit longer before the stretch?

Re: Evidence that the key assumption made in discovery of dark energy is in error

#88

Post by igravious » Tue, Jan 07, 2020, 3:26 AM UTC

bananabreakfast wrote: post #77

flashman wrote: post #34

To know if the universe is expanding, we need to know the following: how far away things are, and whether they're moving away from us. In an accelerating universe, there's evidence that things were moving away from us slower in the past. The evidence that things are moving away from us is that as the universe expands, the wavelength of any light travelling through it also expands, shifting it towards the red end of t…

Speaking from the pov as a former astrophysicist, that definition of redshift is not quite accurate. While we have observed the universe expanding since Edwin Hubble published his findings 90 years ago, it was in fact the Friedmann equations produced 10 years earlier that established how it would work within the context of general relativity. The Universe is expanding at every known point at the same time at the same…

One thing I've never understood is this.

How do we tell the difference between the expansion of space and the dilation of time?

Given that space and time are crudely specking intertwined (spacetime) how do we know that the effect we see -- redshifting -- is due to the spatial expansion at every known "point" and not the temporal expansion (contraction?) at every known moment? Could not the spatial size of the universe be constant and its "clock" be being distorted?

Re: Evidence that the key assumption made in discovery of dark energy is in error

#89

Post by ncmncm » Tue, Jan 07, 2020, 3:26 AM UTC

mannykannot wrote: post #86

ncmncm wrote: post #48

Earlier quoted context omitted.

When chemists were asked, at the end of the 19th century, whether the the atoms in their molecular diagrams were real, they always said, "No, that's just a model we use." It wasn't until Brownian motion needed actual atoms that they began to say atoms had objective reality. Cosmologists could learn a lot from 19th-century chemists.

I think there were a lot of chemists at that time who were confident that atoms are real, but an influential group of philosophically-minded physicists (Mach, for one) objected to the claim on the basis that the evidence was circumstantial. They gave Boltzmann a good deal of unnecessary grief over the matter (no pun intended).

Yes, all chemists suspected atoms were real, but they were mostly careful not to claim to have evidence for it that they did not, in fact, have -- yet! Nobody but nobody was surprised when we turned out to really have atoms. It was all a relief, but it didn't change much about how chemistry was conducted. It made catalysis easier to understand, and ultimately DNA as a physical basis for life that made biologists generally very uneasy. Many had thought of themselves as studying something divine, and had to get used to being chemists.

Re: Evidence that the key assumption made in discovery of dark energy is in error

#90

Post by dieppe » Tue, Jan 07, 2020, 3:33 AM UTC

bananabreakfast wrote: post #77

flashman wrote: post #34

To know if the universe is expanding, we need to know the following: how far away things are, and whether they're moving away from us. In an accelerating universe, there's evidence that things were moving away from us slower in the past. The evidence that things are moving away from us is that as the universe expands, the wavelength of any light travelling through it also expands, shifting it towards the red end of t…

Speaking from the pov as a former astrophysicist, that definition of redshift is not quite accurate. While we have observed the universe expanding since Edwin Hubble published his findings 90 years ago, it was in fact the Friedmann equations produced 10 years earlier that established how it would work within the context of general relativity. The Universe is expanding at every known point at the same time at the same…

> The Universe is expanding at > every known point at the same > time at the same rate

This part I don't get (I am in no way versed in astrophysics).

If I am in a box, and that the box grows 10%, but that at the same time I grow 10%, what has changed?

I mean, if every point in the universe expands at the same rate at the same time, what does it change? Relatively speaking, everything is the same size before and after expanding right?

It feels a bit like expanding a 1 meter line and expanding the meter standard the same rate as the line.

If anyone has an explanation and is willing to spend some time writing it down, I would be most grateful :)

This itches my brain ^^