Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

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

phys.org

Post reply on HN
Print view View original

71–80 of 295 posts

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

#71

Post by ncmncm »

phkahler wrote: post #50
empath75 wrote: post #22

Earlier quoted context omitted.

Scientist have no idea what dark matter or dark energy is so it’s not like our world would be overturned. If it turns out to be wrong assumptions, that’s fine. Although it would be embarrassing.

The problem is that these topics get enough press that the general public has heard of them. It's nice that there are no obvious consequences if dark matter or dark energy turn out to be fiction. But the public will hear that "scientists" were wrong about these things they've been talking about for 50 years. Then the public will get another report on a topic like climate change which is also proven by "scientists" al…

Our only recourse will be, "Well, you know, cosmologists. They don't behave like real scientists." That will sound suspiciously like "no true Scotsman", but there really is a difference between science with and without consequences.

People were forced to take particle physics seriously, and cosmology slipped in on its coattails.

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

#72

Post by ncmncm »

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?

It was expressed clumsily. The idea would be that photons can lose energy over time or space. One problem is that they would all have to lose energy at exactly the same rate as neighboring photons, so be a property of the space they are going through, not the photons themselves.

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

#73

Post by doodliego »

carbocation wrote: post #8
jshevek wrote: post #2

"...Prof. Young-Wook Lee (Yonsei Univ., Seoul), who led the project said, "Quoting Carl Sagan, extraordinary claims require extraordinary evidence, but I am not sure we have such extraordinary evidence for dark energy. Our result illustrates that dark energy from SN cosmology, which led to the 2011 Nobel Prize in Physics, might be an artifact of a fragile and false assumption."" Is he implying that other cosmologists…

This doesn't really address your point, but the 2011 physics Nobel [1] said that "What is known is that dark energy constitutes about three quarters of the Universe." Not saying the Nobel write-ups constitute evidence, but dark energy has certainly been popular, at least. 1 = https://www.nobelprize.org/prizes/physics/2011/press-release...

The Luminiferous Aether was popular too.

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

#74

Post by njarboe »

MiroF wrote: post #60
awb wrote: post #27

Earlier quoted context omitted.

> Is he implying that other cosmologists have proceeded as if dark energy is well evidenced? I thought dark matter and dark energy are simply placeholders for a discrepancy we see between our models of the universe and our observations. No?

No - this article aside, most of the evidence suggests that this is matter that is actually there, not just an error term that we have added to our models.

This article is about dark energy, not dark matter. IANAC, but I think the evidence for the existence of dark matter is stronger than dark energy.

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

#75

Post by rs23296008n1 »

Good. Science is meant to be a honest search for facts: data, knowledge and wisdom. Being wrong is a feature. "I don't know" is an acceptable starting point with no shame attached. Being certain means a mountain of data to back it up. Being allowed to be wrong is a requirement. Anyone saying a scientist can't ever be wrong is likely placing oddball limits on progress that will only damage and limit the future[1]. How can you experiment if you can never be wrong?

It would be good if people knew about the mountain-of-data aspect of science. Even with that mountain, subtleties creep in and plenty of surprises still remain.

Even something like water probably has properties we are clueless about. Interesting aspects that might redefine science itself and create entirely new approaches to medicine or manufacture or whatever. Maybe if you change temperature and pressure enough in the right way you end up with exotic metallic / bonding properties. Or some new water-based ion structure having other properties. Who knows? Maybe not. Perhaps water is what it is and there is not much more to learn. Asserting we already know everything about water leads to dogma[2] and inflexibility. That's just one example.

Dark matter/dark energy may be a rounding error for all I know. Good. Now we know about the error. We* likely asked a bunch of other questions as well and now we have new answers about to appear because now that error has been confirmed.

* not me.

[1] being wrong about bridge structure is unhelpful as you drive over it. That kind of wrong is related but I'm not directly addressing that.

[2] dogma has expectations, rules and consequences. Science has plenty of people who forget this and turn their understanding into dogma. That too is a experience generating moment that will catch up with them later. Mountain-of-data + knowledge + wisdom.

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

#76

Post by snowwrestler »

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 the laws of the universe have not changed during its lifetime.

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

#77

Post by bananabreakfast »

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 rate. However, this is only an observable effect over > 10 Mpc of distance (e.g. extra-galactic distances). This is far too large to effect a point particle like a photon no matter how far it travels so I'm afraid your analogy of a rubber sheet is incorrect.

The lengthening of said photon's wavelength comes instead from doppler expansion due to the nature of differing relativistic reference frames.

According to our local reference frame, doppler effects of nearby stars and galaxies are only due to local motion such as Andromeda being blue shifted as it approaches us for our eventual merger. However, as you go further and further out from our galaxy the metric expansion of spacetime begins to dominate the relative motion of all bodies, leading to observing progressively redder and redder light curves. A galaxy billions of light years away is perceived to be moving away from our reference frame at a significant percentage of the speed of light!

However, if you were to change our relativistic reference frame to match a distance galaxy's you would not see its photons "stretched out" but in fact they would look completely unshifted despite having traversed nearly all of spacetime, expanding as it went.

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

#78

Post by ncmncm »

wallace_f wrote: post #59
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.

It might be cultural. I think it is. Being unsure or humble is not valued as much as it should be.

It is valued more in more consequential fields. What cosmologists believe never has any legitimate effect on public policy, except to the degree that they command budgets for telescopes, accelerators, and detector arrays.

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

#79

Post by StanislavPetrov »

AnimalMuppet wrote: post #5
jshevek wrote: post #2

"...Prof. Young-Wook Lee (Yonsei Univ., Seoul), who led the project said, "Quoting Carl Sagan, extraordinary claims require extraordinary evidence, but I am not sure we have such extraordinary evidence for dark energy. Our result illustrates that dark energy from SN cosmology, which led to the 2011 Nobel Prize in Physics, might be an artifact of a fragile and false assumption."" Is he implying that other cosmologists…

It is my impression that dark energy is generally accepted in cosmology. Whether that counts as "proceeding as if dark energy is well evidenced" is perhaps a different question. If everyone believes it's there, but nobody knows what it is, well... there was still something that convinced them that it was there. That something should be evidence. Is it enough to count as "well evidenced"? Perhaps not, especially if th…

>If everyone believes it's there, but nobody knows what it is, well... there was still something that convinced them that it was there.

The article stipulates what convinced these people that it was there, namely that they rested their conclusions on an assumption that turned out to be wrong.

This result is based on the assumption that the corrected luminosity of SN Ia through the empirical standardization would not evolve with redshift.

Which is another good reason not to make conclusive judgements based on unproven assumptions (not that everyone that "dark energy" must exist, but many did, and some people still cling to it even if the face of this study). It is also a good example of why one should never give credence to a theory or a supposition based on how many other people give it credence - stick to what you can prove.

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

#80

Post by enkid »

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…

You're not reading this correctly. It's questioning the assumption that the Supernova are of the same brightness no matter the age of the star. Because the supernovaing stars are on average older now then they were in the early universe, there's a systemic bias in the data making it seem like there is red shift when there is not. No new physics required outside of a new understanding of how Type Ia supernova work.
Post reply on HN