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

#211

Post by empath75 » Tue, Jan 07, 2020, 3:43 PM UTC

ncmncm wrote: post #71

phkahler wrote: post #50

Earlier quoted context omitted.

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.

Cosmologists are behaving like real scientists. There is a gap in our knowledge of physics which appears to be dark matter and dark energy. That's something that needs to be resolved, one way or the other. Currently they are expending a lot of effort looking for dark matter and energy. If it ends up being wasted effort, that would be embarrassing, but it wouldn't have been wrong to look.

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

#212

Post by 317070 » Tue, Jan 07, 2020, 3:52 PM UTC

dieppe wrote: post #90

bananabreakfast wrote: post #77

Earlier quoted context omitted.

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…

It boils down to this: You take a bowling ball, and put it 1 meter stick away from you at zero velocity compared to you. Assume that at this distance, no forces are exchanged between you and the ball. You wait a billion billion gazillion years, take your meter stick again and measure the distance between you and the ball, and notice it is now 2 meters away. It is the distance between you and the ball that has grown.

Note that the ball has not grown twice its size. The sizes of atoms and molecules have not changed (as they have mechanisms to keep them exactly the size they are, despite space growing). It is only when there are no mechanisms or forces to keep distances between objects fixed, they seem to drift apart very slowly. The question the article addresses, is whether that growth is accelerating or not.

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

#213

Post by hibbelig » Tue, Jan 07, 2020, 4:02 PM UTC

galaxyLogic wrote: post #166

Hendrikto wrote: post #97

Earlier quoted context omitted.

Your interpretation of the expansion is incorrect. Basically, it looks like all points are moving away from each other over large distances. It is easier to understand in 2D: Imagine a deflated balloon with two dots drawn on it. When you inflate the balloon, its 2D surface increases, which results in the two points "moving away" from each other, without either of them actually moving. It‘s just that the surface on wh…

> looks like all points are moving away from each other ... Do you mean all particles are moving away from each other? I think the question here was what would it mean for "points" to move? What are points anyway?

The analogy was dots on a balloon, and the next sentence used "points" instead of "dots" but meant the same analogy.

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

#214

Post by AnIdiotOnTheNet » Tue, Jan 07, 2020, 4:13 PM UTC

ncmncm wrote: post #29

Haha, called it! Feynman warned about this specific phenomenon: basing new physics on the points at the extreme end of your graph, where the measurements are least reliable. In this case, these points correspond to demolition of the most distant and youngest stars in the sample, which could differ in many ways from the common, much more recent events. Low metallicity is a difference that is obvious to every AP, but t…

> Haha, called it!

One or two years from now I invite you to take a look back at this comment and see if you still feel so smug. This is a relatively recent paper, give it some time to be chewed up and spit out by the cosmological community before hailing it as the deathknell of a decades old tricky problem.

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

#215

Post by Certhas » Tue, Jan 07, 2020, 4:32 PM UTC

shpeak wrote: post #183

Certhas wrote: post #169

Earlier quoted context omitted.

No space really is expanding. Think of it this way: You have a rubber band and you pull it apart, if you place two beads on the rubber band the distance between the beads will increase (even though they don't move relative to the rubber). But if you connect the two beads by a strong spring, then their distance will stay the same, despite space expanding. The force of the spring makes them move (relative to the rubber…

Such counteract action will make lot of side effects, which can be measured. For example, trajectories of separating or oscillating bodies will be slightly curved. Do you have any experimental support for this theory?

The effect of the expansion of the universe on bound systems is far to small to be observed. Two objects 1 meter apart would move at a speed of 10^-17 m/s. Utterly unobservable. But we know space is expanding by looking at things that are super far away from us and that are not bound.

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

#216

Post by Certhas » Tue, Jan 07, 2020, 4:33 PM UTC

shpeak wrote: post #189

DavidSJ wrote: post #185

Earlier quoted context omitted.

This isn’t Certhas’s personal theory. It’s part of standard cosmology, called the metric expansion of space . That term should get you pointed in the right direction if you want to learn more about the evidence for it.

It's too complex to explain, I will not understand it. Right?

It's not, but it might take more work than reading a few HN comments.

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

#217

Post by Koshkin » Tue, Jan 07, 2020, 4:43 PM UTC

roywiggins wrote: post #201

Koshkin wrote: post #186

Earlier quoted context omitted.

> relative to the rubber This makes me uneasy about your analogy. It’s like saying “relative to space” which is nonsense. Also, why would space limit itself to only expanding outside a physical body?

You can't make an electron bigger, so it can't be stretched out. Other point particles are the same. The forces that hold physical stuff together are much more powerful than the gentle expansion of space, so we don't see people and planets dissolving.

Indeed you can, if you realize that the place occupied by the "point particle" is described by its wavefunction.

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

#218

Post by Koshkin » Tue, Jan 07, 2020, 4:48 PM UTC

galaxyLogic wrote: post #166

Hendrikto wrote: post #97

Earlier quoted context omitted.

Your interpretation of the expansion is incorrect. Basically, it looks like all points are moving away from each other over large distances. It is easier to understand in 2D: Imagine a deflated balloon with two dots drawn on it. When you inflate the balloon, its 2D surface increases, which results in the two points "moving away" from each other, without either of them actually moving. It‘s just that the surface on wh…

> looks like all points are moving away from each other ... Do you mean all particles are moving away from each other? I think the question here was what would it mean for "points" to move? What are points anyway?

A point (in space) is something that could be occupied by an object.

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

#219

Post by roywiggins » Tue, Jan 07, 2020, 5:36 PM UTC

Koshkin wrote: post #217

roywiggins wrote: post #201

Earlier quoted context omitted.

You can't make an electron bigger, so it can't be stretched out. Other point particles are the same. The forces that hold physical stuff together are much more powerful than the gentle expansion of space, so we don't see people and planets dissolving.

Indeed you can, if you realize that the place occupied by the "point particle" is described by its wavefunction.

I know! But when you poke it, it still acts like a particle and the wavefunction localizes again, right? It doesn't exactly "puff up" like a billiard ball. Electrons don't really get bigger when they are put into states where their position is less localized.

But the expansion of space does "stretch" light- or at least, the wavelength gets longer, so it's not not happening.

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

#220

Post by bananabreakfast » Tue, Jan 07, 2020, 5:45 PM UTC

Koshkin wrote: post #186

Certhas wrote: post #169

Earlier quoted context omitted.

No space really is expanding. Think of it this way: You have a rubber band and you pull it apart, if you place two beads on the rubber band the distance between the beads will increase (even though they don't move relative to the rubber). But if you connect the two beads by a strong spring, then their distance will stay the same, despite space expanding. The force of the spring makes them move (relative to the rubber…

> relative to the rubber This makes me uneasy about your analogy. It’s like saying “relative to space” which is nonsense. Also, why would space limit itself to only expanding outside a physical body?

It does not. It expands at every point in spacetime. This effect is quite literally negligible on all length scales smaller than far extra-galactic distances.

It is equivalent to asking why a car driving towards me does not turn blue due to doppler shifting. Except even more negligible than that.