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A Physicist Who Denies That Dark Matter Exists

cosmos.nautil.us

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Re: A Physicist Who Denies That Dark Matter Exists

#141

Post by snowwrestler »

Paul-ish wrote: post #129
snowwrestler wrote: post #92

Earlier quoted context omitted.

> Evidence for atoms and protons was already there before they were "invented". Right, and there is also evidence for dark matter.

I think arenaninja is saying that the theoretical models predicted those things, then empirical experiments later confirmed them. (I don't know if this is actually the case) This gives the theories credibility as being predictive. In this case we have a theoretical mode, but we later notice our empirical data doesn't match this. Both MOND and dark matter are an attempt to patch up our existing theory to explain what…

It's not the case--protons were observed first, and then theory was developed to explain them, among other things.

General relativity might be wrong, but it's probably not over-fitted because it's quite simple as far as theoretical constructs go.

And it has a pretty good track record. Both black holes and gravity waves were "invented" because the theory seemed to indicate that they should exist, even though there was no evidence yet. Both were spectacularly confirmed last year.

That said, we know there is some shortcoming in either GR or quantum mechanics (or both), because they don't agree under certain conditions. Dark matter, being a gravitational phenomena that seems like it might be a new kind of particle, is potentially in that same area.

Re: A Physicist Who Denies That Dark Matter Exists

#142

Post by wnoise »

zeven7 wrote: post #104
roryisok wrote: post #3

> "If Newtonian physics can’t predict the fixed curves, perhaps we should fix Newton, instead of making up a whole new class of matter just to fit our measurements." I've always felt this way about dark matter, but as a lay person with no background in physics, it's an opinion I'm hesitant to express. if you have a model that predicts something, but the prediction is off by several orders of magnitude, the model is w…

Part of the problem is that fixing Newton is more than just adjusting the equation; it requires making up a whole new constant , which to some is worse than making up a whole new class of matter. Constants don't have explanations; they're just like saying, "I don't know why it works out this way, it just does." It's better to have a reason that explains why something happens than to throw up your hands and say "let's…

A new class of matter has a whole bunch of constants -- mass, interaction coefficients, mixing angles, etc.

Re: A Physicist Who Denies That Dark Matter Exists

#143

Post by EGreg »

TheHegemon wrote: post #94
EGreg wrote: post #88

Earlier quoted context omitted.

How do we know dark matter isn't just really transparent matter? Like, we can't see it in space but it's there, not reflecting or deflecting enough light for us to detect it.

Like some kind of dark matter?

JUST transparent to light and nothing more

Re: A Physicist Who Denies That Dark Matter Exists

#144

Post by Avshalom »

effie wrote: post #132
Avshalom wrote: post #56

Earlier quoted context omitted.

Also assuming gravity tends to 1/r at galactic distances makes no god damned geometric sense and would require like extra dimensions with funny topology for gravity to be traveling though.

> would require like extra dimensions with funny topology for gravity to be traveling though. Why? I think I can use simple force formula such as F=k/r without any idea of extra dimensions or topology.

Geometrically if a force radiates uniformly it either

A)has infinite density

B)drops off as 1/r^2

We know that gravity drops off as 1/r^2 for all cases except galaxy rotation curves so for it become 1/r for just this specific scale requires that from gravity's perspective the surface area of a sphere usually but doesn't always increase as r^2. Which in turn means it doesn't move through the 3 spacial dimensions that everything else does.

Re: A Physicist Who Denies That Dark Matter Exists

#145

Post by davrosthedalek »

adekok wrote: post #133
davrosthedalek wrote: post #41

Earlier quoted context omitted.

I don't think this is true. Let's assume every matter is our solar system is actually not neutral, but slightly positively charged. For Sun-Earth, let's say this reduces the effective force by 1%. Since both Coulomb and gravitational attraction has the same power law, this fixes the change everywhere, or in other words, you could absorb the change into the gravitational constant. Same goes for making everything 1% le…

That's not how physics works. We've measured the charge of base particles, we know their charge to 8 decimal places. (e.g. for electrons). There is simply no way for the force of electromagnetism to be different at the scale of solar systems. Even MOND is a tiny modification to Newtons laws, and only a modification in extreme circumstances.

I think you misunderstood my post. My parent post argued that a mass-proportional charge imbalance big enough to cause a measurable change in gravitation would have catastrophic consequences for planets. Indeed, this is not true, the effects on the planet are of the same scale, i.e. ridiculously small.

Of course, as I wrote, both laws follow the same power-law, so this can not solve the dark matter problem. Indeed you can absorb it in the gravitational constant.

I also did not suggest that electromagnetism should be different at the scale of solar systems.

A test of the charge equivalence of protons and electrons to 8 digits is by far not good enough to rule this out. You have to probe the proton charge to ~1E-20 for a 1% change of the gravitational effect. This is beyond the reach even for atomic level measurements. More interesting are the bounds on charge conservation.

Re: A Physicist Who Denies That Dark Matter Exists

#147

Post by breadbox »

zamalek wrote: post #39
mikeash wrote: post #23

Earlier quoted context omitted.

Remember the discovery of Neptune? I mean, not directly, since everyone from that time is dead, but.... That's a nice example of a prediction being wrong, inventing an as-yet-unobserved chunk of matter to fix it, and that invention then being correct. Of course, there's a counter-example in the inner solar system in the form of Vulcan. It was invented to explain Mercury's orbit, but the solution ended up being Relati…

I am not a physicist. > Remember that dark matter isn't just some arbitrary fudge factor that gets inserted into the observations to make the numbers come out right. I look at dark matter/energy as a measurement of what we don't know - it is not necessarily matter or energy (although it could be). It is an effect or the sum of effects that we are not aware of. It's almost like the predictions that Mendeleev made with…

> I look at dark matter/energy as a measurement of what we don't know - it is not necessarily matter or energy (although it could be).

Dark matter is called matter because it has mass, i.e. it experiences gravitational attraction to itself and to other forms of matter.

Dark energy is called energy because it acts like radiation, i.e. it has negative pressure.

> Personally, I don't like dark matter because my "hack" alarm bells start ringing. That being said, I also don't know what I don't know.

Your second sentence is far closer to the mark than your first. Dark matter was indeed seen as a hack in the 1930s when it was first proposed, but there is now a large and remarkably consistent body of observations that show its presence. Here's one lay-friendly blog post that briefly describes some of the evidence: https://medium.com/starts-with-a-bang/why-dark-matter-9252bf...

> In that way, it wouldn't hurt if slightly fewer eyes were looking at particle dark matter and slightly more at "non-matter" dark matter.

It's kind of like quantum mechanics at this point. The only reason there aren't more eyes looking at alternatives to dark matter is because we already did that over the last few decades, and the evidence in favor of dark matter kind of became ridiculously overwhelming.

If you want to float an alternative to dark matter at this point, you have to, at the very least, come up with a theory that explains all the things that dark matter explains. (Presumably you would also come up with something that dark matter doesn't explain that your theory does, but one thing at a time.)

Re: A Physicist Who Denies That Dark Matter Exists

#148

Post by vorg »

drjesusphd wrote: post #89
SagelyGuru wrote: post #15

There is another possible explanation instead of dark matter and that is electric charge and currents (plasma flows). Electric force is many orders of magnitude stronger than gravity. So, if the objects in the universe are charged, the repelling force between them could account for the expansion acceleration in a very simple way.

Dark matter is not the same as dark energy.

Dark matter did include dark energy for a while, according to the article...

> starting from the 1980s, the new cosmological dogma was that dark matter constituted a staggering 95 percent of all matter in the universe. That lasted, well, right until the bomb hit us in 1998. It turned out that the expansion of the universe is accelerating, not decelerating like all of us originally thought. Any form of genuine matter, dark or not, should have slowed down acceleration. And so a whole new type of entity was invented: Dark energy. Now the accepted cosmology is that the universe is made up of 70 percent dark energy, 25 percent dark matter, and 5 percent regular matter. But dark energy is just a quick fix, the same as dark matter is.

That makes it sound like dark energy is an offshoot of dark matter, a different type of dark matter that explains an accelerating expansion instead of the extra gravitational effects.

Re: A Physicist Who Denies That Dark Matter Exists

#149

Post by jballanc »

zamalek wrote: post #39
mikeash wrote: post #23

Earlier quoted context omitted.

Remember the discovery of Neptune? I mean, not directly, since everyone from that time is dead, but.... That's a nice example of a prediction being wrong, inventing an as-yet-unobserved chunk of matter to fix it, and that invention then being correct. Of course, there's a counter-example in the inner solar system in the form of Vulcan. It was invented to explain Mercury's orbit, but the solution ended up being Relati…

I am not a physicist. > Remember that dark matter isn't just some arbitrary fudge factor that gets inserted into the observations to make the numbers come out right. I look at dark matter/energy as a measurement of what we don't know - it is not necessarily matter or energy (although it could be). It is an effect or the sum of effects that we are not aware of. It's almost like the predictions that Mendeleev made with…

I was in the same camp as you until the results from the Bullet Cluster were published (https://arstechnica.com/science/2006/08/5058/). Essentially, for the first time astronomers were able to observe the separation of visible and dark matter. In other words, there was evidence for a gravitational force where no visible matter existed.

That said, I think you're wrong about alternate hypotheses being quickly dismissed. Alternatives are regularly proposed and evaluated. Many are eventually found to be lacking in the face of the evidence collected, but some remain viable candidates (for example: https://arstechnica.com/science/2017/01/new-ideas-on-gravity...).

Re: A Physicist Who Denies That Dark Matter Exists

#150

Post by asimpletune »

pharrington wrote: post #111
fader wrote: post #106

Earlier quoted context omitted.

The article does mention this: > In 2004, Bekenstein proposed his TeVeS, or Relativistic Gravitational Theory for MOND. Since then, several different relativistic MOND formulations have been put forth, including one by me, called Bimetric MOND, or BIMOND. > So, no, incorporating MOND into Einsteinian physics is no longer a challenge. I hear this statement still made, but only from people who parrot others, who themse…

Just to clarify, that was specifically what that part of my comment was about. The fact that ctrl+f'ing "reference" finds nothing in that article is rather telling. addendum: If you're going to throw away relativity, step up, stop being a coward: straight up throw away relativity and say Einstein was wrong. Again, you need to come up with some very compelling evidence and a seriously strong theory, but don't weasel a…

Well, what if they were cmd+f'ing?
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