Negative Mass An amusing thought experiment, or the Secret of the Universe? | Hacker News Reader

Negative Mass An amusing thought experiment, or the Secret of the Universe?

triplenine.org

53 pointssmokinn36 comments

Oy.

"To settle the question, I called a well-known astronomer who had recently published an article on gravitational lensing. After a brief explanation of negative mass, I asked him if he had ever seen background galaxies distorted into spokes in the absence of luminous foreground galaxies. He said he had seen the phenomenon, but he said it was caused by "something else." I asked him what else could cause that, but he refused to answer and abruptly ended the conversation. So until someone can explain to me what that "something else" might be, I consider this prediction to have been proven correct."

That's a couple of classic psychoceramic shticks, right there. Unnamed "well-known" scientist who provides evidence to support the hypothesis, and hinting at a cover-up.

I think that last line is even more telling. "I consider this prediction to have been proven correct." Credibility: zero.

And putting the burden of proof of explanations for this probably nonexistent phenomenon on anyone trying to argue the point.

Very interesting thought experiment, and it certainly seems to make some exciting postdictions. However, before accepting it, I would need to see what happens with negative inertial mass. Recall that, unlike electric charges, mass has a second role in physics beyond its interaction with one of the four primary forces. Specifically, it's the relation between force and acceleration. General relativity is founded on examining the connection between gravitational mass and inertial mass. If a body has negative gravitational mass, does that mean that it has negative inertial mass as well? Would this mean that if you apply a force on such a body, it accelerates in the opposite direction?

Also, regarding the astronomer that hung up: maybe he's gotten a lot of calls from pseudo-science cranks, and the author sounded like one on the phone. I can understand not wanting to waste your time on that.

He specifically answers the concern about negative inertial mass!

He proposes that to make negative mass make sense with regard to inertia, the equation F = ma should actually have been F = |m|a.

He does not answer the concern, he just throws down absolute value bars to make all inertia work the same way.

Actually he did answer it. You just didn't like his answer.

Just to explain what might be a tricky point, an equation like F = ma isn't just pulled out of the aether. It's a representation of known and studied behavior.

There is no known and studied behavior of objects with negative mass. There isn't even a rationale for throwing down absolute-value bars beyond "symmetry".

His answer says that negative mass objects are just as hard to accelerate.

As per my response here: http://news.ycombinator.com/item?id=1205011

You have it backwards - you can justify throwing absolute value into the equation if you actually find find evidence that negative mass is just as hard to accelerate as positive mass.

Well look, no one has seen negative mass objects (as far as we know). All he's saying is that this is one way to fix the F = ma equation to deal with negative mass.

I agree that the burden of proof is on him or anyone who wants to run with the idea, but for now its just being proposed as neat, possible idea.

You're reading a speculative blog entry as if it were a rigorous scientific paper and then claiming that he hasn't done the science.

No, I'm pointing out that, contra phaedrus, the concern is not "answered", but instead handwaved.

And when someone starts telling stories about a "well-known astronomer" who has substantiated his hypothesis, he's taken his claim to a higher level than "a neat, possible idea".

Also, E=mc^2 needs to be considered.

I would see two solutions here. (IANAP).

1) Energy can be negative. Not sure what that would mean though.

2) You can do the same trick as he did and do E = abs(m)*c^2.

I would be interested to see what the ramifications of each are.

Reasons I am skeptical: the conclusions have extremely profound implications for physics yet this hasn't appeared on my radar through an established journal.

Reasons this is believable: It answers two major questions I have with the current model.

1. Cosmic acceleration. This has been written off as the result of "dark energy." A total cop out, and worst of all, it violates the laws of thermodynamics since energy is being added to the system.

2. The concentration of positive amounts of mass during early stages of the universe should have created a black hole.

Overall I'm still skeptical, but on the other hand, this is a more believable theory that addresses those questions than I have heard so far. I'm very curious if anyone else thinks it may have merit on this basis. I would also love to know if anyone can independently validate the accuracy of the simulations.

Yes, I think it has merit.

The article says the simulations took 60 hours on a "486/DX-33". That brings back memories. Anyone could rerun the simulations on a modern PC by writing about 50 lines of code and 10 minutes of runtime.

While it is easy to criticize odd-ball theories, I think it is more fun to try to think of tests that might support them or disprove them.

I decided to try just that (with html canvas). Its probably WAY off, but it was fun to mash up. http://thecowch.com/media/demo/index.html

edit: just a disclaimer, im no genius at physics and Ive probably misinterpreted the OP's post or made some other gross flaw in this sim.

The expansion of the universe does not violate energy conservation. Energy conservation says \del_b T^ab = 0, where T is the stress-energy tensor. The metric tensor in Einstein's field equations is covariantly constant (\del_b g^ac = 0), and the cosmological constant obviously isn't going anywhere either, so adding the extra term doesn't have any effect with regards to energy conservation. Any reasonable textbook on general relativity will have a proof of this pretty early on.

IANAP.

Note that pure Einsteinian General Relativity does not conserve energy -- even without a cosmological constant. Sometimes people fake it using tortuous analogies that only hold if their spacetimes are nearly flat, but it fails to hold in the presence of curvature.

The first link on Google for the relevant keywords is http://www.phys.ncku.edu.tw/mirrors/physicsfaq/Relativity/GR..., which lays it out nicely.

The idea of negative|imaginary mass has been studied in more depth, particularly in the context of general relativity. http://en.wikipedia.org/wiki/Exotic_matter

> I asked him if he had ever seen background galaxies distorted into spokes in the absence of luminous foreground galaxies. He said he had seen the phenomenon, but he said it was caused by "something else."

Has someone seen some picture and/or explanation of origin?

My thoughts center not so much on all of the conjecture, but of the concept of negative mass itself. The author asks where it might be, but I think it would be better to ask when it might be. It's likely mass is always positive because time is always positive. We take it that all things in existence have mass; if it doesn't have mass it doesn't exist. The concept of negative mass would imply not only that something doesn't exist - it doesn't occur in time - but it specifically doesn't exist, and impacts the universe in the opposite way it would with positive mass. An illustrative example would be a tennis ball on a table. The tennis ball has positive mass, and relates to the universe in ways we are familiar with. If we said the tennis ball's mass was negative, then we are saying that in the universe on the table there specifically isn't the tennis ball, and not just that it doesn't exist, but it's missing (because we're negative) at that point and time, and the universe is affected proportionally.

How is time positive? All we have in the universe is change in time; right now, 1 second goes by every 1 second, if that makes any sense. So time itself is the integral of this quantity, and because of the +c term, it could be positive or negative.

To clarify, I mean time always goes in one direction: forward.

So you'd say that any object without mass does not exist? Perhaps you'd like to brush up on photons and gauge bosons. The author was no more saying that an object with negative mass is non-existent than a debt is a hole in your wallet. Negative numbers have more meaning than subtraction.

http://en.wikipedia.org/wiki/Massless_particle

Discounting relativistic mass, yes. I'm not sure what the author's specific thoughts on that are; I was only pointing out my view, but your "debt is a hole in the wallet" is actually similar to what I'm proposing. The key is the object doesn't only not exist, it's missing. By the way, whoever upvoted my comment above, good one. It's not easy to wrap your brain around the implication. :)

Wouldn't dark matter provide an alternate explanation for "filament" structure in the universe? The results of the Millenium Simulation seem to fit his qualitative description, and it was run with 10 billion particles, so it's definitely got enough resolution. http://www.mpa-garching.mpg.de/galform/virgo/millennium/

I think the point is that negative mass might be an explanation for dark matter and/or dark energy. Scientists don't really have any explanation for what either of those are -- they're really just "fudge factors" to make the theories fit our observations. To fully understand things, we need to figure out why we need the fudge factors.

All things considered, "someone" could probably toss together a simulation to check the results in well under a week with modern tools, and run it on a modern processor. A modern processor could do much more finely-grained deltas.

Not to mention a lot bigger problem set. 256 points is laughably few nowadays.

No they couldn't. They could just simulate more bodies, but it wouldn't prove anything.

You run a simulation with 1000 times as many bodies. Okay, it looks kind of filamenty. What have you learned?

That the results are robust in terms of your limited simulation. Whether or not it was clear, I was saying that the results of the simulation could be checked, not that therefore automatically he's right about his interpretation of the results.

There is a section on filaments at the very bottom of this page: http://rst.gsfc.nasa.gov/Sect20/A1.html

I think that's what he means by spokes.

http://blog.figuringshitout.com/anything-you-think-is-either...

I would be more convinced if he had shown how he was being unoriginal rather than original.

This is what one of those nerdy, but not actually smart, kids in class went on to do. The others seem to be on HN. If you can't figure out why saying two collections of points "look alike" doesn't mean anything, then it's no surprise you think Outliers makes a compelling argument.

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