Device creates negative mass?

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Was reading this article:
https://phys.org/news/2018-01-device-negative-massand-lasers.html#jCp

The article claims that these guys have created negative mass? If that's true, isn't that ground breaking? It's one of those extraordinary claims that needs extraordinary proof, doesn't it?

Or is this talking about some sort of analog of negative mass, that isn't really negative mass? Can anyone explain this to me?
 

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  • #2
DrClaude
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Others (@ZapperZ @DrDu) will explain this better, but they created excitons in a semi-conductor that have an effective negative mass.

S. Dhara et al., Anomalous dispersion of microcavity trion-polaritons, Nature Phys. (avance online publication)
Link to the article (appears to be open access): https://www.nature.com/articles/nphys4303.pdf

Dhara et al. said:
The dispersion of the lower trion-polariton branch is completely inverted, which translates to a negative mass for the trion-polaritons in the neighbourhood of ##k_\parallel = 0 ##.
 
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  • #3
Lord Jestocost
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Was reading this article....
The title of the article "Device creates negative mass—and a novel way to generate lasers" is a typical eyecatcher, viz. nonsense. As @DrClaude says, it's the effective negative mass what they are talking about. Nothing mysterious!
 
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ZapperZ
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Was reading this article:
https://phys.org/news/2018-01-device-negative-massand-lasers.html#jCp

The article claims that these guys have created negative mass? If that's true, isn't that ground breaking? It's one of those extraordinary claims that needs extraordinary proof, doesn't it?

Or is this talking about some sort of analog of negative mass, that isn't really negative mass? Can anyone explain this to me?
This has been tackled many times. You might want to start by reading this thread:

https://www.physicsforums.com/threads/physicists-create-negative-mass.911744/

Zz.
 
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Aha, so negative "effective" mass, so just BS?

So we're still awaiting warp drives, and stabilized wormholes in the meantime, I guess?
 
  • #6
ZapperZ
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Aha, so negative "effective" mass, so just BS?
I have no idea what you mean by "BS". It is NOT BS, at least, not in physics terms. What is "BS" is the way news media have portrayed it, and the way many in the public are comprehending it.

Zz.
 
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Nevertheless I agree that that concept of a negative mass is fundamentally ridiculous,
Could there be negative trees or antiplanets ?
 
  • #8
ZapperZ
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Nevertheless I agree that that concept of a negative mass is fundamentally ridiculous,
Could there be negative trees or antiplanets ?
"Fundamentally ridiculous"? Why is that?

The concept, btw, has existed in solid-state physics for as along as we could define effective mass using the dispersion curve E vs k. What people seem to not understand is that this is a MANY-BODY EFFECT, which I've stated a few times and which, I believe, flew over people's head. This realization is the MOST important aspect of this whole thing.

If one can accept that the effective mass of something is a "renormalization" of many-body effects, resulting in what we now know as a "quasiparticle", then there's nothing "fundamentally ridiculous" about this, because this is exactly what we see in terms of the effects of force on an inertial mass (why this is NOT gravitational mass is explained in one of the links that I have given). It is why the electron mass in ruthenates, for example, can be hundreds of times more than the bare mass of an electron. It is why holes have masses.

Having negative effective mass is no more "fundamentally ridiculous" than having spin-charge separation in Luttinger liquids. When these have been experimentally verified, there's nothing fundamentally ridiculous about them.

Zz.
 
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"Fundamentally ridiculous"? Why is that?.
Because nothing of that sort exists in nature, even though it can be modeled mathematically.
If I owe you an apple that is an agreement based on a mathematical concept.
No real negative apples exist
 
  • #10
ZapperZ
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Because nothing of that sort exists in nature, even though it can be modeled mathematically.
Talk about something that is "fundamentally ridiculous". That statement is an example of that. ALL of physics fits that description. That's like saying the standard model doesn't exist "in nature", whatever THAT means.

This effect has been experimentally verified. Period. Everything else is an objection based on a matter of taste or personal beliefs.

Zz.
 
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  • #11
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I have no idea what you mean by "BS". It is NOT BS, at least, not in physics terms. What is "BS" is the way news media have portrayed it, and the way many in the public are comprehending it.

Zz.
Well, that is what I mean by BS, it's not a real particle effect, it's a simulation based on many grouped particles acting like one.
 
  • #12
ZapperZ
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Well, that is what I mean by BS, it's not a real particle effect, it's a simulation based on many grouped particles acting like one.
That's like saying statistical physics is BS because it is all based on simulation. That's silly!

The word "real" is often misused, as if we know what "real" is. If you think an "electron" is real and does not come with a whole mathematical "model" behind it, you haven't learned anything.

Zz.
 
  • #13
Dr. Courtney
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If one can accept that the effective mass of something is a "renormalization" of many-body effects, resulting in what we now know as a "quasiparticle", then there's nothing "fundamentally ridiculous" about this, because this is exactly what we see in terms of the effects of force on an inertial mass (why this is NOT gravitational mass is explained in one of the links that I have given). It is why the electron mass in ruthenates, for example, can be hundreds of times more than the bare mass of an electron. It is why holes have masses.

Having negative effective mass is no more "fundamentally ridiculous" than having spin-charge separation in Luttinger liquids. When these have been experimentally verified, there's nothing fundamentally ridiculous about them.

Zz.
One important thing to look out for in renormalizations and other convenient transformations of specific problems is whether existing laws of physics are maintained. This renormalization violates the equivalence of gravitational and inertial mass. Violating such an important existing law of physics may well be sufficient to describe it as "fundamentally ridiculous." The negative inertial mass is an artifact of the math.
 
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ZapperZ
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One important thing to look out for in renormalizations and other convenient transformations of specific problems is whether existing laws of physics are maintained. This renormalization violates the equivalence of gravitational and inertial mass. Violating such an important existing law of physics may well be sufficient to describe it as "fundamentally ridiculous." The negative inertial mass is an artifact of the math.
If it is an "artifact" of the math, such as the non-physical region in an image charge problem, then it can't be experimentally measured.

What do you think that they got here?

Furthermore, you might as well state the same thing for when we detected the mass of the quasi-electron in strontium ruthenates to be 200x the electron bare mass. Would you like to dismiss the dispersion curve that we have measured for that material as simply an "artifact of the math", or the fact that the material actually BEHAVES that way?

This is not "fundamentally ridiculous". There are MANY fundamental physics that came out of condensed matter. Saw any Majorana fermions lately in particle physics experiment? The fact that renormalized mass came out of many-body interactions is significant, because there ARE theoretical scenarios where ALL of our fundamental particles themselves are "emergent" particles, and that gravitational mass need not be commensurate with inertial mass especially if the concept of "mass" can have a broader definition.

The problem here is that all of this nonsense is ignoring the most fundamental question: how do we define the EFFECTIVE mass of ANYTHING that is inside a solid. If you agree with the current definition (i.e. via the band structure dispersion), but somehow toss away the one shows negative effective mass, despite (i) the physical properties of the material and (ii) the experimental measurements, then it is YOU who have to come up with a PHYSICAL reason for it. Dismissing something as simply be "fundamentally ridiculous" has never been accepted as a valid reason in physics, because this is ancharacterization based on TASTES. It may fly in politics, but not in science!

Zz.
 
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  • #15
Dr. Courtney
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Dismissing something as simply be "fundamentally ridiculous" has never been accepted as a valid reason in physics, because this is ancharacterization based on TASTES. It may fly in politics, but not in science!

Zz.
If the characterization of "fundamentally ridiculous" objective like violating fundamental laws of physics, why can't it be reasonable?

Violating the equivalence of inertial and gravitation mass may well be an issue.

I get that physicists often do this (as in the broader effective mass issue), but then they need to take due care that things are explained adequately for broader audiences who do not have all the details.
 
  • #16
ZapperZ
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If the characterization of "fundamentally ridiculous" objective like violating fundamental laws of physics, why can't it be reasonable?

Violating the equivalence of inertial and gravitation mass may well be an issue.

I get that physicists often do this (as in the broader effective mass issue), but then they need to take due care that things are explained adequately for broader audiences who do not have all the details.
Wait, this is now TWO SEPARATE ISSUES!

If you look at one of the links I gave (which happened to quote one of the "horse's mouth"), there was a great deal given to the fact that the media misinterpreted what has been given to them. And yes, many of us, including those of us on here, have been trying to correct that.

But the other issue, which is a physics issue, is that there is no a priori requirement that inertial mass and gravitational mass have to be commensurate with one another! We only assume that they are because that is what we have seen all along. But we have seen many other things all along that have turned out to be different! There is nothing fundamentally absurd that they might be different. Some people think fractional charge is "fundamentally nonsense". Some people think spin-charge separation is "fundamentally nonsense". And yet, there they are, in broad daylight from many experiments!

Again, I see nothing more than simply personal preferences and a matter of tastes. This is a political argument, not physics.

Zz.
 
  • #17
DrDu
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Basically, if described in many particle language, already a helium balloon has a negative mass. Just define the air surrounding it as the new vacuum state and declare the balloon to be a quasi particle, and voila, you got a particle with a negative effective mass!
 

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