Physicists create 'negative mass'?

[Greg Bernhardt]

Washington State University physicists have created a fluid with negative mass, which is exactly what it sounds like. Push it, and unlike every physical object in the world we know, it doesn't accelerate in the direction it was pushed. It accelerates backwards.
from - https://phys.org/news/2017-04-physicists-negative-mass.html

Now this sounds interesting! Is this really "negative mass" or is that marketing spin? Thoughts?

Paper: https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.118.155301

 

[Comeback City]

To create negative mass, the researchers applied a second set of lasers that kicked the atoms back and forth and changed the way they spin. Now when the rubidium rushes out fast enough, if behaves as if it has negative mass."Once you push, it accelerates backwards," said Forbes, who acted as a theorist analyzing the system. "It looks like the rubidium hits an invisible wall."

Always a catch... dang it. Still interesting though!

 

[ZapperZ]

I covered a news report on this yesterday:

https://www.physicsforums.com/threa...reporting-comments.897038/page-5#post-5742725

Note that this is the effective mass. The whole concept of "negative effective mass" isn't new. Those of us who took intro Solid State Physics classes have seen these due to the way effective mass is defined.

What is new here is that they detected this in a superfluid system. But considering that there is now a smooth connection between BE condensate and BCS system (thanks to the work of the late Deborah Jin), it is not unexpected that one can have a dispersion in a BE condensate that can produce such negative mass.

Zz.

 

[sophiecentaur]

So no Hoverboards, just yet.

 

[Chestermiller]

I don't know, but I'm interested in anything like negative mass that can help me lose weight.

 

[DrStupid]

"[...] it doesn't accelerate in the direction it was pushed. It accelerates backwards."

That means that a force between this fluid an object with a corresponding positive mass would accelerate both in the same direction. I'm sceptical until I see such an experiment.

 

[AgentCachat]

"Negative mass"? Makes no sense to me, but then neither does quantum mechanics.

 

[ZapperZ]

An air bubble is water has negative mass. One can easily renormalize the mass so that the water surrounding it has zero mass. This is no different than what is done in QFT, resulting in positive holes in semiconductors.

One must pay attention to the background information here. These are many-body effects, the same effect that gives electrons in solids an effective mass that can be hundred of times more than the bare mass! In other words, such effects are already extremely common in the modern electronics that you are currently using!

Zz.

 

[Biker]

Does it behave exactly like "negative mass"? Or is the term just for news?

You can't make hoverboards with it, can you? because If Newton's gravitational law still holds, Then it would accelerate downward as any positive mass object.

Interestingly, What would happen if you place two identical objects with the same magnitude of mass but with opposite signs in space. They will just keep accelerating forever(Newtonian). It won't violate conservation of energy or momentum. I think my mind has just gone Kaboom. Can't you use that to reach nearby stars faster?

 

[Comeback City]

An air bubble is water has negative mass.

Negative effective mass, yes?

 

[houlahound]

Wonder if models of the early universe could utilise this physics re inflation?

 

[Nugatory]

"Effective" is the third word in the PRL abstract: "A negative effective mass..."
Anyone want to find the first appearance of the word "effective" in the phys.org piece?

Just sayin'...

 

[davidge]

Could this negative mass have anything to do with dark energy? Or the vacuum temperature considerable above of absolute zero is already an indicative that it's not the case?

 

[LoganNagol]

<Moderator note: moved from separate thread>

So I have a question about negative mass:

does the equation "k=1/2mv^2 " still apply to negative mass? If it did, does that equal to negative energy? If it does not lead to negative energy, does that mean absolute value bars need to be added to the equation?

I'm using "k=1/2mv^2" for an example, of course my question apply to all energy equations that use mass.

 

[DrStupid]

does the equation "k=1/2mv^2 " still apply to negative mass?

In classical physics, yes.

If it did, does that equal to negative energy?

Yes.

 

[CWatters]

When i saw the news article i wondered how conservation of momentum worked out? For example if you push something away from you and it accelerates towards you then to maintain conservation of momentum don't you also have to accelerate towards the object? Its as if the negative mass of the object somehow gives you negative mass as well?

 

[DrDu]

When i saw the news article i wondered how conservation of momentum worked out? For example if you push something away from you and it accelerates towards you then to maintain conservation of momentum don't you also have to accelerate towards the object? Its as if the negative mass of the object somehow gives you negative mass as well?

There are two kinds of momentum, "true" momentum and effective momentum, the latter one being also called "crystal momentum" for the more specific case of particles moving in a crystal.
E.g. for an electron moving in a crystal, the effective mass can be negative as upon acceleration, the electron is reflected more strongly from the crystal lattice. While the effective momentum may also be negative, the total momentum is conserved, as momentum is transferred to and carried by the crystal.

 

[ShayanJ]

http://backreaction.blogspot.com/2017/04/no-physicists-have-not-created-negative.html

 

[Lwadz88]

So are we talking alcubieere drive or no? Us trekies get excited when we hear negative mass...

 

[Nugatory]

So are we talking alcubieere drive or no?

Not even close. Sorry.

 

[ZapperZ]

I'm probably reviving something that should be left for dead, but in the July 2017 issue of APS News (Pg. 4), there is an article on this, specifically referring to the type of news coverage that some part of the media used to report on the work.

The phenomenon is subtle, and some news sources inaccurately described the paper as heralding the advent of a fluid with “negative mass.” Some headline writers, connecting the results with warp drives, antimatter particles, and the end of “physics as we know it,” had many physicists wagging their fingers.

“Undeniably, a number of news outlets sensationalized the results,” Peter Engels and Michael Forbes, senior researchers on the experiment, told APS News. “[This was] mostly due to a confusion [with]mass ... and the incorrect implication that our fluid could exist in empty space ... ”
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.
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How to define mass, and the difference between “negative mass” and “negative effective mass,” was a topic that Engels and Forbes often had to clarify to reporters. Creating a fluid with “negative mass” is technically correct, they said, but only if “mass” is interpreted in a specific way.

“One main confusion by some of the media was interpreting the term ‘negative mass’ [as] negative gravitational mass, which indeed could have drastic consequences,” Engels and Forbes said. The correct concept is the “inertial mass,” they emphasized, which is what we think of in Newton’s second law: If you push an object, how does it accelerate? In fact, all inertial masses are “effective masses” by definition, since the term describes what someone actually observes.

So there, this is directly from the "horses' mouths", so to speak, something which these media outlets should have consulted from the very beginning BEFORE they sensationalized the story. These concepts were the same ones that have been mentioned in this thread from the very beginning.

Zz.

 

[Comeback City]

So there, this is directly from the "horses' mouths", so to speak, something which these media outlets should have consulted from the very beginning BEFORE they sensationalized the story.

I've noticed that sometimes things don't happen because they make too much sense...
This is one of those cases.