Negative Mass

[kmMango]

So, I did some thinking recently on negative mass, and I was struck by an interesting concept. At risk of sounding stupid, here it is:

What if Negative Mass not only exists, but perhaps in equal quantities to matter? This would lead to a few weird consequences.

I try to think of it as an electric field equation, where gravity can be positive or negative. I know there is no evidence of this, but bear with me. If that were the case, the net gravity of the universe would be zero.

Let's go to the Big Bang. In a singularity like the one the universe started from, no matter could exist. Only energy would be present, and as the universe expanded and cooled, it would condense to matter. This means you would have a random distribution of positive and negative mass. There would be clumps, irregularities in the distribution. The opposite particles would push away from one another, forming clusters of matter and negative mass. Much like the voids and filaments that make up the large scale structure of our universe.

Negative mass has another consequence. The net gravity of the universe in this scenario would be zero. This means the universe would continue expanding forever. With radiation pressure, wouldn't it also accelerate over time?

I know this is probably wrong. Will somebody more experienced with physics tell me if this is wrong, and if so, how, or if it is possible?

[*Aqua*]

Afaik there is no anti-gravitation. If gravitons exist they are their own anti-particles. It's like light particles which are also the own anti-particles. There can only be positive numbers, no matter what you do.

[kmMango]

Ok. I've heard so many different things on negative mass, I was fairly certain I would mess something up. I just thought it was an interesting consideration.

[K^2]

You are thinking of mass as a real value in Newtonian Mechanics. That's not how mass behaves in real physics. In field theory, mass behaves as a length. Specifically, it's the length of the 4-momentum vector. In natural units p_μp^μ = m². Can you put a negative value in there? Sure. But it's irrelevant. The relevant quantity is m², which ends up being the same sign regardless of whether m is positive or negative.

But what of the gravity, you might ask. Nothing. It has nothing to do with mass. Gravity is determined by the quantity called the stress energy tensor, which tells you how much energy and momentum is concentrated in a point in any coordinate system. And from that, you can work out the amount of mass there, but same amount of mass can have different gravitational effects depending on the state that mass is in. Ultimately, mass itself doesn't determine anything.

So questions of "negative mass" are absolutely silly. Whether you picture mass as positive and negative or all positive, the universe stays exactly the same. Negative energy, on the other hand, that has interesting implications.

[kmMango]

I just mean any form of matter or energy that is gravitationally repulsive. If negative energy is the proper term for that, ok.

In my mind, this would explain the additional gravitational forces attributed to Dark Matter, and the accelerating expansion of the universe we ascribe to dark energy. No evidence of gravitons has appeared, and it seems to me that negative energy would "cancel out" gravity waves if it exists in equal quantities.

[Sirrobert]

Let's go to the Big Bang. In a singularity like the one the universe started from

The universe didn't start from a singularity

[kmMango]

Yeah, I guess it couldn't. Something fairly close to one though. Very dense, very hot.

Edited February 7, 2015 by kmMango

[Sirrobert]

No, the Big Bang is not what you seem to think it is

[kmMango]

Thank you. I knew the "Stretch" happened everywhere, but I think this is beside the point. Even if space wasn't a point, the early universe was too dense and hot for matter, at least so far as we know. Can we agree on that?

[K^2]

I just mean any form of matter or energy that is gravitationally repulsive. If negative energy is the proper term for that, ok.

The net effect of all stress-energy in universe is actually repulsive. The universe is inflating at an accelerated rate. But everything points to pressure terms providing repulsion, rather than negative energy.

[Tommygun]

This is a bit off topic, but is negative energy part of the multi universe theory?

[cantab]

Purely considering classical physics, a negative mass moves in the opposite direction to an applied force. This means that charged negative-mass particles would clump together electrostatically, easily overcoming their gravitational repulsion. I'm not even sure what the nuclear forces would do, but whatever happens you're going to get dense balls of negative mass and high net charge.

These, though, would then attract positive mass particles of opposite charge. From a distance, that would reduce both the net mass and net charge of the agglomeration.

I wonder if the end result wouldn't be something that has zero net mass and zero net charge, despite being full of particles of both signs of mass and charge.

(On a sidenote, as far as gravity is concerned then assuming gravitational and inertial mass are equivalent, a positive mass attracts all masses, while a negative mass repels all masses. This is unsurprising considering general relativity's view of gravity as a distortion in spacetime that thus affects everything equally.)

Edited February 8, 2015 by cantab

[zekes]

Well i know zero mass is possible, in KSP. Just cut some of that off and you get negative mabye?

[PB666]

Thank you. I knew the "Stretch" happened everywhere, but I think this is beside the point. Even if space wasn't a point, the early universe was too dense and hot for matter, at least so far as we know. Can we agree on that?

Space-time during the inflation was messed up, the stretch co-occurred with inflation, but the limits of inflation are unknown. There is a wiki article that has placed various sizes on the Universe and some constraints on sizes based on interpretation of physics.

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

There are issues, one of them being that changes from the end of CMB to present can greatly change age.

[PB666]

The net effect of all stress-energy in universe is actually repulsive. The universe is inflating at an accelerated rate. But everything points to pressure terms providing repulsion, rather than negative energy.

A quick answer to this statement. There is nothing pointing at the origins of dark energy, it is a virtual unknown in our universe. I should point out that mass is derived from energy, therefore any energetic centroid force should be attractive unless its repulsive character can be detected. Thus the dark energy may be attractive in nature, but the nature of that energy is unknown.

Dark energy was hypothesized to explain why a universe that inflated, then slowed expansion, has started accelerating its expansion. The observation has been verified, but it still may not be perfectly characterized.

On a second line of thought......there are physicist that have set the size of the universe at 46.6 billion light years in size. I don't necessarily subscribe to this figure, but a number of physicist believe that inflation had constraints particularly at its end when quantum forces governing the early phase gave rise to relativistic forces that resulted in the material universe. I personally don't think that CMB studies are defininative enough to define the end of the opaque period to that level of precision, the relativistic issues during the period have such a profound affect on relative inertia that this could be off by factors. A critique of any science is based on observable facts, Occam basically argued why create convoluted arguments when simple ones will due. In deference to Occam i think that we limit the Universe size to what which is consistent with the razor.

According to theory however the universe contracts if its mass-energy equivilience exceeds a certain value, otherwise it expands. Since it is expanding it should be less than the value, and since we know the energy density then the size 13.8 billion years ago can be estimated and the size of the inflation can be estimate. If the reason the Universe is expanding is due to negative energy or bubbles sending out gravitational waves to our region of our universe, then the size of the inflatron could've been bigger. The keep point about pre-CMB events and dark-energy is they are veiled entities that are not observable.

The essential problems with multiverses and string theory is that they rely on a set of observations and physics that are unavailable either due to technological limits or intrinsic opaqueness of our material world beyond a certain scalar frame. The current standard model is completely happy without either, but given a universe, expansion, constant CMB the model of cosmic origin is not happy without inflation.

I can make a similar analogy between creation and evolution (though it will probably bother folks). I can argue that evolution exists because we can observe it now and its past events. However there comes a time in life history where the tools that we use to define evolution cease to explain earlier processes. Prior to these there is only speculation how evolution occurred and creation is a possibility. But this might only defer the problem, since that which created may have also needed to have been created (just as we create new life in the lab).

If the fingerprint of the creator is not imbedded in the created then it is almost impossible to resolve the issue more intelligibly and the argument is more or less academic. ......The common problem of origins is that as branches eventually condense into critical transition points, and what happens before the transitions is masked by the branch itself, you need other branches to look into the problem further, but with our visible universe there will always only be one perspective that we can use.