Negative Mass

If something in this Universe had negative mass, would it have a repulsive force instead of gravity ? Would it show a reverse - inertia effect, where it would just keep on accelerating when no force is applied to it ? Can Dark energy ( if it exists) have similar properties ?

Originally posted by siddharthsma

If something in this Universe had negative mass, would it have a repulsive force instead of gravity ? Would it show a reverse - inertia effect, where it would just keep on accelerating when no force is applied to it ? Can Dark energy ( if it exists) have similar properties ?

If a pink elephant lived on the moon, would it still do circus tricks?

No one can anser a question with no basis in reality. There is no such things as negative mass, thus there isn't even grounds to guess as an answer to your question.

If a molecule had negative mass, it would not have an effect on gravity...quite possible strong and weak forces could be 'reversed' making the molecule 'disperse' and literally come apart.

For example, if a cup of water had negative mass, it would just evaporate into hydrogen and oxygen.

But of course negative mass doesnt exist.

Originally posted by siddharthsma
If something in this Universe had negative mass, would it have a repulsive force instead of gravity ? Would it show a reverse - inertia effect, where it would just keep on accelerating when no force is applied to it ?

Assuming a Newtonian model F = G*m1*m2/r² it would only repel matter with positive mass yet attract other matter with negative mass. Upon a fast Google search however, it seems that such a thing would conflict with relativity theory however.

www.daviddarling.info...

Originally posted by Simulacra
For example, if a cup of water had negative mass, it would just evaporate into hydrogen and oxygen.

On what grounds?

Originally posted by Simulacra
If a molecule had negative mass, it would not have an effect on gravity...quite possible strong and weak forces could be 'reversed' making the molecule 'disperse' and literally come apart.

For example, if a cup of water had negative mass, it would just evaporate into hydrogen and oxygen.

But of course negative mass doesnt exist.

that is totally false!

The gravitational force is predominant when you're dealing with big objects.
On the atomic/molecule scale , it's the electromagnetic force which is predominant and which keeps the atoms of a molecule together.

As far as I'm aware, Mass is defined as SOMETHING.

To obtain a negative mass, you'd have to have less than NOTHING,

Which, by all conventional laws of physics....is...quite impossible.

I'd think that, if gravity is conveyed by force carriers called 'gravitons' then there could be 'anti-gravitons', no? I mean, most particles have opposites because of 'super symmetry', no? I can't imagine what its properties would be tho, outside of the nice sensible analysis from simon666 above.

Can anti-matter be considered as a negative mass?

Not too much my playground, but I'd like to have some ideas about it...

[Edit]
Big typo...

[edit on 24-8-2005 by SpookyVince]

Originally posted by SpookyVince
Can anti-matter be considered as a negative mass?

Not too much my playground, but I'd like to have some ideas about it...

[Edit]
Big typo...

[edit on 24-8-2005 by SpookyVince]

nope, for a particle and an antiparticle, mass remains the same but the charge varies

Traditionally mass is defined as a metric of inertia ... historically it has represented a resistance to acceleration. In other words a body at rest tends to stay at rest and a body in motion tends to stay in motion, and the amount of force necessary to accelerate this object is proportional to it's "mass." (i.e. F = ma).

That's classical physics. Quantum physics introduces some quirks, and Einstein's famous E = m c^2 presents a slightly different definition of mass ... one that is instead proportional to energy.

So, you must ask yourself in your world, if you can have negative energy. If you can have negative energy you could have negative mass. You might have to redefine some other things too.

There is on the other hand, such thing as negative temperature. You might enjoy reading about entropy and statistical mechanics.

Originally posted by grad_student
Traditionally mass is defined as a metric of inertia ... historically it has represented a resistance to acceleration. In other words a body at rest tends to stay at rest and a body in motion tends to stay in motion, and the amount of force necessary to accelerate this object is proportional to it's "mass." (i.e. F = ma).

That's classical physics. Quantum physics introduces some quirks, and Einstein's famous E = m c^2 presents a slightly different definition of mass ... one that is instead proportional to energy.

So, you must ask yourself in your world, if you can have negative energy. If you can have negative energy you could have negative mass. You might have to redefine some other things too.

There is on the other hand, such thing as negative temperature. You might enjoy reading about entropy and statistical mechanics.

a negative temperature????!!! that's impossible since the entropy is positive!

Originally posted by ludo182

Originally posted by Simulacra
If a molecule had negative mass, it would not have an effect on gravity...quite possible strong and weak forces could be 'reversed' making the molecule 'disperse' and literally come apart.

For example, if a cup of water had negative mass, it would just evaporate into hydrogen and oxygen.

But of course negative mass doesnt exist.

that is totally false!

The gravitational force is predominant when you're dealing with big objects.
On the atomic/molecule scale , it's the electromagnetic force which is predominant and which keeps the atoms of a molecule together.

Did you even read any of the words that I typed? Not to joke around or anything but did you really read anything that was posted? Maybe your eyes happened to accidently circumnavigate every letter in my paragraph, in which case I could totally understand.

Originally posted by Simon666

Originally posted by Simulacra
For example, if a cup of water had negative mass, it would just evaporate into hydrogen and oxygen.

On what grounds?

On the grounds that if a molecule had negative mass, it would repel each particle, thus denaturing the molecule in the process.

I heard of negative mass a while ago, when a friend of mine and I were pitching a theory to a physics professor at the local university; she mentioned that there were particles called "virtual photons" with negative mass, and although I forget exactly how, that shot our idea out of the water pretty good. A Google search came back with about 124 hits for "virtual photon" + "negative mass"; I don't have time to sort through them now, but they all seem to be at fairly reputable sources (ie not sci-fi per se.)

Saying "there's no such thing" about anything when dealing with theoretical physics is a bad idea; just because it's illogical doesn't mean it isn't true or there isn't at least a theoretical situation where it would be possible. Super string theory states that there are what, 11 dimensions to the universe? Or that there are multiple universes? Something along those lines. That's not exactly "logical" by day-to-day standards, yet it's widely accepted throughout the physics community.

From what I saw in my flipping through the results of the Google search above, grad_student is on the right track: negative energy = negative mass, and it doesn't seem to be impossible. If I'm not mistaken, energy is generally defined as a wave, correct? If so, wouldn't negative energy be a wave that is inverted, much like the graph of -sin(x) as opposed to sin(x)?

If I were up in the atmosphere, I would accelerate and keep accelerating (for this particular usage I wil pretend I cannot reach terminal velocity) because of gravity. Does this mean I have "negative mass"? No, of course not. In order to accelerate something needs a force exerted onto it. Something must provide that force, and transfer it. Like an object impacting it. Or Gravity. Or perhaps the use of Solar Wind to create movement. But remember, without gravity there IS NO MASS. So we have to assume there's gravity to have "negative mass". Meaning that something EXERTS the gravity. Meaning you will go TOWARD this object, eventually IMPACTING it. Meaning you will STOP moving, or go through, and reverse direction, either not encountering drag and doing that forever, or encounter drag and eventually stop. Sorry, no "negative mass" IMHO.

But remember, without gravity there IS NO MASS.

This is not true. It might not have weight but it will have the same mass as it would anywhere else. Mass and weight are not the same thing. Weight is relative to the amount of gravity mass is not.

Originally posted by grad_student
F = ma

[and] E = m c^2

These forumulas are a good way of looking at it, as you note, m = c-squared over E, c is a constant, so a negative E yeilds negative mass. But 'negative energy' is as hard to wrap your head around as Negative Mass. Even by the "simple" newtonian equation, we get m=a/F, so negative acceleration will give us negative mass, bwtf is negative acceleration (actually normally negative acceleration is acceleration in teh opposite direction, but that can't apply here), or Negative Force will do it too, but again, wtf is negative force? An bizzarely, an object with negative acceleration and negative force (hypothetically anyways) in this equation will have.... regular mass!

There is on the other hand, such thing as negative temperature. You might enjoy reading about entropy and statistical mechanics.

I though 0 Kelvin was theoretically impossible to get to as a direct consequence of the uncertainty principal? If that's so that how can negative temperature exist if 0 Kelvin is the point where all motion stops. Or did I miss something somewhere?

Originally posted by sardion2000

There is on the other hand, such thing as negative temperature. You might enjoy reading about entropy and statistical mechanics.

I though 0 Kelvin was theoretically impossible to get to as a direct consequence of the uncertainty principal? If that's so that how can negative temperature exist if 0 Kelvin is the point where all motion stops. Or did I miss something somewhere?

Well I'm assuming that he means that at -X Kelvin, motion would not only cease to progress, but will regress. Theoretical of course.