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A Prelude: Let's say, for the sake of argument, exotic matter comes from exotic places. These exotic places are alternate dimensions/parallel universes, etc., but are accessible via wormholes. Perhaps another being came from these places and ended up in our universe, granting us access to an exotic matter with negative-mass properties. This would give rise to Warp Drives and Worm Hole technologies.

However, the real question is: what would that environment be like? How would we see it? What would be the different "constant" (gravity, for example, from RAFT by Stephen Baxter) for things in that universe (if it applies)? Would we be able to survive there within a spacecraft? How would spaceflight work? What about something from that universe here? What would an organic being be like from that place if it were possible?

Just looking for an idea of some basic observable stuff like something someone would see from a window, the feeling of the spacecraft moving if it were different, effects being in that universe would have on the body, etc.

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Negative mass. Which mass? Consider for instance, force between two charges, force between two masses, and newton's second law: $$ F = -\frac{GMm}{r^2} = ma,\quad\quad F = \frac{kQq}{r^2} = ma,\quad\quad $$

I inserted the electrical force to help us visualize what is going on with the gravitaitonal case: The masses $m$ aren't equal. The $m$ in $GMm$ is gravitational mass, or, comparing with the electrical case, we could call it gravitational charge, which is different from the mass in $F = ma$, which is inertial mass. While inertial mass must be positive in all cases, it could be that there exists some kind of matter with negative gravitational mass.

In our universe, all experimental evidence seems to point out that inertial mass is equal to gravitational mass. This is called the equivalence principle, which states, gravitational and inertial masses are equivalent.


A universe only made of negative mass. This universe would be indistinguishable from a universe made only of positive mass. Let $m_q$ be gravitational mass, and let $m$ be inertial mass, just to be clear about the difference. In this case, we would have:

$$F = -\frac{GM_q m_q}{r^2} = ma,\quad\quad M_q < 0,\quad m_q < 0,\quad GM_q m_q > 0$$

In this case, the product of any two masses is positive, and because the inertial mass of everything is positive anyway, gravity in this world would be indistinguishable from our world.

How about everything else? Well, because inertial mass is always positive, nothing is changed. Consider an electron with inertial mass $m_e>0$ and gravitational mass $m_q = -m_e < 0$. Because $F = m a = kQq/r^2$, inertial mass $m$, it is the same equation in our universe with positive mass, so, everything happens identically.

Negative pressure? No such thing. Pressure of a gas, for instance, is a result of collisions between the gas particles and the walls: they transfer momentum at each collision, whose formula is $\mathbf p = m\mathbf v$, inertial mass. So, the pressure of a gas with negative mass particles would be positive. And because everything is unchanged, they will be able to form chemical bonds, structures, even people.

Would the equivalence principle still work? Absolutely! But we would have instead, inertial mass being equal to absolute value of gravitational mass.

Conclusion: A universe made only with negative mass would be identical to a universe made only of positive mass. No difference, at all.


A universe where both positive and negative masses is present. So let's now consider how things would behave, that had positive and negative mass. Again by using newton's law of gravity, $$F = -\frac{GM_qm_q}{r^2}$$ we see that: alike mass attract, unlike mass repels. That is: two negative masses would attract. Two positive masses would attract. And a positive and negative mass would repel. (just like electrical charges, but, in reverse).

That means three things:

  1. Chunks of positive matter would attract together, and form planets, galaxies and so on.
  2. Chunks of negative matter would attract together, and form planets, galaxies, and so on.
  3. Chunks of negative matter and chunks of positive matter, would repel each other [or, anti-gravitate each other]

So, chunks of positive matter would accumulate together, and repel all the negative matter away with the course of time. Hey. Doesn't that look familiar? We live in a chunk of positive matter after all (positive by convention, anyway).

Would you, a positive mass being, be able to shake hands with a negative mass being? Absolutely! Gravity is such a weak force.... they wouldn't feel anything different.

Of course, there might be some noticeable differences: a cat made of negative mass particles in a positive mass planet, say, Earth, would 'fall up' (on their feet, obviously.. its a cat!).

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Have them be from a negative everything universe so it looks and interacts and looks like this one...except when interacting with the stuff from this universe.

Gravity is easy. Heat flow is too.

One trick thing is the interaction of things like "negative light" with our eyes. Or our light interacting with negative mass. One possible scenario negative light emitting objects cannot be seen because they remove energy from receptors in your eye. But if there was a backlight of positive light behind it, you might see it as a shadow as it dampens the light positive that hits your eye in the same receptors.

Not sure about what would happen if you actually tried to illuminate a negative matter with positive light though. Might have to check on the math to find out if reflection or absorption and emission get all swapped around.

A trickier part is how do you want to deal with something like a ship from this universe moving in space-time of the negative universe. Is the space-time "normal" in both universes? Might be easiest that way so rearward firing engines still push forward work normally. Otherwise it goes off the rails a bit if you have to fire your positive matter ship's engines forward to move forward, but that doesn't make sense either because a positive matter ship firing negative matter thrusters forward does the same thing.

If you have the space-time fabric not be the same it opens other cans of worms too like how pressure of positive matter is supposed to behave in a negative universe.

I also read somewhere non-rigorous that positive and negative matter coming into contact would cancel out and become null due to their energies (or reduce to something with the net negative or positive energy if not the same twin matter I guess?) if different types I guess?). Not like antimatter where energy is released but just null. Zero. So no landing on planets, which is just as well since they would be anti-gravity to you.

You can basically cook up your own plausible logic since so little is known on the subject.

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  • $\begingroup$ A sizable portion of this answer seems to be “I don’t know” $\endgroup$
    – Topcode
    Dec 12, 2021 at 3:24
  • $\begingroup$ @Topcode Indeed. But the title does ask for the environment this negative stuff would be found in. $\endgroup$
    – DKNguyen
    Dec 12, 2021 at 3:25

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