# Dark Matter = Negative mass?

We all know that from the theory of general and special relativity that gravity is just an illusion that a body undergoes when it travels through the fabric of space-time, creating simultaneous depressions, that causes other bodies to be attracted to it.

But, just as a thought experiment, if we compare the force of gravity to one of the other fundamental forces, i.e. the Electro-Magnetic force, we try to think of a kind of a repulsive gravity. My questions it that, could Dark matter, or whatever that is trying to expand our universe be an example of this theory? I mean, could there be negative mass, and I don't means stuff like $-5 kg$. That's irrelevant.

What I want to ask, is if there's something that does all the work and has the same properties of ordinary mass, but repels? I have heard and watched a couple of vids on this topic, and this really is kind of interesting...(for me, at least! :P).

Note by Abhineet Nayyar
5 years, 1 month ago

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@Abhineet Nayyar @Kalpak Shukla What is the probability that negative mass IS dark matter? Could negative mass be claculated via gravitational lensing?

- 3 years, 10 months ago

Hmm, this really IS interesting. I do not consider myself to know anything about space time, So I'll just apply basic Physics here.

So, the fact that this COULD be true has an explanation which goes something like this:

How can space time expand? Imagine spacetime to be a rectangle. Divide it into two parts. Let one be the Dark mass and one be the Non-dark mass and other stuff. Dark Mass : Non dark mass <1

So, one possible expansion reason is that the Dark mass part pushes away the other part,i.e. it repels.

So this does prove that a negative mass exists.

Second is that dark mass may have this property to just Push itself out so that the universe expands.

So, both explanations are possible.

Now we wait unless someone who has immense knowledge on the subject sheds some light on the topic :P

- 5 years, 1 month ago

But wait a second....how do we even know that it is indeed dark matter that causes expansion? I mean we can just see the results and not the causes, can we?

Moreover, even if we could...what would you view as the properties of this negative mass...?

- 5 years, 1 month ago

Well yes. All I'm saying, that if it does, It IS a theoretical possibility.

- 5 years, 1 month ago

The part where people get confused is when it comes to dark matter and dark energy. Dark matter has nothing to do with the expansion of our universe! Dark energy is what is the reason for the expansion of our universe and also is considered to be 70% of what our universe is made. Negative mass is not a possibility because mass is defined as the amount of matter in a particular volume (and no antimatter does not mean matter having negative mass). The term "Dark matter" does not mean that it is somehow opposite of matter. It is termed so as it had gravitational properties and had mass but is not visible by any other means except for the gravitational lensing that it creates.

- 5 years, 1 month ago

The way you defined mass is quite a basic definition. According to relativity, mass is that property of a body which causes gravitational interaction between two bodies. And that, my friend does bring out the possibility of negative mass. It's so hard to comprehend by everyone, because no one expects mass to be negative, but it can be.

The reason we haven't found it is what you just stated, "DARK MATTER DOESN'T INTERACT LIKE ORDINARY MATTER".

- 5 years, 1 month ago

What I am trying to say is 1 - expansion of the universe is due to what we call dark energy not dark matter. 2 - dark matter exhibits nature like normal matter in the case of having gravitational force (which inturn gives Galaxies its structure) and does have positive value of mass as seen in the effect of gravitational lensing which is similar to the results we see in normal matter's (I.e. stars,etc) case. 3 - Existance of negative mass is a hypothesis as of now and it differs in its properties as hypothesised from dark matter.

Hence Dark Matter ≠ Negative mass.

- 5 years, 1 month ago

Wait a second. At one point, you're saying that negative mass is a hypothetical concept, and on the other hand, you're saying Dark matter is not negative mass. How do these two things complement each other??

Second of all, saying that since dark matter shows gravitational lensing is really exaggerating stuff, as whenever we have seen lensing, we have been easily able to associate it with normal matter, so, it might just be that dark matter does not show lensing.

Thirdly, even if it is the dark matter that shows lensing, you can't say that it is negative mass just because ordinary matter shows lensing. It is the same as saying that no black hole exists, those are just stars, because stars show lensing, and we have seen it!

- 5 years, 1 month ago

In my third point I said " Existence of negative mass is a hypothesis as of now and it differs in its properties as hypothesised from dark matter " which means the properties (which are based on the hypothesis of negative mass) of negative matter or the things having negative mass (existence of which is a hypothetical concept as of now) are different than the properties of dark matter that we have seen and calculated from gravitational lensing (Yes dark matter does show gravitational lensing and we have also mapped the clumps of dark matter in the galaxies on the basis of it). Dark matter shows gravitational pull ( like normal matter ) where as negative matter or the things which have negative mass are hypothesised to have gravitational push.

If negative matter (matter which is associated and is supposed to have negative mass) was real and we were to observe negative matter, the results of lensing would not be the same.

You stated "Thirdly, even if it is the dark matter that shows lensing, you can't say that it is negative mass just because ordinary matter shows lensing ". I never said dark matter is negative mass (maybe you were trying to say negative matter), in fact i stated quite the contrary.

- 5 years, 1 month ago

Okay, i agree on the fact that dark matter shows lensing, but how can you say, that it is actually dark matter??

You do know that we calculate the amount of dark matter by calculating the amount of lensing seen in various galaxies and stuff, right? How come we know that this is not due to a very dim celestial object which does not emit any radiation for us to detect. That's not impossible, is it?

- 5 years, 1 month ago

nobody knew $i$ few centuries before us :P

- 4 years, 2 months ago