# Dark matter and dark energy as a relativistic mass?

According to the theory of relativity, the universe should expand from the center (place of Big Bang) with a maximum possible radial speed close to the speed of light c. So, the galaxies and intergalactic matter moves with a radial speed close to the speed of light too. For instance, this allows to introduce an interesting new idea for the interpretation of the missing mass, dark matter, and dark energy. The current assumption is that the universe contains 4.9% of baryonic matter, 26.8% of dark matter, and 68.2% of dark energy. However, if galaxies and intergalactic matter are moving with the speeds close to c, we should take into account the increase of the mass or energy due to this relativistic speed. The mass which we are observing is related to rest mass m0 and the energy corresponds to peculiar velocities. However, in the models to calculate, for instance, critical density, we should take into account mass increase due to the motion of the baryonic matter mrel = m0/√1/(1-v2/c2). To account for the 95.1% of the missing density, galaxies and intergalactic matter should have speed approximately equal to 99.9% of the speed of light.

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mfb
Mentor
There is no "center" or "place of big bang".

The expansion of the universe is not limited to the speed of light - it is an expansion of space, not objects moving in space.
For instance, this allows to introduce an interesting new idea for the interpretation of the missing mass, dark matter, and dark energy.
No it does not.
we should take into account the increase of the mass or energy due to this relativistic speed.
That does not work.

cristo
Staff Emeritus
There are a couple of incorrect statements in your post. First, the universe is not expanding from a centre, or a point of the big bang. In fact, there is no centre of the universe, and the "point" where the big bang occurred is, in fact, everywhere in the universe.

Furthermore, the big bang is a bit of a misnomer, since it gives the impression that there was once nothing and then, with an explosion, the universe came into existence. This isn't correct. The correct, scientific definition of big bang cosmology is that the universe was once smaller, hotter and denser than it is today, and it has expanded and cooled from that initial state.

Now, this expansion should not be confused with the motion of, say, bound structures through space. It can be thought of as space(time) itself expanding, meaning that these bound structures appear to be moving away from us at some velocity. The further the galaxy (say) is away from us, the faster its recession velocity. Thus, there will be some point far away from us where the galaxies *appear* to be moving away from us at the speed of light, or faster. But they are not really moving at this velocity: that is, locally, there is no violation of special relativity.

There are some frequently asked questions in their own subforum of the cosmology forum that you might be interested in reading.

Thanks