DarkMatter/Dark Energy
mile...@templer.net
Oxford. Driving home I realised my uncertainty about the relationship
between dark matter and dark energy.
If I understood you correctly, you said at the outset that 25% of the
universe was missing dark matter and 75% was (?missing) dark energy;
you then made an observation abt the 'equivalence' of energy and mass
- I took this at face value but don't really understand the
implications of this equivalence (except it seems to produce atom
bombs)!
Q1: If CERN, or whoever, find particles which prove the existance of
dark matter, does that mean we are still left with a missing 75% of
the universe's expected mass? Q2: Is matter continually changing
between mass and energy (other than in the centre of stars) or can
cosmologists account for the expected 75% of dark energy?
Lastly and possibly unrelatedly, I know as little abt anti-matter as i
do abt dark matter. Does anti-matter exist, if so does it have mass
and if so is it part of the missing mass?
Thank you
Miles
ps I was the very relieved person at the door asking whether the
lecture was on, when you replied you were giving it! After your
lecture I was wondering whether you had writen the Wikipedia article
on Dark Matter which i thought very good!?
Roberto Trotta
thanks for coming along! I'm glad you enjoyed it.
> Q1: If CERN, or whoever, find particles which prove the existance of
> dark matter, does that mean we are still left with a missing 75% of
> the universe's expected mass?
Yes - the 25% that is (probably) made of dark matter particles will
then be accounted for if and when we actually detect such a new
particle (either by producing it at CERN or by picking up its
signature in one of the underground dark matter detectors). The
remaining 70% (dark energy) is thougt to be of a different nature, and
it certainly has a very different impact on the expansion of the
Univere (making it accelerate), even though there are models that try
to link dark matter and dark energy together.
> Q2: Is matter continually changing
> between mass and energy (other than in the centre of stars) or can
> cosmologists account for the expected 75% of dark energy?
If dark matter is a new type of particle and dark energy is a
cosmological constant (stemming from the energy associated with empty
space), then the two phenomena are unrelated and would not be
converting into each other. However as I mentioned people speculate
that actually this is not the case and dark energy/dark matter are two
sides of the same coin. In this case a new entity is postulated that
would behave partly as dark energy and partly as dark matter and thus
explain both at the same time. However those models are speculative
and suffer from their own troubles.
> Lastly and possibly unrelatedly, I know as little abt anti-matter as i
> do abt dark matter. Does anti-matter exist, if so does it have mass
> and if so is it part of the missing mass?
Antimatter does exist, although only in tiny amounts in Nature. It can
be copiously and easily produced in the lab, though. When antimatter
meets matter, the two annihilate giving off a flash of energy.
Essentially all of the visible Universe is made of matter (if there
were galaxies made of antimatter they would annihilate upon encounter
with matter galaxies), and this is one of the unsolved mysteries of
cosmology, ie why is it that the Universe is made of matter and not
antimatter (or rather, what tilted the original equilibrium between
the two in favour of matter. If you think about it, a Universe with
50% matter and 50% antimatter could not exist because eventually the
two sorts would annihilate each other and there would be no galaxies).
Anitmatter however is of the same type as matter (in particular, it
emits and absorbs light) and therefore it is not a candidate for dark
matter.
> lecture I was wondering whether you had writen the Wikipedia article
> on Dark Matter which i thought very good!?
Not my doing this one! :-)