Modified Gravity vs Particle Dark Matter. The Plot Thickens.

They sit in caves, deep underground. Surrounded by lead, protected from noise, shielded from the warmth of the Sun, they wait. They wait for weakly interacting massive particles, short WIMPs, the elusive stuff that many physicists believe makes up 80% of the matter in the universe. They have been waiting for 30 years, but the detectors haven�t caught a single WIMP.

Even though the sensitivity

The concordance model strikes back

Two weeks ago, I summarized a recent paper by McGaugh et al who reported a correlation in galactic structures. The researchers studied a data-set with the rotation curves of 153 galaxies and showed that the gravitational acceleration inferred from the rotational velocity (including dark matter), gobs, is strongly correlated to the gravitational acceleration from the normal matter (stars and gas),

Dear Dr B: Where does dark energy come from and what�s it made of?

�As the universe expands and dark energy remains constant (negative pressure) then where does the ever increasing amount of dark energy come from? Is this genuinely creating something from nothing (bit of lay man�s hype here), do conservation laws not apply?

Puzzled over this for ages now.�

-- pete best



�When speaking of the Einstein equation, is it the case that the contribution of dark

What if dark matter is not a particle? The second wind of modified gravity.

Another year has passed and Vera Rubin was not awarded the Nobel Prize. She�s 88 and the prize can�t be awarded posthumously, so I can�t shake the impression the Royal Academy is waiting for her to die while they work off a backlog of condensed-matter breakthroughs.

Sure, nobody knows whether galaxies actually contain the weakly interacting and non-luminous particles we have come to call dark

Demystifying Spin 1/2

Theoretical physics is the most math-heavy of disciplines. We don�t use all that math because we like to be intimidating, but because it�s the most useful and accurate description of nature we know.

I am often asked to please explain this or that mathematical description in layman terms � and I try to do my best. But truth is, it�s not possible. The mathematical description is the explanation.