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Showing posts from April, 2014

There is no electromagnetic field - get over it!

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A quick Sunday post on something I've written a little about before. But first, a quote
"Give me a child until he is seven, and I will give you the man" This, of course, has a religious origin, but it applies in many human endeavours.  Including science.

I've taught at a university level for more than a decade, and I've noticed something slightly odd. Namely students coming into university seemed to have some particular fixed notions which you have to work hard at to shift.

There are a number of examples of this, including things like the conservation of energy, which was drilled into them at school but when you tell students that energy is generally not conserved in Einstein's theory of relativity, they initially stare in disbelief.

And when it comes to quantum mechanics, they seem to think that electrons are really little hard balls that sometimes behave as a wave, whereas photons are really waves that sometimes act as particles. Really they need to think o…

The Greatest Experiment you've never heard of!

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This Easter weekend is almost over, and has been quiet as the kids are off at camps. So, I'm going to write about something I think is very important, but many don't know about.

Let's start with a question - what was the greatest year of the last century in terms of scientific discovery?

Many will cite 1905, Einstein's miracle year, which I admit is a pretty good one. Then there is 1915, when Einstein sorted out general relativity. Again, a good year.

But I'm going to say 1956.  You might be scratching your head over this. 1956 was a good year - Elvis recorded Heartbreak Hotel and the Eurovision Song Contest was held for the first time - but in terms of science, what happened?

Well, there was a prediction in a paper and an experiment which changed the way we really understand the Universe. But what's this all about?

The key thing is concept called parity. Basically, all parity asks the question of what the Universe looks like when viewed in a mirror. Again, yo…

Gravitational lensing in WDM cosmologies: The cross section for giant arcs

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We've had a pretty cool paper accepted for publication in the Monthly Notices of the Royal Astronomical Society  which tackles a big question in astronomy, namely what is the temperature of dark matter. Huh, you might say "temperature", what do you mean by "temperature"? I will explain.

The paper is by Hareth Mahdi, a PhD student at the Sydney Institute for Astronomy. Hareth's expertise is in gravitational lensing, using the huge amounts of mass in galaxy clusters to magnify the view of the distant Universe. Gravitational lenses are amongst the most beautiful things in all of astronomy. For example:
Working out how strong the lensing effect is reveals the amount of mass in the cluster, showing that there is a lot of dark matter present.

Hareth's focus is not "real" clusters, but clusters in "synthetic" universes, universes we generate inside supercomputers. The synthetic universes look as nice as the real ones; here's one someon…

The Multiverse is not not the answer!

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With the recent BICEP2 results, the question of the Multiverse has raised it's less than pretty head. The Multiverse is a topic which polarizes people, some who embrace the idea that our Universe is just one of countless trillions and trillions and trillions of other universes out there. Others get a little cross with the popularity of the topic. And then there are those (looking at you slashdot commenters) who generally talk nonsense. Over at Starts with a Bang Ethan Siegal tells us that The Multiverse is not the answer. The essential crux of Ethan's argument is that, in calling on the Multiverse, cosmologists are giving up on science. What does he mean?
The Multiverse is not a single concept, there is more than one kind, but the basic idea is that, as well as our Universe, which we find quite cosy for life, there are a myriad of other universes. These universes are not identical to our own, but possess different physics, different masses of the fundamental particles, differ…