## Saturday, April 17, 2010

### More is Different

[...The main fallacy [of] the reductionist hypothesis [is that it] does not by any means imply a “constructionist” one: The ability to reduce everything to simple fundamental laws does not imply the ability to start from those laws and reconstruct the universe. In fact, the more the elementary particle physicists tell us about the nature of the fundamental laws, the less relevance they seem to have to the very real problems of the rest of science, much less to those of society.
..]

Anderson, P.W., "More is Diffent" in Science, 1972 177(4047)

## Monday, February 15, 2010

### Everything is relative..... Not!

This is for all of the people which, when they want to say that "anyone can say whatever and it doesn't matter..." say "Everything is relative..." and quote Albert Einstein's Relativity...

Ok listen, this is wrong!

Einstein Relativity theories (special and general ) have been built with the exact opposite aim in mind.
The main idea under the Relativity is the following: take two observers of a physical (chemical, human... whatever) phenomenon, even if they move one with respect to the other at incredibly high velocity or accelerate strongly, they will still be able to describe this phenomenon with the same laws of nature! Ok, the form of the equations will be different... (and probably in order to agree on the numbers they should have a deep Physics knowledge...) but still they will be able to predict the evolution of the system and come to the same conclusions!
Ok, I admit that the word "relativity" is misleading, but please do not cite Einstein for that... he is becoming more wrongly quoted than Jim Morrison...
Hey, everyone can still think and say whatever and it doesn't really matter!, but the Relativity theories teach you a deeper lesson "No matter where, when, how fast or how pushed or pulled you are, we agree on the fundamentals laws of nature! They are what they are, not opinions!"

a popular introduction written by the Einstein himself and freely available on the web.

## Saturday, February 6, 2010

### Best Physics equation ever

If you google "greatest equation ever", you may find many pages and discussions on this topic.
Usually Maxwell equations (which describe the electromagnetic field) are considered the "best" Physics equations ever. In mathematics, Euler's identity e^(ipi) + 1 = 0 has been voted as the most important equation.
Now, first of all it is hard to say what actually "best" means. Here I will define "best" not as the most beautiful, nor the most difficult to derive, nor the one which has given more practical results... I simply consider one of the equations that better represent the "state-of-art" in Physics.

Some days ago I was looking at this formula
T=\frac{1}{8\pi M}\,,

Which is the temperature of a Schwarzschild black hole (M being the black hole mass). I guess I have seen that formula thousand of times in the last year, and never though it was eligible as best physics formula ever... However there is a trick: the formula above is written in "God-given" units, the ones that theoretical physicists and lazy students like more.. In God-given units the speed of light c, Newton constant G, Boltzmann constant k and also Planck constant h, are set to unit.
Restoring more physical units, the same formula above reads
T=\frac{\hbar c^3}{8\pi G M k_b}\,.

And now it looks more appealing, doesn't it? This formula has inside nothing less than almost all the Physics we know. Of course Newton constant is there, after all black holes are gravitational objects... but also Planck constant is there, meaning that black hole temperature has something to do with quantum physics. Einstein's special relativity has its own place there, via the speed of light, c. Finally, we are talking about temperature, we also have Boltzmann constant, k.
Why is this formula so important? Well, for a technical point of view that is because it represents the fact that black holes are not "totally black", but instead they emit thermal radiation (called Hawking radiation, from the theoretical physicist Stephen Hawking who discovered that) with that temperature T.
But the very relevance of this formula lays in the fact that it contains both General Relativity (via c and G) and quantum physics (via h bar).... so it represents the bridge between these very different (?) worlds in Physics, which do not like talking to each others. But that is the topic for another post...