Educarti come un figlio
ad evitare che accada
il solito passo falso
smerciato sul ciglio
della strada
a nulla è valso se la botola
in anello si arrotola
e in questo turno hai più fratelli
di Saturno anelli
di scelte ai lati e satelliti
perché le vie del signore sono infinite:
appena ne esci una
cadi sull'altra luna.
Showing posts with label physics. Show all posts
Showing posts with label physics. Show all posts
Friday, 8 April 2016
Wednesday, 9 December 2015
Quantum Annoyance
Quantum mechanics as a field of science is old. Guys, we are talking of a theory completely developed before 1930 (the main contributors Schroedinger, Heisenberg and Dirac got their Nobel prizes in 1933). Sadly enough, quantum mechanics (qm hereafter) did not receive that much popular acclaim like Einstein's Relativity, mainly because qm wasn't the product of a singular mind, but the joint collaboration of the most brilliant minds of the last century (Einstein too, in a peculiar way).
Only in recent times I've seen an increasing interest, and an increasing misuse, in the word 'quantum'.
The fact that qm is perceived as an interesting topic is good, but the true reason is its mystic nature. And that really pisses me off.
Quantum mechanics, and its relativistic covariant version quantum field theory (qft), is nothing like mystic. It is a theory: a set of laws and rules that describe nature, based on some principles believed absolute.
If you are reading this and you do not know much about qm, then you better know that qm is just the crowning jewel of the human thought and it is a direct evolution of Galilei's and Newton's work. Never in history of science has a theory struggled so much on the meaning of Measurement and Observation. Qm is basically the only scientific theory that embodies in itself the existence of a measurement device inside the system we are describing.
This is an evolution of the concept of Observer in Galilei's and Einstein's Relativity.
Qm looks strange and mystic because for the first time we have a theory which KNOWS that in the end we have to compare to the experiments. It's a huge breakthrough: we do not have a theory constructed in some hyperhuranium, like Plato's ideas, that needs to be dirtied when applied (because every other scientific theory does exactly that).
Qm is strange because it's not shy, qm doesn't lie about the ugly difficult job to understand reality.
Is an electron a particle or a wave? Well it's neither and it's both (that is what experiments tell us!). Qm describes them exactly them as probability distributions! What does it mean? It means that qm can not tell you what an electron is, but can tell you where you can find it, how often and also why you can find it here and not there.
It looks strange, but science is not Tolkien, there is no background story to the characters, only Possibilities.
You may have heard that qm is no more a deterministic theory, but it is probabilistic. In fact qm gives you probabilities that something is somewhere, but you could not find a trajectory for your objects from day zero to the doomsday. In qm there is no fate. Only possibilities.
Can you now see why, as a theory, qm is both appealing and scary?
But in the end this is not Scientology, qm is as it is because people spent nights looking at papers with experimental results. I like to picture in my mind Wolfgang Pauli staring at a blackboard with a cup of coffee the whole night trying to figure out why things went that way.
Think of a physicist as you would think of Sherlock Holmes. You have a crime scene and, no matter how odd your reasoning, you have to connect the dots.
Qm is not fancy or strange by construction, it became the way it is because it's the only way, the only rulebook, that allows us to decode the reality.
This is no alchemy, it is war against reality. And we won this battle.
It is no matter of science, faith, aesthetics or art. That's what i would like the people to understand: qm is just something you should be proud of, as a human being. Nothing to fear, worship or admire. Just be proud of this achievement.
Only in recent times I've seen an increasing interest, and an increasing misuse, in the word 'quantum'.
The fact that qm is perceived as an interesting topic is good, but the true reason is its mystic nature. And that really pisses me off.
Quantum mechanics, and its relativistic covariant version quantum field theory (qft), is nothing like mystic. It is a theory: a set of laws and rules that describe nature, based on some principles believed absolute.
If you are reading this and you do not know much about qm, then you better know that qm is just the crowning jewel of the human thought and it is a direct evolution of Galilei's and Newton's work. Never in history of science has a theory struggled so much on the meaning of Measurement and Observation. Qm is basically the only scientific theory that embodies in itself the existence of a measurement device inside the system we are describing.
This is an evolution of the concept of Observer in Galilei's and Einstein's Relativity.
Qm looks strange and mystic because for the first time we have a theory which KNOWS that in the end we have to compare to the experiments. It's a huge breakthrough: we do not have a theory constructed in some hyperhuranium, like Plato's ideas, that needs to be dirtied when applied (because every other scientific theory does exactly that).
Qm is strange because it's not shy, qm doesn't lie about the ugly difficult job to understand reality.
Is an electron a particle or a wave? Well it's neither and it's both (that is what experiments tell us!). Qm describes them exactly them as probability distributions! What does it mean? It means that qm can not tell you what an electron is, but can tell you where you can find it, how often and also why you can find it here and not there.
It looks strange, but science is not Tolkien, there is no background story to the characters, only Possibilities.
You may have heard that qm is no more a deterministic theory, but it is probabilistic. In fact qm gives you probabilities that something is somewhere, but you could not find a trajectory for your objects from day zero to the doomsday. In qm there is no fate. Only possibilities.
Can you now see why, as a theory, qm is both appealing and scary?
But in the end this is not Scientology, qm is as it is because people spent nights looking at papers with experimental results. I like to picture in my mind Wolfgang Pauli staring at a blackboard with a cup of coffee the whole night trying to figure out why things went that way.
Think of a physicist as you would think of Sherlock Holmes. You have a crime scene and, no matter how odd your reasoning, you have to connect the dots.
Qm is not fancy or strange by construction, it became the way it is because it's the only way, the only rulebook, that allows us to decode the reality.
This is no alchemy, it is war against reality. And we won this battle.
It is no matter of science, faith, aesthetics or art. That's what i would like the people to understand: qm is just something you should be proud of, as a human being. Nothing to fear, worship or admire. Just be proud of this achievement.
Tuesday, 24 September 2013
When you say "classical"
I've noticed an amazing increase of views since my last post on "effective theories".
That's cool, seems there's someone out there appreciating the topic (actually I suppose this mighty viewer came here by chance and still regrets the choice... OK, I don't give a shit 'bout y'all anyway).
What I want to discuss is the "difference between classical and quantum theories" and what I mean by that.
First of all Special 'n' General Relativity are classical. Got it?
Since we are doing science and not oiled-walls-climbing theology, what we are interested in is "measurement".
How do we make correspond the measuring process (in real life) to a (mathematical) action on our (mathematical) model (~theory)?
Remember that in real life we measure real scalars, even when you are measuring a "vector quantity" (what's a vector, anyway?) we do measure component after component. Real numbers (with precision related to there measuring process resolution... ok now don't bring uncertainty relation and stuff. Keep it real, bro), real numbers i was saying: never heard of someone measuring a quaternion.
And here it is:
-Classical: measurement is a function f: V-> R that takes an element (which represents the state of the system under inspection) of the configuration space* V and gives us a real number of R.
-Quantum: measurement is the eigenvalue o of an hermitian** operator O applied on a vector (which represents the state of the system under inspection) of an Hilbert space. Note that eigenvalues of hermitian operators can be only real (even if the scalar field of an Hilbert vector space is the complex field) as a measurement must be.
Better formulations of the theories (or just more suitable for applications) measure average values, transition probabilities and so on. Fuck it, I only gave you a conceptual insight that took me several years (no kidding, bro) to appreciate.
You are welcome.
There are all those subleties about quantum effects and fluctuation, yeah I know, but they invented Path Integral and partition functions for some reason (and discovered the connections between the two quantities, which leads to connections between quantum propagators and statistical correlation functions and, man, this is a blog lemme keep it simple!).
Probably I will enrich, modify or delete this stuff.
Or probably I will write something about classical symmetries (invariance of the action/Lagrangian) opposed to symmetries in quantum Mechanics (Linear Unitary or AntiLinear AntiUnitary operators, Wigner Theorem) and maybe I will write a nice intro on Poincaré group representations and then BANG! Quantum Field Theory!
See ya.
* the space of all q's and p's + time parameter t, usually given n parti les it's a 6n+1 manifold blablabla, in case of continuum degrees of freedom things are not that simple, but you know...
**actually there are technicalities for the boundness blablabla and it should be essentially self-adjoint or something like that
Monday, 23 September 2013
Effective Theories vs illusions
All right, got to learn something about Renormalization. For those who do not know what renormalization is, well, I don't care (http://en.wikipedia.org/wiki/Renormalization).
Anyway, where do you learn Renormalization? Of course on books and articles with titles like "Renormalization". Easy till now.
I stumbled on this article by Joseph Polchinski (http://arxiv.org/pdf/hep-th/9210046v2.pdf) , who happens to be author of one of the best books on String Theory. (Actually it's a two volumes series on Strings, but who cares about details here?).
Here's a quote (from an hypothetical dialogue Polchinski-student) you can find in the linked article:
Student: "Doesn’t all this mean that quantum field theory, for all its successes,
is an approximation that may have little to do with the underlying theory?
And isn’t renormalization a bad thing, since it implies that we can only probe
the high energy theory through a small number of parameters?"
Polchinski: "Nobody ever promised you a rose garden."
That's for all you unbelievers roaming around shouting that "science is soulless". Fuck off and begin learning some science "the hard way".
[As usual: my english may suck but, man, you all don't have better readings?]
Anyway, where do you learn Renormalization? Of course on books and articles with titles like "Renormalization". Easy till now.
I stumbled on this article by Joseph Polchinski (http://arxiv.org/pdf/hep-th/9210046v2.pdf) , who happens to be author of one of the best books on String Theory. (Actually it's a two volumes series on Strings, but who cares about details here?).
Here's a quote (from an hypothetical dialogue Polchinski-student) you can find in the linked article:
Student: "Doesn’t all this mean that quantum field theory, for all its successes,
is an approximation that may have little to do with the underlying theory?
And isn’t renormalization a bad thing, since it implies that we can only probe
the high energy theory through a small number of parameters?"
Polchinski: "Nobody ever promised you a rose garden."
That's for all you unbelievers roaming around shouting that "science is soulless". Fuck off and begin learning some science "the hard way".
[As usual: my english may suck but, man, you all don't have better readings?]
Subscribe to:
Posts (Atom)