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Archive for the ‘physics’ Category

Things flying in compressed air

Posted by Ed on November 12, 2016


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Introduction to Quantum Computing

Posted by Ed on February 19, 2016

Quantum Computing for the determined
This is a series of 22 videos by Michael Nielsen.
After these videos you can watch this talk given by him.

The topics range from the qubit, quantum gates, superdense coding to quantum teleportation. To understand the lectures I’d say you should have had some exposure to quantum mechanics. In particular you should know about complex numbers and matrix multiplication.

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Toys in Applied Mathematics

Posted by Ed on February 20, 2014

Watch this great talk by Tadashi Tokieda presenting some surprising phenomenona in toys. This is quite fun to watch.

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Vein Viewer

Posted by Ed on February 4, 2014

Watch this marvelous device that lets you view your veins. It almost looks like an x-ray vision. When I first watched the video I thought this was only a gimmick but it really exists.

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Feynman Lectures Book online

Posted by Ed on November 8, 2013

Here is something every Feynman fan will be happy with. The Feynman Lectures book is online. Currently it is only volume 1 but they are hoping to publish volume 2 and 3 as well.


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Cartoon explanation of Higgs boson

Posted by Ed on July 7, 2012

Recently there has been some media coverage on the possible discovery of the Higgs boson. Here is the best explanation on the Higgs particle and the standard model. The video consists of explanations by physicist Daniel Whiteson and drawings made by Jorge Cham who is known for phdcomics:

Here is another nice explanation by Fermilab scientist Don Lincoln:


Here is an explanation using sugar and ping pong balls:

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The sound of hydrogen

Posted by Ed on January 20, 2012

Henry Reich has a series of videos on physics and mathematics each lasting for a minute on his channel minutephysics. He explains topics by using handdrawn pictures and makes them look like an animation. Here are a couple of his excellent videos (among them one that explains how to create the sound of hydrogen):

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Great lectures in honor of Feynman

Posted by Ed on January 14, 2012

Caltech organized an event called TedxCaltech in honor of Richard Feynman. They invited speakers to talk about the person ‘Feynman’ and his work. Among them are Leonard Susskind, Michelle Feynman, John Preskill and many more. The talks are excellent.


The complete list of talks can be found here: TedxCaltech: Feynman’s Vision, the next 50 years

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More on Bell’s Theorem

Posted by Ed on January 6, 2012

In a previous post I shared some links with easy explanations on Bell’s theorem. Here, I want to continue although the explanations are more technical and require more knowledge:

11) Nonlocal correlations between the Canary Islands
This is an excellent blogpost on the blog BackReaction. It discusses the role of nonlocality in Bell’s theorem, in particular the locality loophole and the freedom-of-choice loophole.
Prerequisite: Understanding of light cones. Here are some practice questions on light cones.

12) Is the moon there when nobody looks? Reality and the quantum theory
This is a very intuitive article by David Mermin. He introduces machines that have 3 settings and two lamps (red and green) and shows that assigning 3 “real” properties to particles results in a contradiction.

13) Spooky Actions At A Distance?: Oppenheimer Lecture
A lecture by David Mermin on EPR and Bell’s theorem. Here, he uses three entangled particles (see Greenberger–Horne–Zeilinger state) instead of two. I recommend watching this lecture after you have read 12).

14) Bertlmann’s socks and the nature of reality
by John Stewart Bell
Here, John Bell derives the d’Espagnat inequality by considering socks that may or may not survive one thousand washing cycles at 45°C, 90°C and 90°C.

The d’Espagnat inequality is: N(A,notB)+N(B,notC)≥N(A,notC)
Bell mentions that this is trivial: Each member in N(A,notC) on the right hand side either doesn’t have property B and therefore is in N(A,notB) or has property B and therefore is in N(B,notC). Thus, the left hand side cannot be less than the right hand side, in other words the left hand side is greater or equal than the right hand side.
Note: When you read the document don’t wonder about the figures. They are not missing but shown in the end.
By the way, Reinhold Bertlmann was a colleague of John Bell at CERN. He is a professor now and still seems to wear differently coloured socks.
Bell’s original paper (see DrChinese’s site) becomes much more understandable with this document.

15) Part 1 – From Bell’s Inequalities to Entangled Qubits: A New Quantum Age?
This is a talk by Alain Aspect who conducted some experiments on Bell’s theorem. There are five parts.

16) Hidden variable – Derivation of line
In his talk Alain Aspect shows that one can construct a hidden variable theory that predicts a line for the expectation value. An easy to follow derivation can be found in Quantum theory: concepts and methods by Asher Peres on page 161-162.

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Bell’s theorem easy explained

Posted by Ed on December 21, 2011

Bell’s theorem states that quantum mechanics is not compatible with a theory of local hidden variables. In other words quantum mechanics can not both be (i) local and (ii) realistic (see also the wiki entry on principle of local causality) where with realistic I mean Counterfactual definiteness. Here are a few sites with an easy to understand explanation of Bell’s theorem.

1) Spooky Action at a Distance – An Explanation of Bell’s Theorem
by Gary Felder
This article is easy to understand and only basic mathematics is used.

2) Does Bell’s Inequality rule out local theories of quantum mechanics?
Updated May 1996 by PEG (thanks to Colin Naturman).
Updated August 1993 by SIC.
Original by John Blanton.
This article is more Read the rest of this entry »

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