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Physics Forums Featured Threads
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First Human Embryos Edited in U.S.
"Researchers have demonstrated they can efficiently improve the DNA of human embryos. The first known attempt at creating genetically modified human embryos in the United States has been carried out by a team of researchers in Portland, Oregon, MIT Technology Review has learned. The effort, led by Shoukhrat Mitalipov of Oregon Health and Science University, involved changing the DNA..." -
Should Algebra Be Required At Community Colleges?
The chancellor of the California Community Colleges system believes that students who are not majoring in math or science should not have to take intermediate algebra to earn an associate degree. California has the largest community college system in the US, and what goes in California sometimes spreads across the country. What do you think? -
Is it possible to detect a single phonon?
Is it possible to detect a single phonon? If yes, can it be detected at a well-defined position? -
A Poor Man's CMB Primer. Part 5: Quantum Seeds
The CMB establishes a record of ancient acoustic oscillations in the baryon-photon plasma. We’ve been studying how these primordial sound waves evolve, and how to analyze the last scattering surface to learn about them. Now it’s time to confront their origin: what process composed the cosmic symphony? A few different proposals have been advanced over the years to explain the origin of the primordial perturbations. -
Great Magic Triangle Math Puzzle
"The missing square puzzle is an optical illusion used in mathematics classes to help students reason about geometrical figures; or rather to teach them not to reason using figures, but to use only textual descriptions and the axioms of geometry. It depicts two arrangements made of similar shapes in slightly different configurations. Each apparently forms a 13×5 right-angled triangle, but one has a 1×1 hole in it." Can you figure out an easy way to inspect it? -
A propagating Majorana mode
"In a discovery that concludes an 80-year quest, Stanford and University of California researchers found evidence of particles that are their own antiparticles. These 'Majorana fermions’ could one day help make quantum computers more robust." - Stanford News -
Results shown at EPS
The EPS conference was a week ago, and many new results and future plans were shown. A good general overview has been collected by Paris Sphicas in his Summary slides. I had a look at some presentations and collected things I personally found interesting. Warning: The selection is heavily biased, I cannot cover everything, and I probably missed many interesting things. -
Super p-Brane Theory Emerging from Super Homotopy Theory
What are even the principles of the theory? Two principles worth considering: The gauge principle: No two different things are ever equal, instead they may be related by a gauge euivalence. Consequently, no two different gauge transformations are ever equal, instead they may be related by a gauge-of-gauge equivalence. And so on.Mathematically this is the principle of homotopy theory... -
An Integral Result from Parseval's Theorem
In this Insight article, Parseval's theorem will be applied to a sinusoidal signal that lasts a finite period of time. It will be shown that it necessarily follows that ## (\frac{\sin(2 x_o)}{x_o})( \frac{\pi}{2})=\int\limits_{-\infty}^{+\infty} \frac{\sin(x-x_o) \sin(x+x_o)}{(x-x_o)(x+x_o)} \, dx ##. -
Hamiltonian in Quantum vs Classical
The Hamiltonian in classical mechanics is not always equal to the total energy of the system. I believe this is only true if there is only a potential field and no vector potential. However, in quantum mechanics for a particle in an EM field, even if a vector potential is used the energy operator E -> H. Is this an inconsistency? -
Is Biomass Carbon Neutral?
About 9% of Germany's power is produced by wood biomass burning, second only to wind in their "renewable" sector. Clearly, wood can be "renewable", but to me the more important question is: is it green? It appears that the EU considers biomass to be "carbon netural" and thus subsidizes it as a clean, renewable energy source. But the situation is not so clear in the US and there is debate about the issue (sources below)... -
Solar system's path in the Milky Way galaxy
My understanding: Circuit is ~ 30 million years. Plane of solar system orbit is tilted from plane of milky way.
Is milky way plane crossed once or twice? What is error bar for 30 million? How much does dark matter density vary along solar system path? -
Counting intersections of lines in a triangle
Divide each side of a triangle into n equal lengths. Connect the ends of each length to the opposite vertex with straight lines, thereby forming 3n overlapping triangles of equal area. (The problem at the link is an example with n=3.) At how many points will three lines intersect? -
Double field theory: Where is the extra space?
Double field theory [1] is an attempt to realize T-duality of string theory at the level of field theory. For instance, if a field in ordinary field theory lives in 4 non-compact space-time dimensions, then a field in double field theory lives in 8 non-compact space-time dimensions. I don't understand it from the physical point of view... -
The Sleeping Beauty Problem: Any halfers here?
The sleeping beauty problem is a well known problem in probability theory. Allegedly, there are many "thirders" who think that the correct answer is 1/3, but also many "halfers" who think that the correct answer is 1/2. For me, it is quite obvious that the correct answer is 1/3. Is there anybody here who is convinced that the correct answer is 1/2? If you are one of them, what is your argument for 1/2?
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