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Physics Forums Featured Threads
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Inconsistency versus lack of knowledge
In traditional logic, a system is inconsistent if it can lead to a contradiction. Furthermore, if the inconsistency is non-explosive (not all consequences follow from the contradiction), then the system is para-consistent.
Both definitions fail to distinguish between the following two real-world scenarios... -
Measurement of Earth's Mass - with Neutrinos
At very high energies Earth absorbs a relevant fraction of neutrinos passing through it. Experiments receive more of these neutrinos from above than from below and the difference depends on the mass of Earth. So why not measure it?
Neutrino tomography of Earth
The uncertainty is very large, of course. While the result is very close to the number from gravitational measurements they have a 25% measurement uncertainty. Larger datasets and KM3NeT will help reducing the uncertainty. While unlikely, Earth might have accumulated something dark matter like - it would appear in gravitational measurements but not necessarily in neutrino absorption data.
Apart from the overall mass they also measure the density in different regions of the interior of Earth and confirm that the core has a higher density than the surrounding material. Again no surprise (seismic measurements have measured this long ago) but a nice confirmation, and with a lot of potential for future improvements. -
How does light split into colors?
Today I came home to find very discrete lines of colored light on my living room floor. Can anyone help me to explain this phenomena? I am familiar with dispersion but am wondering how the combination of glass and blinds is creating this effect. When I rotate the shutters as you can see from the pictures, the colors changed... -
Recharge an RV battery by hand cranking a generator
If you've seen breaking bad you probably already know what I'm asking. In this episode I'm watching, they are hand cranking the generator to recharge the battery. They are moving nowhere near as fast as the motor would have spun it. My dad had a hand crank device that was, more or less, a toy. So I'm sure they were producing some electricity... -
How can quarks exist if they are confined?
According to nonperturbative QCD, quarks and gluons don't exist and in nonperturbative QED with two spinors (e.g. proton and electron) hydrogen isn't composed of a proton and an electron. -
Exotic Bicycle Designs and Engineering
Every so often we get requests for engineering projects to work on. One common theme that I've seen is Kickstarter / Indiegogo campaigns for novelty bicycles to solve that last mile problem in urban transportation... -
Gaia parallaxes might reduce tension for Hubble constant
In the last years a discrepancy between two methods to measure the Hubble constant appeared. Measurements based on redshift and the cosmic distance ladder produced results of about 73 km/(s*Mpc) while measurements based on the cosmic microwave background lead to results of about 68 km/(s*Mpc). While not completely outside the uncertainties the difference was still curious... -
Structure of Matter in Quantum Field Theory
This is a topic I've mentioned a few times before. Essentially the structure of matter in quantum gauge field theories is unclear to me. I have no clear question here, just some initial discussion points. So at the first level, it seems a particle based view of quantum field theory is difficult to maintain. In brief on the Hilbert Spaces of interacting field theories there is no well-defined number operator ##N##... -
Soyuz launch failure with crew on board (crew is fine)
A Soyuz flight that was supposed to launch two astronauts to the ISS had a booster failure (half an hour before this post). The Soyuz capsule separated from the rocket and landed, the crew is fine. Rescue teams got to them quickly. While they had to endure higher g-forces than usual they seem to be in a good condition. -
Can anyone learn advanced math?
I often ask myself if anyone can learn math to an advanced level? I think that every healthy person can get very good at math. The only condition is that the person is interested in math. Of course, to get on the level of a Field-Medal winner you have to be blessed a little bit. But I think you can reach and understand a lot just by working out hard. What do you guys think? Can anyone learn math to a high level? -
Black holes squishing Earth
Scares of the CERN accelerator creating a black hole that swallows Earth are in the news once again. I know it is not possible for an accelerator to produce such a black hole in practice. But surely it's impossible even in principle. Surely, a particle accelerator creating a tiny black hole that could grow to swallow the Earth would violate the law of conservation of energy... -
Math Challenge - October 2018
Summer is coming and brings .... Oops, time for a change! Fall (Spring) is here and what's better than to solve some tricky problems on a long dark evening (with the power of returning vitality all around). -
LHCb Discovers Two New Particles
"The LHCb collaboration has found two never-before-seen particles, as well as hints of another new particle, in high-energy proton collisions at the Large Hadron Collider (LHC). Future studies of the properties of these new particles will shed light on the strong force that binds subatomic particles called quarks together." - LHC -
Has the Riemann hypothesis been proven?
I have heard through the grapevine that the Riemann hypothesis has been proven. What I read was this is a claim made by none other than Sir Atiyah himself and that he is planning to give a talk next week. So *if* the statement is true that it is a claim made by Atiyah, then it is of course an extremely serious and probably correct solution... -
Nobel Prize 2018 Announcements
The Nobel Prize winners of 2018 will be announced during the first week of October, starting with the Nobel Prize in Physiology or Medicine on Monday October 1. As most of us are biased towards physics: The physics prize will be announced Tuesday October 2 @ 11.45 (Stockholm time - CEST) at the earliest.
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