David H
Reputation
1,262
Next privilege 2,000 Rep.
 Feb 20 comment Why do electrons and protons attract each other? First, go watch the YouTube video Feynman, magnets, and why questions. Feb 19 comment where does the photon go after scattering? Another process where mass is conversed is the electrolysis of water, i.e. the conversion of water into oxygen and hydrogen: $2\text{H}_2\text{O}\rightarrow2\text{H}_2+\text{O}_2$. The mass before and after the reaction is conserved, but the number of molecules is not. It makes no sense to ask "where did the H2O molecules go?" because after the reaction, the H2O molecules aren't anywhere. They're simply gone. In much the same way, photon number isn't conserved either. I apologize for the lengthy comments. Hopefully they'll still be helpful. Feb 19 comment where does the photon go after scattering? The law of conservation of mass tells us that the amount of mass of a closed system is constant; mass can neither be created nor destroyed. Suppose you weigh a pot of water before and after boiling it for some time. You'll notice that it weighs less afterwards. From the law of conservation of mass, you can infer that since the mass of the missing water couldn't have simply been destroyed, and that the missing mass will be found if we look in the right place (collect and weight the water vapor). (2/3) Feb 19 comment where does the photon go after scattering? Where does the flame go after you blow out a candle? Where does the sound of someone's voice go after it has reached your ears? When something disappears in one location, you have to think carefully about whether or not it's reasonable to infer that it must have gone somewhere else (as opposed to being gone altogether). The intuition that "all things must be somewhere, so if it's not here then it must be somewhere else" is justified by the various physical conservation laws (mass, energy, momentum, charge, etc.) and spatiotemporal continuity. (1/2) Feb 3 comment How come the universe is made of matter and not antimatter? @SajinShereef See Brandon's comment above. At the moment, you aren't really asking a question worth answering. Asking why antimatter lost the tug-o-war is like asking why the team with the least points lost. "Ordinary matter" is a label we slap in the winner, and anti-matter is a label we slap on its opposite. A better question is why is there a winner at all? Feb 3 comment How come the universe is made of matter and not antimatter? @WetSavannaAnimalakaRodVance Hehe, for a moment there I thought you were talking about Mike Brown the planetary scientist. I took a freshman intro geology class he taught, and I was about to be very confused how a theoretical physicist with a dissertation in frontier theoretical QFT topics transitioned into the guy who taught me how to recognize feldspar. =D Feb 3 comment What is the future of our universe? The ultimate fate of the Universe is a major open question in cosmology. That means physicists are trying to figure this out as we speak, and whoever does figure it out will most likely win a trip to Stockholm. It is unlikely that such a Nobel Prize winning solution will make its debut published as a response on these forums. Jan 27 comment What is an Electron? @Ciwan What you really must accept is that we'll never understand the most fundamental stuff we know of in terms of more fundamental stuff. Even if we discovered that electrons are not fundamental and they're actually made up of tiny little electrinos, you'd just be back in the same boat asking me what the heck are electrinos. Jan 27 comment Application of $E = mc^2$ What do you mean be "pure energy state"? Jan 26 comment Motion of objects (beginner) Yes, though I'd recommend being more specific: the motion is uniformly rectilinear. Jan 26 comment Motion of objects (beginner) The curves traced out by the reflectors do not have semi-circlular parts. The curve is called a cycloid. en.wikipedia.org/wiki/Cycloid Jan 22 comment Because position is relative, is it possible to see a star orbiting a planet? The Sun is orbiting Saturn as we speak. Jan 21 comment Reunion condition in the Twin Paradox The condition for reunion is that both twins have the same spacetime coordinates. This is true whether you are talking about Newtonian physics or relativistic physics. Jan 18 revised Is the concept of a field necessary to electrodynamics? fixed grammars Jan 18 answered Is the concept of a field necessary to electrodynamics? Jan 17 comment Why aren't quarks free? Your first question is maybe one of the top ten unsolved problems in physics at the moment. No one knows yet. Some physicists are hopeful that string theory will solve answer this question, assuming we ever figure out how to test string theory. Jan 16 answered Capacitance and energy Jan 16 comment Axis of reflection in a mirror Richard Feynman explains it best, as usual. youtube.com/watch?v=msN87y-iEx0 Jan 16 comment Should I learn Classical Physics if I want to learn Quantum Physics? A better question is CAN you learn quantum physics without learning classical physics? Jan 15 comment A basic question: what is accelerating voltage? Context? Also, is this what you're referring to? en.wikipedia.org/wiki/Acceleration_voltage