# immijimmi

Senior Members

35

## Profile Information

• Favorite Area of Science
Quantum Physics

3

1. ## Stress-energy Tensors for Dummies

I'd like to learn about this, but the wiki page is incomprehensible to me. From my understanding, this explains how energy can exert a gravitational pull (along with a lot of other factors). Can someone explain how that works to me? I'm currently learning AS physics so I don't have much of an understanding of any complex ideas... keeping that in mind please don't overcomplicate it, or introduce any theories I won't understand without explanation. Thanks in advance!
2. ## Why can't you isolate a quark?

My apologies, I mistook attributes of the residual strong force as effective on both types. I have an interesting thought experiment related to this topic, however: In the event that tachyons exist, would a tachyonic quark be able bind with bradyonic quarks into a composite particle if it was to orbit the other quarks at superluminal speeds?
3. ## Weak Interaction Questions

Maybe I should wait until I understand particle physics more before I attempt to venture into this particular topic...
4. ## Having 0 kinetic energy

...What? The reason we see things which photons have bounced off is that the photons that are not absorbed are of a specific frequency or frequencies, which gives us the colour of the object. Put all the photons that enter your eyes together and you get an image. The photons that reached us don't carry an image of the incident. They won't have changed at all. We can't measure anything from this lone photon you're talking about unless we know some other details of the incident. (for example, we could measure when it happened if we knew where, by calculating distance/speed).
5. ## Having 0 kinetic energy

I was gonna put a post here about how it's impossible to measure a 0 in motion because it would mean inertia compared to everything else, and that we should be focusing on a zero in temperature. However something just ocurred to me: physicists used to think that motion was relative to the universe itself, right? Well, we know that light is always moving at c. To maintain this constant speed it cant really be moving relatively to anything, can it? We also think that it appears to move slower at times to to gravity, etc. curving spacetime around it. We've applied this to how black holes absorb light. If it appears to slow down when crossing an area containing a different 'density' of spacetime, then it's moving relative to that. In light of this, why aren't we measuring motion relative to the fabric of spacetime? that would mean that you have to take into account movement compared to this substance (if it can be called a substance) as well as temperature, if you want to stop an object's time. Or you could just flood the area with gravitons.
6. ## What separates particles and antiparticles?

Found it!! It isnt helicity because they don't travel at c so it's technically a variable. Apparently it's chirality. I had to look in the wiki page for sterile neutrinos to find that gem, though. Credit to DrRocket for the original suggestion of chirality though.
7. ## Weak Interaction Questions

This sounds dense of me, but is there any way you could explain that to an AS physics student? I dont know what the 'weak-mixing angle' or 'orthogonal' mean, and i'm not sure what the intended meaning of 'eigenstates' is in that context. If something has an eigenstate that means that you know the exact values of its quantum numbers. How do you apply that to a force? (I'm quite new to eigenstates too actually so correct me if that last was wrong)
8. ## Some questions on strong interaction

Ok, but that still leaves six other observed states and not 8. And, if r /r = colorless, which it does, why do I have to involve b /b and g /g? (as an example) How is gluon fission relevant to whether quarks have color charge at creation? I mean, sure, you're showing how quarks with c-charge can be created from a gluon, but that already has color charge to pass on. I'm pretty sure that quarks have color charge from creation, but I wasn't sure.
9. ## Why can't you isolate a quark?

From the Wiki page: The strong interaction is observable in two areas: on a larger scale (about 1 to 3 femtometers (fm)), it is the force that binds protons and neutrons together to form the nucleus of an atom. On the smaller scale (less than about 0.8 fm, the radius of a nucleon), it is also the force (carried by gluons) that holds quarks together to form protons, neutrons and other hadron particles. Strong interaction isn't observed after 3fm, like I said, so we don't know from this information if it has any effect past this distance. I know i've read somewhere that gluons have mass and was .14 MeV. Regardless of whether they do or not, there is actually another explanation for the limited range of the color force: http://en.wikipedia.org/wiki/Gluon Scroll down to 'confinement' and read.
10. ## is everything just photons

Everything is made of energy. When things release photons it is because photons are made of energy and not much else, therefore they are easy to create as an outlet for spare energy. One reason photons can't be the fundamental constituents of matter would be that they don't have color charge, electric charge or mass, and most components of matter possess these qualities.
11. ## Why does matter behave like particles when observed, and like waves when not?

I dont get why everyone separates these behaviors. As I see it, all matter behaves as wavicles. They can exhibit both properties at once, and the nature of observation determines which behavior we see.
12. ## Having 0 kinetic energy

about 288K? When he refers to kinetic energy having an effect on time it isnt necessarily net movement. The rock is vibrating in your hand but not to a noticeable degree. Temperature is to movement what distance is to displacement, I suppose. If I kick a ball 5m into the air and it lands where i kicked it from, distance travelled is 10m but displacement is 0m. If you hold a rock steady in your hand, its movement is 0 but its temperature (and therefore kinetic energy) is quite a bit more.
13. ## Weak Interaction Questions

1. Weak interaction is the only method by which strangeness and CP can be violated. What's so special about it that it can do this? 2. The only gauge bosons that have mass are both associated with this force. Is that significant?
14. ## Particle spin

But the wiki for spin in particle physics says: 'Spin is a type of angular momentum, where angular momentum is defined in the modern way as the "generator of rotations" I'm confused... >.<
15. ## Some questions on strong interaction

So, the gluon singlet state is a 'colourless' gluon? There are 3 of those, though... that means there are only 6 combinations: r /b r /g b /r b /g g /r g /b The three that wouldn't be observed are: r /r b /b g /g So, why are there 8 observed?
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