# Search results

1. ### I Symmetry associated with current conservation

Dale - Thanks - that's very helpful. You write: " The Noether current and the Noether charge are related through a continuity equation which essentially defines a local conservation law. " What is the continuity equation? Where does the J I see so often come in? Aclaret's post as is is a...
2. ### I Symmetry associated with current conservation

As I understand it for every symmetry there is associated a conserved quantity - so for time symmetry there is energy conservation. I understand as well that charge conservation is associated with a 'mathematical' local symmetry - something turning in a mathematical space at a point so to...
3. ### I Poynting vector - uniform vs accelerated charge

I am trying to understand why an accelerating charge emits radiation/electromagnetic waves but a uniformly moving one does not. I saw one video on Youtube where it seemed that it was explained by the fact that with a uniformly moving charge the Poynting vector was pointing 'in to the volume' -...
4. ### I Duration of electromagnetic disturbance

Choosing to end this for now. Not getting very far. I will have to think about how to re-ask. Thanks for trying.
5. ### I Duration of electromagnetic disturbance

Nugatory/Davenn Thanks for the clarification. Those are the kinds of answers I was expecting to get and most always have gotten on PF. The articles I read prior to posting - many of them - did not make the critical distinction between accelerating and non-accelerating charges - you can see...
6. ### I Duration of electromagnetic disturbance

Google: +++++++++++++++++++ https://www.google.com/search?q=moving+charges+electromagnetism&oq=moving+charges+electromagnetism&aqs=chrome..69i57.10416j0j7&sourceid=chrome&ie=UTF-8 "Electromagnetic radiation, is a form of energy emitted bymoving charged particles. " "When a charged...
7. ### I Duration of electromagnetic disturbance

Let us say I have a moving charge. At each point x,y,z in it's path from understanding there is a transverse electromagnetic wave being radiated (could also be viewed as a photon). The electric field at any point x1,y1,z1 in the path is disturbed. The moving charge does the same thing all...
8. ### B Changing electric field generating magnetic field

Thanks for the quick and definitive response. This point was not made clear in a lot of material I saw - it always had reversal of direction - so negative and positive charges swapping repeatedly. That being said what difference does that particular scenario make as to the simply...
9. ### B Changing electric field generating magnetic field

I would very much appreciate a clarification on what is meant by a changing electric field in the context of statements such as 'a changing electric field creates a changing magnetic field'. My question is does the electric field actually need to reverse as a lot of examples show where two...
10. ### I Do electromagnetic waves have potential and kinetic energy

sophiecentaur: Thanks for quick reply. However I do not know what E and H are that you refer to? CWatters: Thanks for the link but I see nothing in there about potential and kinetic energy of an electromagnetic wave. I saw a video about a string wave on Youtube and with the string I understood...
11. ### I Do electromagnetic waves have potential and kinetic energy

Do electromagnetic waves have potential and kinetic energy like springs, strings, etc. If so how are they calculated, inter-related? What is the total energy? Are the energies fluctuating over time? I am a physics hobbyist so generally the first answers should come with the least mathematics...
12. ### I Gauge Symmetry

Thanks for the distinction between gauge symmetry and gauge invariance. I think however based on the amount that I see gauge symmetry used it will be a long battle to knock it out of use. Or is there such a thing as gauge symmetry apart from gauge invariance?
13. ### I Angular sector

Thanks. So what is the formula for calculating A using the parameters referenced? A picture or illustration would be great so I can see what exactly the variables refer to.
14. ### I Angular sector

In this article https://terrytao.files.wordpress.com/2008/03/ricci1.pdf the following is written: "Consider now an angular sector A(x, r, θ, v) inside a small disk B(x, r) of small angular aperture θ (measured in radians) centred around some direction v (a unit vector) emanating from x; this...
15. ### I Gauge Symmetry

I have reviewed the various posts on gauge symmetry in particular this one which is now closed. In this post there is the following link:http://www.vttoth.com/CMS/physics-notes/124-the-principle-of-gauge-invariance. This is a good read. However, there is some clarification I need. The...
16. ### I Information for black hole region in surface surrounding it

Thanks. However I would like more detail/less analogy. The question is straightforward - might be completely nonsensical to someone in the field or not answerable currently - I will take either. So in summary 3000 bits of information in black hole - surface confirms the total number of bits...
17. ### I Quantum bits information lost in black holes

I think everybody is trying to provide to help but unfortunately I am not getting much out of this thread - lost me at unicorn for sure. There's far to much of that kind of diversion in social media chats. It seems to be built into the DNA of social media. I have no cure for it - I think like...
18. ### I Black hole - between horizon and singularity

We can't see into a black hole. Whatever is in the black hole can't see us. That part seems to be clear to me. However as the surface of a black hole is conjectured to have all the bits in the black hole - in fact is the limit of the bits in the black hole - it seems there is something in the...
19. ### I Black hole - event horizon and Hawking radiation

Thanks for the response. As far as my question - "Are the analogy-style answers not even possible? In other words pair-production taking place just outside of the event horizon doesn't play any role at all? It happens but so what as far as radiation/evaporation of black holes - "so what "...
20. ### I Spacetime moving faster than speed of light?

Thanks for all the feedback and the distinction between traveling and recession/expansion. I dug this up - https://www.universetoday.com/119068/how-can-space-travel-faster-than-the-speed-of-light/ It seems to put some flesh on the barebones statement of something moving faster than the speed...
21. ### I Spacetime moving faster than speed of light?

I was watching a seminar on black holes and one of the participants threw out as an aside that spacetime could travel faster than the speed of light - so within spacetime nothing could travel faster than spacetime but spacetime itself however was not bound by this rule so it could move faster...
22. ### I Information for black hole region in surface surrounding it

At one point I read there was the concern that a black hole could lose bits of information. Then a theory arose that showed that all the bits in a black hole were to be found on the surface of the black hole. Thus if there were let's say 1000 particles in a black hole each of which could be...
23. ### I Black hole - event horizon and Hawking radiation

I have come across the following multi-explanations of how Hawking radiation/evaporation of a black hole happens: Particle/anti-particle story: particle/antiparticle pair creation from vacuum near the event get torn apart - one going into black hole, the other away; in some of these...
24. ### I Black hole - between horizon and singularity

What occupies the space between a black hole's event horizon and the singularity? Stuff hurtling to the singularity? Vacuum?
25. ### I Black hole radiation

I have done a forum search - did not clarify. I am not sure why your first assumption is that I haven't. +++++++ As far as: "Technically yes, but you're overthinking it. As you pass from say a few miles outside the EH of a supermassive BH to a few miles inside, you'll observer practically no...
26. ### I Black hole radiation

A couple of points I need clarification on. Objects outside of the event horizon feel the pull of the black hole - so the closer the object is to the event horizon but still outside of it the more pull the object feels to be sucked into the event horizon? Is that the correct view? As far...
27. ### I Quantum bits information lost in black holes

Thanks. When I use the word 'information' I am just using the word I read so it's not what I mean by it, it's what's meant when people use the word in the context I described. I am asking for the meaning of information as in the common phrase in this area - 'information' is lost in the black hole'.
28. ### I Quantum bits information lost in black holes

I have just started googling/youtubeing black holes. One point made repeatedly discussed is the loss of information in black holes. In particular quantum bits. What I have not yet found is very much explanation of what these potentially lost bits might be. So what I would like to know is...
29. ### B Weak nuclear force - circumstances in which it is manifested

Thanks for the quick response. If tritium is present then somehow there ends up being unbound neutrons which decay into protons? I am asking because per this wiki note - https://en.wikipedia.org/wiki/Weak_interaction - "A particularly extreme example is the weak-force decay of a free neutron...
30. ### B Weak nuclear force - circumstances in which it is manifested

I have a glass of water at room temperature. The electromagnetic force is at play between the electrons and nucleus of the atoms, the strong nuclear force is at play holding the nucleus together, the force of gravity weak as it may be is at play between the various particles - electrons, quarks...