The h Bar

Washington A. Ramos

3:33 AM

Hey, I believe there's a typo in an answer but I can't edit since it's too little characters

In the accepted answer here: physics.stackexchange.com/questions/259302/…

Second paragraph: "equally often, poorly explained meme."

I believe he meant "theme"?

ACuriousMind

7:17 AM

@WashingtonA.Ramos no, I think the author is calling the idea that "time is an added fourth dimension" a meme, i. E. an almost virally spread idea. I find the answer a bit weird but I don't think it's a typo

Secret

8:17 AM

Why we can assume scattering can be modelled by an S-matrix, that is a linear operator. Is it always possible for a matrix to include all nonlinearities in its components?

Is this linearity even in quantum field theory possible because the quantum states in the infinite past and future are somehow have components that are mutually orthogonal, and hence linearity holds?

Physics Meta

8:36 AM

-6

Q: Why is the physics stack exchange such a piece of shit?

If you're apart of the Math Stack Exchange, its such an involved and respectful community. They assist with homework, people ask arbitrary and deep questions. There are great discussions and connections. Not to mention the amount of activity on it, there is no one the PSE and that's weird. Here,...

Scientist Smith YT

@JakeRose Yep. But it shouldn't come to any suprise though. These yokes with current PMTC Permanent Magnet Technology Capabilities can get up to 35 Tesla. Also, FYI MRI machines are 1 - 6 Tesla. Specially made scientific MRI machines are 12.5 - 21 Tesla. MRI machines can't get above 21.1 Tesla with today's technology capabilities. Maybe in a year or so we can gain that technology capability.

@JakeRose Worlds most powerful constant on electromagnet is the 45 Tesla Hybrid down in Tallahassee Florida at the National Magnet Laboratory. Or in short MagLab. They also host the world most powerful pulsed electromagnet. At 100 Tesla this electromagnet is a pure monster. It is under tens of thousands of PSI. I believe... If I remember correctly, the 45 Tesla Hybrid coils are under 12,000 PSI of electromagnetic force.

@JakeRose A lot can be learned if you go their. I've been there quite a few times and I love seeing the raw generators and capacitors used on the 100 Tesla multishot electromagnet. But I personally think the 45 Tesla Hybrid is a beauty and a work of art. But the 100 Tesla magnet is also impressive. It's hard to decide.

Scientist Smith YT

8:59 AM

Even though these can make powerful magnetic fields, don't be fooled by it's size. Making these yokes are very very VERY dangerous. Making a yoke is recommended for those that have at least 10 years or more of experience with magnetics. Personally, I don't recommend anyone that isn't thoroughly trained and experienced to make a PMY Permanent Magnet Yoke. Neodymium magnets of 2 by 2 inch grade N52 size aren't toys.

Attracting Snaping Distance: 12.5 - 14 inches, pull strength: 400 pounds * speed = impact force. Speed can easily reach up to 20 MPH. Sheer force is pulling strength divided by 2. Ex. 400 pounds / 2 = 200 pounds of sheer force.

Emilio Pisanty

9:18 AM

-1

Q: What is Neodymium?

What is Neodymium? I'm not quite sure why i was redirected here. I was curious about magnets. I wondered how magnetizing a drill bit worked. I originally wanted to know how long the magnetization would last. Google gave a 3 part response. The temporary magnetization, the Neodymium, which would lo...

electromagnetism atomic-physics elements

Any thoughts on removing the second half of that question, to keep it on topic?

Loong

With the link to Wikipedia that was introduced in an edit, the question now also contains the answer.

Emilio Pisanty

@Loong I mean, yes, also that

But the second half of the post is just a rant with nothing to do with neodymium

Korra

10:08 AM

Sorry for this, but can someone look at my question?

0

Q: Annihilation of virtual particles

Consider this scenario. We have two virtual particles form in a point in space. Let us consider them to be electron-positron pair. Now suppose an ELectron (not virtual) comes near the positron, nearer to the positron than the virtual electron which was the part of the virtual particles pair. If s...

conservation-laws coulombs-law virtual-particles

tpg2114

10:45 AM

Bummer... my 2x500 rep bounties didn't attract any new answers :(

Korra

11:54 AM

@tpg2114 can you link that here? I want to see it.

Emilio Pisanty

12:32 PM

@Korra physics.stackexchange.com/users/6634/tpg2114?tab=bounties

> You've asked two questions. One was answered, one is about the most "disrespectful" thing I've seen on SE for years.

damn

now I'm really curious

Physics Meta

1

Q: How to flag an anonymous suggested edit?

I'm new to the "Suggested Edits" review queue. Recently, I was asked to review an edit suggested by an anonymous user which if accepted would actively harm our site. I rejected the edit. Is there any way to flag an edit by an anonymous user in order to prevent such circumstances in future? I did...

support editing flagging suggested-edits

JMac

@EmilioPisanty Tools > Recently Deleted. Top of the pile, should be pretty obvious which one it is :P

Wait that's the same one

IDK if that's what he meant or not.

It was originally in the regular site though, so possibly.

Emilio Pisanty

12:50 PM

@JMac ah, I hadn't noticed that

John Rennie

Ah yes :-)

ZeroTheHero

1:36 PM

@JMac wow...

This guy has a chip on his shoulder...

JMac

1:57 PM

@ZeroTheHero It's strange how upset some people get that a site doesn't work like they want. Someone explained it really well on meta. It's like every other online community, where before you try to actively participate, you need to take some time to get a feel for the site and the community. I don't know why people expect to successfully jump into existing communities and change them to be what they were looking for.

Korra

2:15 PM

I am doing this again, (｡•́︿•̀｡)

1

Q: Tunneling in quantum mechanics

We have this well known case of ~4.2 MeV α-particle being emitted from the U-238 nucleus but the α-particle emitted from the Po-212 which has the energy of ~9MeV cannot penetrate it. This phenomenon is explained by the tunneling effect from quantum mechanics. Now, of the tunneling can happen f...

quantum-mechanics nuclear-physics quantum-tunneling

JMac

So reading this question I was thinking, could you say your event horizon is technically the distance where the gravitational force is exactly zero? I don't think it would be useful as an answer to that question; but it just had me curious about that. I know basically nothing about relativity so I don't know how wrong such a statement would be.

But as far as I understand gravity can't act from beyond the event horizion.

Javier

@JMac I don't think it makes sense to say that. The apparently simple concept of gravitational force is not easy to define in GR, but it certainly wouldn't be zero at the EH

JMac

2:31 PM

@Javier I thought information about gravitational fields couldn't travel faster than the speed of light.

Javier

That's right, but what does that have to do with the force being zero?

JMac

@Javier If the force from it were non-zero, wouldn't that be information about the gravitational field travelling faster than light?

Well the equivalent of Newtonian gravitational force I guess you would say (which is why it doesn't make sense to talk about in that question)

Javier

@J

@JMac you can read some of the answers at physics.stackexchange.com/questions/937/…

IMO the bottom line is that the crucial point is that the grav field of a black hole is static. The information was already there when the black hole formed, because the mass from which it formed had its own gravitational field

No information has to travel

JMac

@Javier hahaha whoops I'm an idiot. I meant to say the edge of the observable universe, not the event horizon. I do somewhat understand why that doesn't work with EH's, and that's definitely not what I was thinking.

Javier

@JMac oh I get what you meant now

JMac

2:40 PM

It probably helps when I actually say what I mean lmao

Javier

I guess in a sense that's true then, if you trace the history of the BH's mass back to the big bang, it has a maximum sphere of influence

lol

Javier

3:31 PM

Take the Reissner-Nordström metric, $ds^2 = -f(r)dt^2 + dr^2/f(r) + r^2 d\Omega^2$, with $f(r) = 1 - 2M/r + Q^2/r^2$. Let's say we replace the charge term by something with an arbitrary power of r, $f(r) = 1 - 2M/r + A/r^b$. Does this metric have a standard name? It shows up a bunch in alternatives to GR and for some matter contents, but everyone seems to have their own name for it.

Washington A. Ramos

4:13 PM

@ACuriousMind I see. I'm a programmer, not a physicist, was just being curious around Physics SE and I found it weird to see internet jargons in a StackExchange site.

Transcript for