The h Bar

2:11 AM

Ah, nice. "I read the answers and I don't like them. Won't someone tell me the answer I want instead of the correct one?" ::sigh::

On another front the wife was just complaining about an unidentified smell.

Turns out is was coming from the copy of Harry Potter and the Second-Hand Smoke that she checked out of the library.

Bernard Meurer

Harry Potter and the Second-Hand Smoke?

What the hell kind of story is that?

dmckee

A library book that reeks and induces coughing.

user507974

2:49 AM

@dmckee Cuban import clearly

$sigh$ man, kinetics can take a long time

lvella

4:42 AM

some physicist please talk to me

user116211

@lvella Is there any problem?

lvella

if I have two 1 Kg mass iron balls floating in space, one touching another

user116211

You can post your query here.... any willing one would respond. BTW, this is a off-time; to get everyone, better come 3-4hrs later.

lvella

the system mass is 2 Kg, i take

but if those balls are very far apart, say, 100,000 ly, the system mass for the two balls is still 2 Kg?

or does the potential gravitational energy between the two of them increases the system mass according to E=mc² ?

John Rennie

6:04 AM

@lvella if the two balls weigh 2kg when they are touching they will weight slightly more when they have been separated.

This seems odd at first, but look at it this way:
To separate balls you have to do work on the system and that means you are increasing its internal energy. If you increase its internal energy by some amount E then the mass increases by E/c^2.

For example a hydrogen atom weighs slightly less than a separated proton and electron. In fact it weighs 13.6eV less, where that figure of 13.6eV is the ionisation energy of the hydrogen atom.

user507974

6:27 AM

@JohnRennie the second i read that i knew where it was going

user116211

7:52 AM

@yuggib: o/

Slereah

8:12 AM

hey

FrancescoS

hey

Slereah

Is there an equivalent of time ordering for non-relativistic path integrals?

I don't recall ever seeing it

Slereah

8:50 AM

Oh wait

I found the axiom that defines a time orientation for Wightman

"The generators $(H = P_0,\vec P)$ of the translation subgroup have spectrum in the forward lightcone $p_0 - \vec p^2 \geq 0$, $p_0 \geq 0$."

Secret

9:11 AM

Strange question" In order for a given state $\lvert \psi \rangle$ to change, must an interaction necessary to bring upon the change, or it can do spontaneously?

I noticed that since the hamitonian is a generator of time translation, and that "waiting" as outlined in feymanns lecture note can be considered as an operator. Does that mean time also count as an interaction, or is it a separate thing?

Slereah

A state can change with time, yes

Using the propagator you can find that change

Secret

@slereah so is time considered an interaction to the state in this context. If not, how is it differ from an interaction given that both a state changes with time and a state changed because of interacting with something can be described by the hamiltonian?

Slereah

$\psi(x_2) = \int K(x_1, x_2) \psi(x_1) dx_1$

No

Secret

9:26 AM

Put the question in another way, why is the propagator not an interaction term to the state given that both propagators and interaction terms can change the state?

Slereah

It just describes how the wavefunction evolves

I mean would you call a free particle moving in the vacuum an interaction

it moves but doesn't interact

Secret

Hmm... make sense

Wrzlprmft

9:48 AM

I could answer this question which looks like a homework question (the asker is completely off-track). As there is not much of a guideline for this: Should I rather give tips, only tell the asker where they are wrong or something else?

user116211

@Wrzlprmft Answering in comment is definitely not right since we are not a forum but yeh, you can give some minor hints... presently the question is off-topic, I deem.

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