(adsbygoogle = window.adsbygoogle || []).push({}); So, long time no see to anyone who remembers me. I had another thread like this, but it's well over 60 days old now so I'm not allowed to bump it.

If you want to know anything about, relativity, quantum mechanics, etc., you can ask me here.

AFAIK there's nothing in current physics that explicitly forbids it. My feeling is that it's not possible because of all of the causality paradoxes that arise. I'm not sure if there's a way around these without invoking extremely speculative approaches, i.e. universe "splitting," etc.

EDIT: I assumed you were talking about time travel to the past. You can certainly "travel" to the future by making use of time dilation from Relativity. Just go away in a spaceship at some significant fraction of the speed of light, then upon returning home you will have aged less than the Earth. For example if you traveled at 99% the speed of light for ~1 year, then turned around and came back at the same speed, you will have aged ~2 years while the Earth will have aged ~14 years.

Or you can hang out near a black hole for a few years, because its large gravitational field will also cause you to age less than the Earth.

I am a little bit stuck on part b of the following problem.


An unusually long-lived unstable atomic state has a lifetime of 1 ms. (a) Roughly what is the minimum uncertainty in its energy? (b) Assuming that the photon emitted when this state decays is visible (lambda =550nm), what are the uncertainty and fractional uncertainty in its wavelength?

For part (a) I solved and got delta E>= hbar/(2*delta_t) -> E=3.29*10^-13 ev

For part (b) I am a little bit unsure of how to go about getting delta_lambda, I tried multiple times but it seems like I end up with another unknown in my equations.


I found an answer key and it says the answers are (a)3.3*10^-13 ev (b) 8*10^-11 nm, 1.5*10^-13


I understand how the 1.5*10^-13 is obtained it is 8*10^-11/550 (assuming the 8 is rounded up and that the actual value is used in the calculation of the fractional uncertainty)

Could you show me how to derive delta_lambda from the uncertainty relations equations? I think it is the delta_t*delta_w >= 1/2 equation and then you can plug in delta_w=2*pi*delta_f but then how do you go from delta_f to delta_lambda, since you can't simply use lambda=c/f.

Thanks!

Do you know any calculus? The uncertainty in wavelength in terms of uncertainty in frequency can be found from the product rule:

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You can find Δf from ΔE=hΔf. When I did it I got 8.051×10^(-11) nm.

What do you use to type the equations?


Also on the topic of time travel if you were traveling near c wouldn't, you technically be able to time travel (only applying to the forward direction).

I used this LaTeX image generator: You must login or register to view this content. . It's mildly inconvenient, because most of the sites I visit these days have LaTeX formatting built in to the forum.



In a sense, yes, this could be considered time travel. See post #11.

Ah I didn't see that you updated your post lol.


For this question

A proton is confined within a one-dimensional box of length a = 22 fm. What energy
is required to excite the proton from the n = 1 state to the n= 3 state?

Do I just use [ATTACH=CONFIG]22347[/ATTACH]


and do it for for both ns and subtract?

I assume we're talking about a box with infinite-potential walls, right? If so, then yes:

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Ok sweet, thanks for the help today!

I'm having a bit of trouble on a physics question I got in my homework last week. Here's the question below, would you be able to PM me the answer. Also if it's not to much trouble could you show all your workings.