Strange Posted March 18, 2018 Posted March 18, 2018 (edited) To be fair, natural units are a thing. But I can't see how that it is at all relevant. Captcass seems to be complaining that he used natural units when he shouldn't have. And we didn't spot it. Or something. (In natural units it would just reduce to "l * E = 1/2".) The OP claimed that "length and energy are related: l * E = ħ / 2". The units wouldn't make any difference to the truth or otherwise of this statement. And it still looks bogus to me (it is not dimensionally consistent, apart from anything else). On 3/1/2018 at 7:36 PM, captcass said: Heisenberg's uncertainty principle tells us that ... Expand \sigma_{x}\sigma_{p} \geq \frac{\hbar}{2} For position and momentum. Length and energy are not related in this way. Edited March 18, 2018 by Strange
koti Posted March 18, 2018 Posted March 18, 2018 On 3/18/2018 at 9:53 PM, Strange said: To be fair, natural units are a thing. But I can't see how that it is at all relevant. Captcass seems to be complaining that he used natural units when he shouldn't have. And we didn't spot it. Or something. (In natural units it would just reduce to "l * E = 1/2".) The OP claimed that "length and energy are related: l * E = ħ / 2". The units wouldn't make any difference to the truth or otherwise of this statement. And it still looks bogus to me (it is not dimensionally consistent, apart from anything else). Expand Why would anyone use natural units for c and hbar and then convert back? I don’t understand...might as well use the units I proposed above if we are to convert back anyway.
Strange Posted March 18, 2018 Posted March 18, 2018 On 3/18/2018 at 10:10 PM, koti said: Why would anyone use natural units for c and hbar and then convert back? Expand Fair point.
captcass Posted March 18, 2018 Author Posted March 18, 2018 On 3/18/2018 at 10:10 PM, koti said: Why would anyone use natural units for c and hbar and then convert back? Expand Apparently I have been way overestimating you folk. Natural units are used to simplify calculations by dropping out terms by making them = 1. It eliminates a lot of infinities and Pi factors from the calculations. When the final result is achieved, to find the actual result, you factor those elements back in. In particle physics they make h-bar and c = 1. https://en.wikipedia.org/wiki/Natural_units http://www.phys.ufl.edu/~avery/course/4390/f2015/lectures/natural_units.pdf
swansont Posted March 18, 2018 Posted March 18, 2018 On 3/18/2018 at 8:58 PM, captcass said: This was in my original question. Without re-reading it all, I don't believe anyone noticed (as I didn't when I posted it, duh) that it is in "natural units". To find the answer in the correct units, the c and h-bar elements have to added back in. I think this would have been the correct reply to my question. Expand Oh, it was noticed. But since it's wrong, it doesn't matter. How about showing your work? Derive the expression.
Strange Posted March 18, 2018 Posted March 18, 2018 On 3/18/2018 at 10:43 PM, captcass said: Natural units are used to simplify calculations by dropping out terms by making them = 1. It eliminates a lot of infinities and Pi factors from the calculations. When the final result is achieved, to find the actual result, you factor those elements back in. In particle physics they make h-bar and c = 1. Expand If you really think all that complexity is necessary when multiplying two numbers, I feel sorry for you ...
koti Posted March 18, 2018 Posted March 18, 2018 On 3/18/2018 at 11:18 PM, Strange said: If you really think all that complexity is necessary when multiplying two numbers, I feel sorry for you ... Expand Abacus comes to mind.
captcass Posted March 19, 2018 Author Posted March 19, 2018 On 3/18/2018 at 9:53 PM, Strange said: To be fair, natural units are a thing. But I can't see how that it is at all relevant. Captcass seems to be complaining that he used natural units when he shouldn't have Expand It is relevant because I was asking about the relationship of energy and length when I found the relationship in a particle physics book. The proper answer is that there is no recognized relationship between length and energy. The relationship is only used when doing computations using natural units...... That's it for me here. BiBi
Strange Posted March 19, 2018 Posted March 19, 2018 On 3/19/2018 at 12:40 AM, captcass said: The proper answer is that there is no recognized relationship between length and energy. The relationship is only used when doing computations using natural units...... Expand If there is no relationship why would it be used? It doesn’t make any sense.
swansont Posted March 19, 2018 Posted March 19, 2018 On 3/19/2018 at 12:40 AM, captcass said: It is relevant because I was asking about the relationship of energy and length when I found the relationship in a particle physics book. The proper answer is that there is no recognized relationship between length and energy. The relationship is only used when doing computations using natural units...... That's it for me here. BiBi Expand BS Natural units don't let you arbitrarily put the constants back in. You might use E = m for convenience, but you can't then arbitrarily plug an hbar into the equation and claim there is meaning to it. If you "found" a relationship in a particle physics book I'm guessing there was context to it that you are not including (like it was a scaling factor, rather than equality)
captcass Posted March 19, 2018 Author Posted March 19, 2018 On 3/19/2018 at 9:58 AM, swansont said: Natural units don't let you arbitrarily put the constants back in. Expand I didn't say that. BiBi
swansont Posted March 19, 2018 Posted March 19, 2018 On 3/19/2018 at 2:56 PM, captcass said: I didn't say that. BiBi Expand Then show your work, as I've already asked.
captcass Posted March 19, 2018 Author Posted March 19, 2018 On 3/19/2018 at 3:22 PM, swansont said: Then show your work, as I've already asked. Expand Lol. I have no idea what you are asking for here. I started this thread with a simple question asking for clarification. I did this because, even though it was right in front of me, I missed that it was in natural units. There is no math here. There is no derivation. I am not making any claims here. I just wanted your folks' help in clarifying, which no one really did. Strange came closest when he said, " Note that this refers to wavelength, not length in general. But your question still applies. " So......there are no bones to pick here. Thanks. BiBi
Strange Posted March 19, 2018 Posted March 19, 2018 (edited) On 3/19/2018 at 3:55 PM, captcass said: I am not making any claims here. Expand You claimed that "length and energy are related: l * E = ħ / 2" This is obviously wrong. And has nothing to do with the uncertainty principle. On 3/19/2018 at 3:55 PM, captcass said: I missed that it was in natural units Expand You still haven't explained how that is relevant. Your claim is wrong in any units. On 3/19/2018 at 3:55 PM, captcass said: There is no math here. There is no derivation. Expand And that is the problem. You are posting unsubstantiated nonsense. On 3/19/2018 at 3:55 PM, captcass said: Strange came closest when he said, " Note that this refers to wavelength, not length in general. Expand There is a relationship between energy and wavelength, but it is not the one you claim. Edited March 19, 2018 by Strange
captcass Posted March 19, 2018 Author Posted March 19, 2018 On 3/19/2018 at 4:06 PM, Strange said: You claimed that "length and energy are related: Expand lol. I did not claim this. I asked you folks for clarification about what I found in the particle physics book, that is all. On 3/19/2018 at 4:06 PM, Strange said: There is a relationship between energy and wavelength, but it is not the one you claim. Expand I am NOT claiming anything! I understand the relationship between energy and wavelength! My question had nothing to do with that aspect. It was based on my own misunderstanding on what I read. This thread is dead and I am moving on. Thanks for your time......
swansont Posted March 19, 2018 Posted March 19, 2018 On 3/19/2018 at 4:13 PM, captcass said: lol. I did not claim this. Expand "Heisenberg's uncertainty principle tells us that length and energy are related: l * E = ħ / 2 and using natural units where c = 1= ħ, we can deduce that 2*10-16 m = 1 / GeV." This is literally the first sentence of your OP. (emphasis added) If you can't derive it, or have no math to show, then where did you read it?
captcass Posted March 19, 2018 Author Posted March 19, 2018 On 3/19/2018 at 4:43 PM, swansont said: This is literally the first sentence of your OP. Expand That is literally what I found in the book and asked you folks for clarification on. Hello? I will not be responding to any more of these..... I provided the link to the book early on. I haven't the time for this......IT WAS A MISUNDERSTANDING ON MY PART TO BEGIN WITH!. Geeze! OK. Here it is again: https://books.google.com/books?id=SW3FCwAAQBAJ&pg=PA49&lpg=PA49&dq=1.782662×10−36+kg&source=bl&ots=17y_BtXxUY&sig=DCfJ6RQ8drGjYwW8zGOxQsgDjt8&hl=en&sa=X&ved=0ahUKEwjV47qBsMnZAhUS9WMKHd0mATwQ6AEIPTAC#v=onepage&q=1.782662×10−36 kg&f=false Here is a link to the book. The applicable section is on page #49 Have fun with it. I now understand it so I am done with it....... BiBi
swansont Posted March 19, 2018 Posted March 19, 2018 On 3/19/2018 at 5:59 PM, captcass said: That is literally what I found in the book and asked you folks for clarification on. Hello? Expand I missed that. But I see what is going on. The author is in error. It has nothing to do with the HUP. If you set hbar*c = 1, you get the relationship that 1m equates to 2 x 10^16 / GeV (3 x 10^8m/s) * (4.15 x 10^-15 eV-s/2π) = 2 x 10^-7 eV-m It is simply a byproduct of natural units.
captcass Posted March 19, 2018 Author Posted March 19, 2018 On 3/19/2018 at 6:20 PM, swansont said: It is simply a byproduct of natural units. Expand Thank You! That is what I have been saying. I didn't see that before I asked the question. The author does not show how he derives it from HUP, but I took him at his word, as odd as it also seemed to me..... OK. Now I think the thread is done....yes? Thanks for your time, folks.
swansont Posted March 20, 2018 Posted March 20, 2018 On 3/19/2018 at 7:35 PM, captcass said: Thank You! That is what I have been saying. I didn't see that before I asked the question. Expand It's not something that has physical meaning, though. It's simply a conversion factor. 14 hours ago, captcass said: The author does not show how he derives it from HUP, but I took him at his word, as odd as it also seemed to me..... Expand It was not derived from the HUP. The author erred in claiming that.
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