The most modern definition of the meter

[mahela007]

What is the currently used definition of the meter? (meter, as in the unit of measuring length..)

Someone told me that, if wavelengths of all the emission frequencies of an atom were added together the total length would be a meter. Is that true? I haven't found any reference to that definition anywhere else...

[insane_alien]

the current definition of a meter is how far a photon of light travels in 1⁄299,792,458 of a second in a vacuum.

 

the thing about emission frequencies from an atom is completly rubbish. there is nothing stting that they will add up to a meter and since the nuclei have emission frequencies in the RF spectrum with several hundred meter wavelengths it is certainly wrong.

 

and emmissions from the electron shell would add up to only a few millionths of a meter. perhaps a millimeter.

[mahela007]

Thanks.. Even to me, the thing about the emission wavelengths sounded a bit far fetched.... but I'm still at an introductory level of physics so I had to clarify.. thanks again!

[timo]

and emmissions from the electron shell would add up to only a few millionths of a meter. perhaps a millimeter.

Or towards infinity:

1) In classical QM there is an infinite number of energetically-distinct orbitals for the hydrogen atom => there is an infinite number transitions from excited orbitals to the ground state => there is an infinite number of possible transitions for the hydrogen atom alone.

2) All these transitions are bound to release an energy < 13.7 eV => All the corresponding wavelengths of the transitions are greater than some threshold wavelength.

(1) + (2) => There is no finite result.

[insane_alien]

ah right, i was just thinking of the jumps between shells sorry.

[mahela007]

so was I..

[swansont]

What is the currently used definition of the meter? (meter, as in the unit of measuring length..)

Someone told me that, if wavelengths of all the emission frequencies of an atom were added together the total length would be a meter. Is that true? I haven't found any reference to that definition anywhere else...

 

One definition that has a tiny bit of relevance — meaning it mentions wavelength of an emission — is when the meter was defined in terms of a Krypton transition: 1,650,763.73 wavelengths of a particular transition in Kr-86. That was the definition from 1960 until 1983.

[timo]

ah right, i was just thinking of the jumps between shells sorry.

so was I..

I then possibly do not understand what you guys mean.

I was talking about jumps between shells. In particular I only considered the subset of jumps from an excited state to the ground state. If you consider jumps form n+1 to n (n being the main quantum number) the issue becomes even worse because the wavelength of the individual jumps then also diverges as n increases. Perhaps I was missing explicitly saying that if a subset of possible emission wavelength already does not lead to a finite sum that then whole set does not, either?

[insane_alien]

i suspect it is my amatuer knowledge of quantum mechanics. i thought there were a limited number of excited states before the electron was ejected.