# Time measurement

bassplayer142
After I realized that relativity slowed and speeds up time relative to the frame of reference I realized that time is not absolute. Why would we continue to measure time as the vibration of an atom. Wouldn't we start measuring time by the vibration of a photon? Since a photon is absolute no matter where in the universe it is and it stays constant for that wavelength.

rbj
After I realized that relativity slowed and speeds up time relative to the frame of reference I realized that time is not absolute. Why would we continue to measure time as the vibration of an atom. Wouldn't we start measuring time by the vibration of a photon? Since a photon is absolute no matter where in the universe it is and it stays constant for that wavelength.

which photon would you choose as a standard for a unit of time?

be very careful answering that. if you say "photons of blue visable light" then i would ask how you define blue? if blue photons are the photons that make it through some standardized blue filter, then you're back to defining this in terms of the atoms of some material.

bernhard.rothenstein
measuring time

After I realized that relativity slowed and speeds up time relative to the frame of reference I realized that time is not absolute. Why would we continue to measure time as the vibration of an atom. Wouldn't we start measuring time by the vibration of a photon? Since a photon is absolute no matter where in the universe it is and it stays constant for that wavelength.

Why not measure time using as an unit the period of the electromagnetic oscillations taking place in the electromagnetic wave in which we are immersed? Besides that we should now which kind of time interval we measure: proper time or coordinate time.

eigenglue
To measure time, you need photons of known fixed wavelength, so that you know the frequency. If you are moving in reference to the source, that changes the frequency (doppler effect), but that's not a problem in atomic clocks. So you use a specific atomic vibration, with a specific energy, to generate the photons of fixed frequency.

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Gold Member
which photon would you choose as a standard for a unit of time?
To measure cosmological time:

Select a photon sampled from the peak emission intensity of the CMB corrected for the Earth's dipole movement.

Then the universe woul be eternal, and if c is defined constant and used to measure radar distance, the universe would also be static, as in the Jordan conformal frame of http://en.wikipedia.org/wiki/Self-creation_cosmology [Broken].

Garth

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bassplayer142
I guess your right about the doppler effect. It just doesn't seem right to measure time with something that changes.

nakurusil
I guess your right about the doppler effect. It just doesn't seem right to measure time with something that changes.

You don't get any Doppler effect if you are not moving wrt the source. In metrology, your clock is supposed to be infinitely small and to lie at rest no farther away from your elbow. So, no Doppler effect, of ny sort.