Is the Universe Expanding or Has it Already Expanded?

[Lino]

Thanks George. (Kinda understand and just the info I was looking for.)

Regards,

Noel.

 

[mufa]

De Broglie equation has experimentally confirmed.Why we have to reject the hypothesis photon have a mass instead of the possibility being wrong the relativistic formula for energy?

 

[bapowell]

De Broglie equation has experimentally confirmed.Why we have to reject the hypothesis photon have a mass instead of the possibility being wrong the relativistic formula for energy?

Because experiments have failed to detect a photon mass greater than 10^{-27} eV (see http://en.wikipedia.org/wiki/Photon#Experimental_checks_on_photon_mass.)

 

[harve]

No. The simplest way to think of a photons is as a short burst of waves encapsulated in a form that can only interact as if it was a particle, i.e. all or nothing. It's equivalent to thinking of it as a particle which has an intrinsic phase which changes at a rate given by its angular frequency.
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George,I read your posts.Can you explain to me what an elegtromagnetic pulse is? Because I thought that is a wave with only one peak represents a big quantity of photons.

 

[Landrew]

My confusion comes from whether objects in space are moving apart, or whether space itself is getting larger. The distinction seems less than clear in most discussions I've seen.

http://en.wikipedia.org/wiki/Accelerating_universe
http://en.wikipedia.org/wiki/Metric_expansion_of_space

 

[Whovian]

My confusion comes from whether objects in space are moving apart, or whether space itself is getting larger. The distinction seems less than clear in most discussions I've seen.

http://en.wikipedia.org/wiki/Accelerating_universe
http://en.wikipedia.org/wiki/Metric_expansion_of_space

They're indistinguishable, it's just more convenient to think of it as space expanding.

 

[GeorgeDishman]

Doppler effect appears in waves produced by oscillators witch have “peaks” and “hollows”. These peaks can be condensed or diluted by the Doppler effect. In the light case, a peak represents an amount of photons

No. The simplest way to think of a photons is as a short burst of waves encapsulated in a form that can only interact as if it was a particle, i.e. all or nothing. It's equivalent to thinking of it as a particle which has an intrinsic phase which changes at a rate given by its angular frequency.

George,I read your posts.Can you explain to me what an electromagnetic pulse is? Because I thought that is a wave with only one peak represents a big quantity of photons.

I've added some context as the quotes are quite old.

A single pulse has a DC component so can't be a simply EM signal in space say. If it was a switched DC signal on a wire, you'd have to look at the components of the Poynting Vector and it all gets complicated, however I understand what you are asking. You can consider instead a rectangular wave with narrow, widely separated pulses and zero average value.

A square pulse is the sum of many sine waves, you can get the pattern by taking a Fourier Transform. For a regular series of pulses there are discrete harmonics while for a single pulse you get a continuous spectrum. Either way, you can then break down each sine wave into numbers of photons by dividing the portion of the pulse energy in that frequency by the energy of a single photon. As you say, ultimately you will get a burst of photons but of a mixture of frequencies. Again, each photon can be thought of as a burst of waves and they overlap to create the macroscopic, measurable, sine wave.

That's very different to what the O.P. was saying, that "a peak [of a sine wave] represents an amount of photons".