Blog of Veikko M.O.T. Nyfors, Hybrid Quantum ICT consultant

Quantum Mechanics demystified, a try

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About redshift

Have you ever pondered how do they deduce what’s the distance to some star or galaxy is. They say it can be told from redshift of the light from that source. What’s the redshift method based on, I wonder.

Basic assumption is that a star, galaxy or any cosmological object is spreading frequencies of electromagnetic radiation in specific proportions. Radiation is caused by heat produced in fusion reactions, fusion being mostly that of hydrogen turning to helium. There is some other types of fusions also taking place in stars, but mainly in older stars and stars close to their end life.

Key for understanding redshift’s logic is that certain frequencies are absorbed from the radiation by hydrogen and helium atoms. These frequencies are ones that make electrons jump to higher energy levels on those atoms. Those frequencies are known by having been determined by laboratory experiments. When this radiation is targeted to a prism, the spectrum produced has darker lines on spots for those frequencies.

But now, anyway, when the radiation is traveling towards us, the universe is spreading out at the same time. This makes the wave length appear longer to us when perceived. Speed of radiation remains constant c, but as we travel further away from the source all the time, peaks and troughs of radiation get further away. I.e. wave length increases, turning the radiation to shift a bit to the red side of the spectrum. Originally blue light turns first green and then further to other colours towards red.

If the universe would spread in a steady speed, the amount of red shift would always be the same. Just as the sound of ambulance’s siren moving away from you remains the same.
However, if the ambulance would be accelerating, the sound would become lower and lower, as the wave length increases.
Exactly the same happens with our universe spreading in accelerating speed. Radiation frequency from far away cosmological objects gets lower the longer the radiation has been on the way.
Thus, by routing star’s radiation through prism and noting the frequencies of the darker spots, we can see amount of redshift. By knowing the acceleration, we then can calculate how long the radiation has been on the way together with the distance of the object.

How the acceleration of the spreading of the universe is determined, that’s not quite clear to me yet. Somehow I think it’s connected to realization of the change of redshift from the same object over time. If so, we might have the hen and egg problem in hand. Which one was first?