• Question: Light from distant source in observable universe reaches us in 13.75 billion light years; could redshift be caused by 'tired' light and not an expanding universe? Light cannot have infinite energy so it must slow or stop?

    Asked by waveicle to Adam, Sheila on 25 Mar 2011 in Categories: .
    • Photo: Adam Tuff

      Adam Tuff answered on 25 Mar 2011:

      This was proposed by Fritz Zwicky, who I am quite fond of as he’s probably the father of the dark matter concept! The problem with the tired light solution is that it doesn’t quite fit with the observables, such as fit the observed redshifts we see from recessional objects, explain time dialation etc…so far no model has been proposed that better’s General relativity. There were ideas for “gravitational drag”, but again I think they suffer from lack of mechanisms.

    • Photo: Sheila Kanani

      Sheila Kanani answered on 25 Mar 2011:

      I like your thinking around this question!

      However, photons are massless and only travel at the speed of light, so would not slow down or ‘tire’.

      Energy is calculated using the formula E= mc^2.

      If the mass is infinite, Energy is infinite, But the speed of the photon is still c.

      It requires infinite energy to accelerate an object with mass to the speed of light.

      Massless entities however, can easily travel at the speed of light, because the energy required to accelerate something to great speed, is mostly reliant on the mass of the object.

      Light and radiation has no mass, so it can move at the speed of light.

      So I think until we find out that photons have mass, we can assume that redshift it real!

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