Using redshift, distance to a type 1A supernova can be estimated. Using standard candle luminosity, distance to a type 1A supernova can be estimated. Astronomical observation found luminosity of type 1A SN 25% dimmer than expected? If that implies the type 1A SN are further than redshift suggests, then presumably the same type 1A SN is at one and the same time at two different distances from Earth, the redshift distance and the luminosity distance. Where is the logical error?
Dear Robert,
There are two aspects of the answer to your question.
First, SNe Ia are 25% dimmer than the expectation derived from the model of the Universe expanding at a constant speed. This is how we learnt that the Universe is in fact accelerating. Hence, you may say that what you refer to as "redshift distance" is simply wrong, because to derive it one assumed no acceleration.
Second, you need to be careful when you compare distances in cosmology. The space is expanding, so the luminosity distance is not the same as the proper distance (or other distance measures!), because the former relates to light travelling from a source, but during this travel the Universe is also expanding. Hence, you shouldn't say that a given source is at two different distances at a given time (luminosity distance and proper distance), but that you need to define what you mean by "distance" and the value will depend on your definition.
A somewhat imperfect analogy would be to ask a question: what is the speed of a plane? A radar on the surface of the Earth measures 500 km/s, whereas the pilot measures 510 km/s, because he measured it with respect to the surrounding air and the wind blows with the speed of 10 km/s against the plane (this is probably not how they do it in reality). You wouldn't say that the plane moves with two different speeds, but that the value depends on how you define it - relative to the Earth or the air?
Hope this helps,
Michał
Dr Michalowski
My point of view seems to be somewhat similar to yours.
There is one distance but there are two reference frames. Thus the distance that light travels gives a result in the redshift reference frame, as it were, that is different from the luminosity reference frame.
The different distances imply the real existence of two reference frames. As if thete are two co-existing universe. While that seems a bit weird to me, it is much less weird than the idea of a multiverse.
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