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Ask Ethan: Could ‘Cosmic Redshift’ Be Caused By Galactic Motion, Rather Than Expanding Space?

23 Mar 2019, 14:01 UTC
Ask Ethan: Could ‘Cosmic Redshift’ Be Caused By Galactic Motion, Rather Than Expanding Space?
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The impressively huge galaxy cluster MACS J1149.5+223, whose light took over 5 billion years to reach us, was the target of one of the Hubble Frontier Fields programs. This massive object gravitationally lenses the objects behind it, stretching and magnifying them, and enabling us to see more distant recesses of the depths of space than in a relatively empty region. The lensed galaxies are among the most distant of all, and can be used to test the nature of redshift in our Universe. (NASA, ESA, S. RODNEY (JOHN HOPKINS UNIVERSITY, USA) AND THE FRONTIERSN TEAM; T. TREU (UNIVERSITY OF CALIFORNIA LOS ANGELES, USA), P. KELLY (UNIVERSITY OF CALIFORNIA BERKELEY, USA) AND THE GLASS TEAM; J. LOTZ (STSCI) AND THE FRONTIER FIELDS TEAM; M. POSTMAN (STSCI) AND THE CLASH TEAM; AND Z. LEVAY (STSCI))Both effects could be responsible for a redshift. But only one makes sense for our Universe.In physics, like in life, there are often multiple solutions to a problem that will give you the same result. In our actual Universe, however, there’s only one way that reality actually unfolds. The great challenge that presents itself to scientists is to figure out which one of the possibilities that nature allows ...

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