Physics World July 2020

Hubble trouble: why we can’t decide how fast the universe is expanding

Europe’s Planck mission measured the Hubble constant to the greatest precision ever, finding it to be 67.4 km/s/Mpc, with an uncertainty of less than 1%. So how come more recent measurements of our “local universe” yield a figure of 73.3 km/s/Mpc, with an uncertainty of 2.4%, suggesting the universe is not as old as we thought? Keith Cooper investigates the discrepancies and what the implications could be. Meanwhile, Rachel Brazil explores why flat-earth theory is increasingly taking hold and how the physics community should best respond. Also, James McKenzie marvels at the wonders of e-bikes, and Richard Stevenson looks at powerful new blue lasers that can produce high-quality copper welds needed to make batteries for electric vehicles more easily.

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