We Don’t Know Universal Expansion as Well as We Think

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Conflicting Universal Expansion Data May Indicate That We Don’t Know as Much about the Universe As We Thought

We’ve known the Universe is still expanding for some time now. We thought we knew exactly how fast universal expansion is happening, too. Turns out we may be wrong, and it could have incredibly huge implications. For years, scientists have been using a number called Hubble’s constant to measure the rate at which the universe is expanding. The problem is that Hubble’s constant… well… isn’t. The concept and the original number were coined after Edwin Hubble found a linear relationship between the distance of distant objects and the rate at which they were moving away from Earth.  

According to Barry Madore, an astronomer at the University of Chicago, Hubble’s original calculations were off.

He told Live Science in an interview, “That means something spooky is going on. Why would we be the center of the universe? The answer, which is not intuitive, is that [distant objects are] not moving. There’s more and more space being created between everything.”

When scientists first realized this, they used new measurement techniques to recalculate Hubble’s constant more accurately. Hubble’s original measurements were over ten times higher than current estimates, they found. 

The Trouble With Measuring…

Madore also used an interesting race track analogy. He said that attempting to measure universal expansion is akin to walking into a race track, getting a single, short glimpse at the horses, then trying to use only that glimpse to try and figure out where the horses started and which one was going to win.

While the techniques used to measure the expanding universe are evolving, they still require a large number of assumptions. This is not unique to astrophysics, though. Nearly all of the sciences use some form of deductive reasoning or another to form hypotheses and theories. After all, when you can’t measure something directly, you have to find an indirect way to do it. 

The current controversy, which some astronomers have called a “crisis” centers on two new methods of measurement that are producing significantly conflicting results. You see, when astronomers first started revising Hubble’s constant, they did so by measuring the brightness of pulsating cepheid stars. For the last thirty years or so, that’s been the accepted method. Unfortunately, new data from the European Space Agency’s Planck satellite shows a speed that is slower than the cepheid rate by a difference of about six kilometers per second per megaparsec. The satellite uses cosmic background radiation levels to calculate Hubble’s constant.

So Who’s Right? And What’s the Big Deal, Anyway?

According to Madore, the Europeans are quite insistent that Planck’s measurements are correct, as are the physicists who’ve relied on the cepheid method for nearly three decades. Madore and his team, however, decided to use a third method of measurement in order to try and work out the difference between the two others. Instead of measuring cepheids or radiation, Madore and co. measured red giant stars, which, like cepheids produce a constant peak brightness at the end of their life cycles and allow astronomers to calculate their distance. Though he was hoping for a tie-breaker, Madore’s results were basically right in the middle.  He says the debate will likely continue for some years to come.  

The reason all of this matters is that if the new Planck numbers are right, it means we’ve been measuring the universe wrong for two generations. On the other hand, if the cepheid method is correct, then the accuracy of the Planck data implies that astronomers will need to introduce some very strange new physics into their cosmological models.  

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Brandon Humphreys

Brandon Humphreys

I'm a wizard. I write stuff and it goes from my head into yours - Magic! Apart from that, I am the Senior Editor for Space Porn, a veteran, a rock guitarist, and a teacher.

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