Gamma ray study recalculates rate of expansion of the universe

Gamma ray study recalculates rate of expansion of the universe
A new measurement of the Hubble Constant suggests the universe may be expanding slower than we thought
A new measurement of the Hubble Constant shows the universe may be expanding slower than we thought
View 1 Image
A new measurement of the Hubble Constant suggests the universe may be expanding slower than we thought
A new measurement of the Hubble Constant shows the universe may be expanding slower than we thought

Scientists generally agree that the universe is expanding, and that the rate of expansion is accelerating, but exactly how fast that’s happening is up for debate. Now, astrophysicists at Clemson University have come up with a new figure for this measure – called the Hubble Constant – by studying how gamma rays interact with the background radiation of the universe.

The Hubble Constant is named after Edwin Hubble, the astronomer who first discovered that the universe is expanding. Einstein himself had actually found this in earlier equations, but assumed he was wrong and rejigged his calculations to model a static universe. He soon conceded to Hubble, calling the assumption his greatest ever blunder.

In 1929, the first number Hubble attributed to his Constant was 500 km per second per megaparsec (km/s/Mpc) (310.7 mi/s/Mpc), where a megaparsec is about 3.26 million light-years. Basically, that means that more distant galaxies are moving away from us at faster speeds than those closer by. Since then, the Hubble Constant has been constantly refined, and in the last 20 years or so many different methods of measuring it have placed it at around 70 km/s/Mpc (43.5 mi/s/Mpc).

And now, the Clemson team has arrived at a new figure: 67.5 km/s/Mpc (41.9 mi/s/Mpc). The team came to this conclusion by analyzing data from the Fermi Gamma ray Space Telescope and Imaging Atmospheric Cherenkov Telescopes, to determine how gamma rays from distant sources are interacting with the “fog” that permeates the universe.

This fog is also known as the extragalactic background light (EBL), and it’s made up of all the ultraviolet, visible and infrared light that’s emitted by stars and other objects. When gamma rays interact with the EBL, they leave an imprint that can be analyzed to determine new clues about their long journeys – and how much longer those journeys are becoming.

“What we know is that gamma-ray photons from extragalactic sources travel in the universe toward Earth, where they can be absorbed by interacting with the photons from starlight,” says Marco Ajello, an author of the study. “The rate of interaction depends on the length that they travel in the universe. And the length that they travel depends on expansion. If the expansion is low, they travel a small distance. If the expansion is large, they travel a very large distance. So the amount of absorption that we measured depended very strongly on the value of the Hubble Constant. What we did was turn this around and use it to constrain the expansion rate of the universe.”

The new measurement of 67.5 km/s/Mpc means the universe may be expanding slower than is generally believed. In 2012, for instance, a study using the Spitzer Space Telescope calculated the Hubble Constant to be 74.3 km/s/Mpc (46.2 mi/s/Mpc). Another, using Hubble’s namesake space telescope, put the number at 73.2 km/s/Mpc (45.5 mi/s/Mpc).

While the slight change won’t really mean much to the average person here on Earth, refining the Hubble Constant is important in understanding the universe’s past, present and future.

“The astronomical community is investing a very large amount of money and resources in doing precision cosmology with all the different parameters, including the Hubble Constant,” says Dieter Hartmann, an author of the study. “Our understanding of these fundamental constants has defined the universe as we now know it. When our understanding of laws becomes more precise, our definition of the universe also becomes more precise, which leads to new insights and discoveries.”

The research was published in the Astrophysical Journal.

Source: Clemson University

What does this mean as a figure for acceleration? The value given appears to be given as a speed and not as an acceleration.
What would this be as an acceleration that makes sense on earth, like in ft per second squared? I wonder what the effect of this would be in terms of the equivalence principle, i.e how many G's would this represent?
To partly answer the question from Altronix, the Hubble constant is already a measure of acceleration. Perhaps the easiest way to see this is to note that a mega-parsec is ALSO a measure of time; looking far away is also looking back in time. So "km/sec" is clearly speed and "speed over time" is acceleration. All the excitement is about all the different numbers we are getting from different ways to measure the Hubble constant. Quite possibly, it is NOT a constant. But how and why it changes is unexplained. Scientists are always see exciting opportunity when something is unexplained.
There's quite a lot of mass in the Universe, if it is accelerating apart, presumably that requires an ever-increasing amount of energy...
Expansion with an increasing rate of expansion is simply 1/4 if a Sine Wave. That wave has properties of wave and particle, just like everything else. The wave action is the Dark Energy and the particle property is the Dark Matter. The particle property of the gravity wave IS the Higgs and what limits the speed of light. Black holes just recycle everything back to the gravity wave, with a wave length around 5 trillion light years. Simple as pie. There was no big bang, there was no "beginning". Infinite Wave Theory, perfect, works with everything we know. Get you nose off the billboard if you want to read it:)
Given that nothing being measured is where it was billions of years ago and may not even exist today, I don't think they will ever come up with an accurate Hubble Constant, if one even exists.
Maboomba Maboomba
I continue to suspect the "expanding universe" could be an illusion similar to our previous thinking that the sun goes up and down around a central earth.
Both seem obvious and undeniable - you're looking right at it - completely "straightforward" and "unarguable", until you get to the next step in understanding.
That's how science rolls: yesterday's 100% certainty is tomorrow's "Whoops, we had it wrong".