How fast is the universe expanding?

February 10, 2015 by Brian Koberlein, Universe Today
Artists illustration of the expansion of the Universe. Credit: NASA, Goddard Space Flight Center

The Universe is expanding, but how quickly is it expanding? How far away is everything getting from everything else? And how do we know any of this anyway?

When astronomers talk about the expansion of the Universe, they usually express it in terms of the Hubble parameter. First introduced by Edwin Hubble when he demonstrated that more distant galaxies are moving away from us faster than closer ones.The best measurements for this parameter gives a value of about 68 km/s per megaparsec.

Let's recap. Hubble. Universe. Galaxies. Leaving. Further means faster. And then I said something that sounded like "blah blah Lando blah blah Kessel Run 68 km/s per megaparsec". Which translates to if you have a galaxy 1 megaparsec away, that's 3.3 million light years for those of you who haven't seen Star Wars, it would be expanding away from us at a speed of 68 km/s. So, 1 megaparsec in distance means it's racing away at 68 km/s.

This is all because space is expanding everywhere in all places, and as a result distant galaxies appear to be expanding away from us faster than closer ones. There's just more "space" to expand between us and them in the first place. Even better, our Universe was much more dense in the past, as a result the Hubble parameter hasn't always had the same value.

There are two things affecting the Hubble parameter: dark energy, working to drive the Universe outwards, and matter, dark and regular flavor trying to hold it together. Pro tip: The matter side of this fight is currently losing.

Earlier in the Universe, when the Hubble parameter was smaller, matter had a stronger influence due to its higher overall density. Today is dominant, thus the Hubble parameter is larger, and this is why we talk about the Universe not only expanding but accelerating.

Our cosmos expands at about the rate at which space is expanding, and the speed at which objects expand away from us depends upon their distance. If you go far enough out, there is a distance at which objects are speeding away from us faster than the speed of light. As a result, it's suspected that receding galaxies will cross a type of cosmological event horizon, where any evidence of their existence, not even light, would ever be able to reach us, no matter how far into the future you went.

What do you think? Is there anything out there past that cosmological event horizon line waiting to surprise us?

Expansion of the Universe. Credit: Eugenio Bianchi, Carlo Rovelli & Rocky Kolb.

Explore further: Why is Andromeda coming toward us?

Related Stories

Why is Andromeda coming toward us?

January 23, 2015

I don't want to alarm you, but there's a massive galaxy heading our way and will collide with us in a few billion years. But aren't most galaxies speeding away? Why is Andromeda on a collision course with the Milky Way?

Is the universe actually shrinking?

February 3, 2015

Whoa, here's something to think about. Maybe the Universe isn't expanding at all. Maybe everything is actually just shrinking, so it looks like it's expanding. Turns out, scientists have thought of this.

Image: Hubble sees spiral in Serpens

September 8, 2014

(Phys.org) —This new NASA/ESA Hubble Space Telescope image shows a beautiful spiral galaxy known as PGC 54493, located in the constellation of Serpens (The Serpent). This galaxy is part of a galaxy cluster that has been ...

Hubble image: A cross-section of the universe

April 17, 2014

An image of a galaxy cluster taken by the NASA/ESA Hubble Space Telescope gives a remarkable cross-section of the Universe, showing objects at different distances and stages in cosmic history. They range from cosmic near ...

Recommended for you

The atmospheres of water worlds

October 23, 2017

There are currently about fifty known exoplanets with diameters that range from Mars-sized to several times the Earth's and that also reside within their stars' habitable zone – the orbital range within which their surface ...

Dawn mission extended at Ceres

October 20, 2017

NASA has authorized a second extension of the Dawn mission at Ceres, the largest object in the asteroid belt between Mars and Jupiter. During this extension, the spacecraft will descend to lower altitudes than ever before ...

14 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

mscheue1
1 / 5 (1) Feb 10, 2015
Hubble surmised that the universe was expanding because the night sky was black. As the author points out, this expansion rate has been measured at 68 km/s. I wonder how much slower the expansion rate would have to be to turn the night sky light. Zero expansion obviously works but some expansion would, too, if the production rate of photons escaping stars balanced the increasing volume of space.
Losik
Feb 10, 2015
This comment has been removed by a moderator.
Losik
Feb 10, 2015
This comment has been removed by a moderator.
Glaufx Garland
1 / 5 (4) Feb 10, 2015
Expanding to where? = the universe can not expand beyond itself because is one and only one and no more - there is no other or there will not be another -there is no up down or far beyond universe and that is because it is endless and non created = non-created and without end -Pro-Platonic philosophy 3000 years ago and maybe more
Glaufx Garland
1 / 5 (4) Feb 10, 2015
Expanding to where? = the universe can not expand beyond itself because is one and only one and no more - there is no other or there will not be another -there is no up down or far beyond universe and that is because it is endless and non created = non-created and without end -Pro-Platonic philosophy 3000 years ago and maybe more
movementiseternal
Feb 10, 2015
This comment has been removed by a moderator.
Tuxford
1 / 5 (5) Feb 10, 2015
Zero. Not expanding, as there was no Huge Bang, and the universe is simply old. Tired light explains the red shift, as will eventually be acknowledged when physicists are sufficiently discredited with their obsolete, tired theories.
fourinfinities
2 / 5 (4) Feb 10, 2015
For comparison, the Moon's orbit is expanding at about 100 km/s per megaparsec...and accelerating!
LuisMarco
1 / 5 (3) Feb 11, 2015
'The URANTIA Papers' 5th epochal divine Revelation gives a revelation for this, at least generally: the respiration cycle of all space; google urantia if you will! :)
movementiseternal
Feb 11, 2015
This comment has been removed by a moderator.
reset
2.3 / 5 (3) Feb 11, 2015
Does the theory of expanding space explain why it is only cosomological space which is expanding, in other words why matter is exempt from this expansion so that we can measure the effect? Just asking because if all space is expanding then the relative distance between objects wouldn't change.

@Movement - Congratulations on finally seeing the word "expanding" mentioned in an article. Your star is rising.
wduckss
1.8 / 5 (5) Feb 13, 2015
The expansion of the Universe is only a misconception from the beginning of the last century. The universe is like a globular cluster, without prominent center, which rotates more slowly than the body that is moving away from the center. As with the cluster velocity at the orbit of the "surface" is the greatest.
That exist photons they would lit up and out of the body, svermir would then be bright ...
Benni
1 / 5 (2) Feb 13, 2015
Expanding to where? = the universe can not expand beyond itself because is one and only one and no more - there is no other or there will not be another -there is no up down or far beyond universe and that is because it is endless and non created = non-created and without end -Pro-Platonic philosophy 3000 years ago and maybe more

Yeah, if the universe is already "infinite in size" it can't get any bigger, & if it can't get any bigger then how can it expand to something greater than it's present infinite size because it would have nowhere to expand to.
Johnpaily
1 / 5 (2) Feb 18, 2015
Universe expanding and contracting is illusions - Recent development in Quantum science has proved it - what is expanding and contracting is consciousness and intelligence -https://www.scrib...-Process

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.