Is Everything in the Universe Expanding?

by Fraser Cain on December 12, 2013

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The Universe is expanding. Distant galaxies are moving away from us in all directions. It’s natural to wonder, is everything expanding? Is the Milky Way expanding? What about the Solar System, or even objects here on Earth. Are atoms expanding?

Nope. The only thing expanding is space itself. Imagine the Universe as loaf of raisin bread rising in the oven. As the bread bakes, it’s stretching in all directions – that’s space. But the raisins aren’t growing, they’re just getting carried away from each other as there’s more bread expanding between them.

Space is expanding from the Big Bang and the acceleration of dark energy. But the objects embedded in space, like planets, stars, and galaxies stay exactly the same size. As space expands, it carries galaxies away from each other. From our perspective, we see galaxies moving away in every direction. The further galaxies are, the faster they’re moving.

There are a few exceptions. The Andromeda Galaxy is actually moving towards the Milky Way, and will collide with us in about 4 billion years.In this case, the pull of gravity between the Milky Way and Andromeda is so strong that it overcomes the expansion of the Universe on a local level.

The Andromeda Galaxy will collide with the Milky Way in the future. Credit: Adam Evans

The Andromeda Galaxy will collide with the Milky Way in the future. Credit: Adam Evans

Within the Milky Way, gravity holds the stars together, and same with the Solar System. The nuclear force holding atoms together is stronger than this expansion at a local scale. Is this the way it will always be? Maybe. Maybe not.

A few decades ago, astronomers thought that the Universe was expanding because of momentum left over from the Big Bang. But with the discovery of dark energy in 1998, astronomers realized there was a new possibility for the future of the Universe. Perhaps this accelerating dark energy might be increasing over time.

In billions years from now, the expansive force might overcome the gravity that holds galaxies together. Eventually it would become so strong that star systems, planets and eventually matter itself could get torn apart.This is a future for the Universe known as the Big Rip. And if it’s true, then the space between stars, planets and even atoms will expand in the far future.

This image shows the Hubble Ultra Deep Field 2012, an improved version of the Hubble Ultra Deep Field image featuring additional observation time. The new data have revealed for the first time a population of distant galaxies at redshifts between 9 and 12, including the most distant object observed to date. These galaxies will require confirmation using spectroscopy by the forthcoming NASA/ESA/CSA James Webb Space Telescope before they are considered to be fully confirmed.

The space between the galaxies is expanding. Credit: NASA/HST

Is this going to happen? Astronomers don’t know. Their best observations so far can’t rule it out, or confirm it. And so, future observations and space missions will try to calculate the rate of dark energy’s expansion.

So no, matter on a local level isn’t expanding. The spaces between planets and stars isn’t growing. Only the distances between galaxies which aren’t gravitationally bound to each other is increasing. Because space itself is expanding.

About 

Fraser Cain is the publisher of Universe Today. He's also the co-host of Astronomy Cast with Dr. Pamela Gay.

«Harvey Esquire» December 13, 2013 at 9:15 AM

I have heard on various TV shows, about the universe, that space is expanding FASTER than the speed of light. This does not seem logical. If it is true, does this suggest that the speed of light can be broken under the right conditions?

IVAN3MAN_AT_LARGE December 13, 2013 at 12:15 PM

I think of it this way: two cars pass each other in opposite directions on a freeway, travelling at the speed limit of 70 m.p.h. (relative to the road); the space between them will appear to be expanding at (2×70) 140 m.p.h.

Heterosexual Bruno December 14, 2013 at 2:38 PM

If all galaxies happen to be pulled apart by expanding space from the beginning how come Andromeda and Milky Way are on collision course? In order for local gravity to be stronger than effect of Hubble expansion they had to be on collision course right after their formation, which contradicts the Big Bang Theory, as local pockets of forming matter had to be separated by large distances and rapidly expanding space already in the early Universe.

deryk houston December 15, 2013 at 1:53 PM

I am excited about the theory presented by Ling Jun Wang …… An Alternative Cosmology to the Big Bang–Dispersive Extinction Theory of Red Shift.
It boggles the mind that the Big bang is still the leading theory despite the large number glaring problems with it.

So far I haven’t read anything that debunks Wang’s theory. His theory does not require a lot of sticking plasters to hold it all together….. like the Big bang theory requires.
I look forward to seeing how the “Dispersive Extinction Theory” holds up with more observations.
Supporters of the Big Bang are going to look like complete fools I believe.

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