Categories: Guide to Space

Is Everything in the Universe Expanding?

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.

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.

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.

Fraser Cain

Fraser Cain is the publisher of Universe Today. He's also the co-host of Astronomy Cast with Dr. Pamela Gay. Here's a link to my Mastodon account.

Recent Posts

Neutron Stars are Jetting Material Away at 40% the Speed of Light

It’s a well known fact that black holes absorb anything that falls into them. Often…

4 hours ago

Lunar Night Permanently Ends the Odysseus Mission

On February 15th, Intuitive Machines (IM) launched its first Nova-C class spacecraft from Kennedy Space…

13 hours ago

Webb Joins the Hunt for Protoplanets

We can't understand what we can't clearly see. That fact plagues scientists who study how…

16 hours ago

This Supernova Lit Up the Sky in 1181. Here’s What it Looks Like Now

Historical astronomical records from China and Japan recorded a supernova explosion in the year 1181.…

18 hours ago

Hubble Sees a Star About to Ignite

This is an image of the FS Tau multi-star system taken by the Hubble Space…

19 hours ago

This Black Hole is a Total Underachiever

Anyone can be an underachiever, even if you're an astronomical singularity weighing over four billion…

19 hours ago