# How fast is the universe expanding?

#### Magical Realist

Valued Senior Member
I googled this a got a ridiculously complicated answer. In layman's terms, what is the rate of the universe's expansion? And how long till we can detect it physically?

I googled this a got a ridiculously complicated answer. In layman's terms, what is the rate of the universe's expansion? And how long till we can detect it physically?

Whatever you got from Google was in laymen's terms. The rate is increasing. What do you mean by "detect it physically"? Red-shifting is a physical effect.

Are you wondering when you will see Mars moving away from Earth due to expansion (for example)? That's not how it works. Our Solar System is gravitationally bound. That's not what is expanding.

In layman's terms, what is the rate of the universe's expansion?
Hubble's constant is about 60km/s/Mpc which means that things one megaparsec apart are separating at an average of about 60kps and things two megaparsecs apart are going apart at 120kps and things three megaparsecs away are moving apart at 180kps etc etc.
And how long till we can detect it physically?
How do you reckon we know about it if we can't detect it physically? Redshift measures are physical measurements.
Are you wondering when you will see Mars moving away from Earth due to expansion (for example)? That's not how it works.
There are some models of dark energy called quintessence that do lead to this happening and ripping apart everything even atoms eventually. It's called the Big Rip but it's on the fringe of mainstream because the physical characteristics of quintessence are pretty implausible but not strictly ruled out yet. I don't remember what the possible timescales for total destruction are but the Sun'll be dead and gone long before.

In layman's terms, what is the rate of the universe's expansion?
Faster than little green aliens can travel in their UFOs to visit us

What do you mean by "detect it physically"? Red-shifting is a physical effect.

I was thinking along the lines of our atoms being torn apart. Something SSS addressed in their post.

I was thinking along the lines of our atoms being torn apart. Something SSS addressed in their post.
In that case never because that's not how expansion works unless quintessence turns out to be a correct theory which isn't very likely IMO.

I was thinking along the lines of our atoms being torn apart. Something SSS addressed in their post.
No. Cosmological Expansion does not affect gravitationally bound objects, let alone atomically bound objects.

Not only is our galaxy immune from CE, but even our local cluster is essentially immune.

Glue some pennies to a balloon. Inflate the balloon. The pennies get farther apart but they do not get larger, or get pulled apart.

No. Cosmological Expansion does not affect gravitationally bound objects, let alone atomically bound objects.

Not only is our galaxy immune from CE, but even our local cluster is essentially immune.

Glue some pennies to a balloon. Inflate the balloon. The pennies get farther apart but they do not get larger, or get pulled apart.

But there is space in between our atoms, and a lot of it relative to them. Why wouldn't that space be expanding too?

"Some days, you might feel like a pretty substantial person. Maybe you have a lot of friends, or an important job, or a really big car.

But it might humble you to know that all of those things – your friends, your office, your really big car, you yourself, and even everything in this incredible, vast Universe – are almost entirely, 99.9999999 percent empty space."--- https://www.sciencealert.com/99-9999999-of-your-body-is-empty-space

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The Big Freeze is the most likely outcome. The expansion continues but everything is so far apart that there is essentially no movement (time stops in effect if nothing changes) and temperature is as low as it can get...therefore the Big Freeze.

But there is space in between our atoms, and a lot of it relative to them. Why wouldn't that space be expanding too?

"Some days, you might feel like a pretty substantial person. Maybe you have a lot of friends, or an important job, or a really big car.

But it might humble you to know that all of those things – your friends, your office, your really big car, you yourself, and even everything in this incredible, vast Universe – are almost entirely, 99.9999999 percent empty space."---
Before the strong force has a much greater effect than the expansion.

But there is space in between our atoms, and a lot of it relative to them. Why wouldn't that space be expanding too?
Thats why I posted the example of the balloon. You dont expect the balloon to rip the pennies apart do you? The bond between atoms is far stronger than the balloon's weak pull.

It is not really good to think of it as "space" expanding; it is really better described as "large scale things are getting farther apart".

Before the strong force has a much greater effect than the expansion.

There is a small, only a few billion atoms, lump of stuff zooming away from every other lump of stuff until every other lump of stuff is so distant it has no gravitational attraction acting on it

Will its atoms begin to spread apart from each other until it could be described as "cluster of atom move in close formation?"

What happens to the energy holding the formation together as formation expands?

Will its atoms begin to spread apart from each other until it could be described as "cluster of atom move in close formation?"
No.

It's a bit like asking if you and your girlfriend, holding hands while walking, will get your arms stretched due to the effect of continental drift - but many, many times exaggerated. The mechanics of the local scale utterly, utterly overcomes the mechanics of the cosmic scale.

"But, in theory, if we walk long enough and both walk perfectly straight, we will eventually drift apart." you say.

Really? How exactly can you drift apart if you are holding hands?

What happens to the energy holding the formation together as formation expands?
No energy is holding them together. They started off on parallel trajectories.

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But there is space in between our atoms, and a lot of it relative to them.
That's kinda arguable because QM says the electron wavefunctions are spread out over the volume of the atom and are usually overlapped with nearby ones so there isn't really space between. People argue about whether wavefunctions are real things or not though so maybe.
Why wouldn't that space be expanding too?
That's not how it works. Space isn't a thing that's expanding anything it's just a convenient way to describe what happens in a simple model of the large scale universe. It doesn't work at small scales because some bits of the universe are more dense than others and the denser parts have enough gravity to stop the flying apart.

Will its atoms begin to spread apart from each other until it could be described as "cluster of atom move in close formation?"
No not unless quintessence turns out to be real.

How exactly can you drift apart if you are holding hands?
Maybe they're just better as friends.

Before the strong force has a much greater effect than the expansion.

I never could agree this explaination (i agree this is the official explaination with the so sayed "gravitationally bounded objects")
If i have 2 forces acting on some obect i can not say the second force doesent exists because the first is stronger.

If i have 2 forces acting on some obect i can not say the second force doesent exists because the first is stronger.
If you think that's what scientists say then you have catastrophically misunderstood whatever you read or else it was a BS source.