Serious question about the expansion of space.

[BoJangles2]

Question about the expansion of space.

If space is expanding, how much does space expand on the scale of a meter/kilometer over a year?

Note: I realise gravity negates the expansion of space in regaurds to mass and particles on smaller scales, but knowing that space is still expanding anyway, how much does space expanding on the scale of a meter/kilometre in a year.

Would it be like a micrometer every year or something, what’s the maths here?

And as a supplementary question, would it be possible to set up a terrestrial experiment to measure this expansion? or is it the case of A) equipment not being sensitive enough or B), we don’t know what to measure C) Physics can’t measure said phenomenon on this scale. D) the question is wrong

Thanks for your time in advance and look foward to being burnt at the theortetical phsyics stake.

 

[derekmcd]

A quick calculation tells me it is a few orders of magnitude smaller than the radius of a proton per kilometer per second. In other words, no terrestrial lab is going to be able to isolate a couple test particles free from other forces to measure something that small.

At least, not in the foreseeable future.

 

[BoJangles2]

Thanks derekmcd, allways helpfull

 

[derekmcd]

I just got home from work and thought I would get a bit more exact. I'm doing some rounding for easier calculations.

If we take the Hubble constant to be 70km per megaparsec per second, we have an expansion of 7 * 10^4 meters every 3 * 10^22 meters every second.

If we want to find out how that translate into expansion per kilometer, we simply divide as such:

7*10^4 / 3*10^22

We end up with 2.33 * 10^-18... quite the small number.

The radius of a proton is about 9*10^-16 meters. We are looking at an expansion, within a single kilometer, between 1-2 orders of magnitude smaller than the radius of a proton.

I don't feel like following through with the rest of the math, but it would take a device about 30 kilometers in length to detect the expansion the size of a proton. Even if we could build such a device, free from all forces, the mere act of observing it (you would likely need bounce photons off what you were measuring) would skew the results.

 

[DrRocket]

I just got home from work and thought I would get a bit more exact. I'm doing some rounding for easier calculations.

If we take the Hubble constant to be 70km per megaparsec per second, we have an expansion of 7 * 10^4 meters every 3 * 10^22 meters every second.

If we want to find out how that translate into expansion per kilometer, we simply divide as such:

7*10^4 / 3*10^22

We end up with 2.33 * 10^-18... quite the small number.

The radius of a proton is about 9*10^-16 meters. We are looking at an expansion, within a single kilometer, between 1-2 orders of magnitude smaller than the radius of a proton.

I don't feel like following through with the rest of the math, but it would take a device about 30 kilometers in length to detect the expansion the size of a proton. Even if we could build such a device, free from all forces, the mere act of observing it (you would likely need bounce photons off what you were measuring) would skew the results.

I have not checked your arithmetic, but I trust you, so the 'strain' of space would be the pure number 2.33*10^-18, so in a kilometer the extension would be 2.33*1010^-15 meters or a little more than the diameter of a proton -- still kind of small. So complicate matters further in a gravitationally bound location (like a lab on earth) the effect would be smaller, and in fact non-existent since the force of expansion is countered by the forces of gravity, electromagnetism, and the strong and weak forces and things are in equilibrium.

A good general relativist might be able to think of a way to do this with spacecraft, but I don't see it at the moment.

 

[BoJangles2]

Thanks guys, pretty small numbers indeed, instincitivly i thought they would be a little bigger, ahh well.

 

[MeteorWayne]

A related point I didn't see mentioned...

Full article here:

http://www.astronomy.com/asy/default.aspx?c=a&id=8248

"May 7, 2009
Whatever dark energy is, explanations for it have less wiggle room following a Hubble Space Telescope observation that has refined the measurement of the universe's present expansion rate to a precision where the error is smaller than five percent. The new value for the expansion rate, known as the Hubble constant, H0 (after Edwin Hubble who first measured the expansion of the universe nearly a century ago), is 74.2 kilometers per second per megaparsec (error margin of ± 3.6). The results agree closely with an earlier measurement gleaned from Hubble of 72 ± 8 kilometers per second per megaparsec, but are now more than twice as precise.

.......

By bracketing the expansion history of the universe between today and when the universe was approximately 380,000 years old, the astronomers were able to place limits on the nature of the dark energy that is causing the expansion to speed up. The measurement for the far, early universe is derived from fluctuations in the cosmic microwave background, as resolved by NASA's Wilkinson Microwave Anisotropy Probe, WMAP, in 2003.

Their result is consistent with the simplest interpretation of dark energy - that it is mathematically equivalent to Albert Einstein's hypothesized cosmological constant, introduced a century ago to push on the fabric of space and prevent the universe from collapsing under the pull of gravity. Einstein, however, removed the constant once the expansion of the universe was discovered by Edwin Hubble"

 

[aphrodites]

well dark energy is anti matter basicly meaning that its anti everything so nothing escapes and it slowed the expansion of our universe rather than speeding it up

 

[MeteorWayne]

well dark energy is anti matter basicly meaning that its anti everything so nothing escapes and it slowed the expansion of our universe rather than speeding it up

Welcome to Space.com

You've got that thoroughly mangled.

Dark Energy is not matter. It is a placeholder name for a force which IS apparently speeding up the expansion of the Universe at this time. So it's not "anti everything" whatever that means. Everything escapes it.

Dark matter is a placeholder name for one or more types of matter that we currently cannot detect through electromagnetic means either by emission or absorbtion. It appears to interact with normal matter purely through it's gravitational effect. Currently searches and experiments are underway to identify candidate particles which may be able to be detected through subtle effects we haven't figured out, or had sensitive enough instruments for.

On local scales (hundreds of millions of light years) through gravitational effects it slows the local expansion of objects such as galaxies or galaxy clusters.