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zerocold
2008-Apr-23, 05:32 AM
Someone has tested it? there is experimental data of the universe's space expansion?, something like sending a radio signal to one place (maybe to another planet) and check if there is a doppler effect?

I mean, a controlable experiment, not only checking the stars

Grashtel
2008-Apr-23, 12:05 PM
Someone has tested it? there is experimental data of the universe's space expansion?, something like sending a radio signal to one place (maybe to another planet) and check if there is a doppler effect?

I mean, a controlable experiment, not only checking the stars
No because at short distances (in cosmological terms, ie millions of light years) other forces overwhelm the expansion so its impossible to test it.

Hornblower
2008-Apr-23, 12:12 PM
Someone has tested it? there is experimental data of the universe's space expansion?, something like sending a radio signal to one place (maybe to another planet) and check if there is a doppler effect?

I mean, a controlable experiment, not only checking the stars
We have gone out only a few billion miles with radar and two-way spacecraft telemetry. That gives us the distances and radial velocities of the objects in question, among other things. Whether or not the effects, if any, of cosmic scale space expansion are measurable with today's technology, I do not know.

Edit: Grashtel answered my question as I was writing it.

speedfreek
2008-Apr-23, 06:21 PM
The rate of expansion is estimated to be around 70 km/s per 3,262,000 light years. This equates to 7 millimeters a second per 3.2 light years, but unfortunately the expansion only happens in the voids outside of galactic clusters, so there is no point testing how the distance to Proxima Centauri (the Suns nearest neighbour) increases. Galaxies are held together by gravity, which also causes galaxies to cluster together into groups. The expansion only happens between places that are not bound by gravity.

hhEb09'1
2008-Apr-23, 06:29 PM
The rate of expansion is estimated to be around 70 km/s per 3,262,000 light years. This equates to 7 millimeters a second per 3.2 light years, accepting your first value, wouldn't the second value be 70 millimeters a second per 3.2 lightyears?

Amber Robot
2008-Apr-23, 06:46 PM
I mean, a controlable experiment, not only checking the stars

Exceedingly little of astronomy is done with controlled experimentation. If you are waiting for that, you'll be waiting a long time.

The universe is the experiment. Astronomers are trying to interpret the results.

Think of astronomy more like archeology.

mugaliens
2008-Apr-23, 06:48 PM
The expansion only happens between places that are not bound by gravity.

Expansion happens everywhere. It's just that locally (within the confines of a galaxy) it's hidden by the far greater effects of gravitational attraction.

speedfreek
2008-Apr-23, 09:48 PM
accepting your first value, wouldn't the second value be 70 millimeters a second per 3.2 lightyears?

Oops, yes you are correct. :doh:

I hate those pesky decimal points!

(At these scales, it makes no difference to the overall message my post conveyed, just for the record!)

speedfreek
2008-Apr-23, 09:55 PM
Expansion happens everywhere. It's just that locally (within the confines of a galaxy) it's hidden by the far greater effects of gravitational attraction.

There are different points of view on this one, it depends on how you define expansion.

If expansion is defined as the increase in measurable distance between objects, then my description is fine.

If expansion is defined as something that imbues space with a repulsive force that gravity resists, then yours is fine.

Perhaps I should have said measurable expansion, eh? :)

Argos
2008-Apr-24, 12:55 PM
More clarity on titles, folks, please:

Universal expansion: someone has tested it? [has someone tested it? - whatever]

Yes. Someone has tested it. It is a perfectly valid empirical evidence to our best knowledge, not a conjecture.

Neverfly
2008-Apr-24, 01:05 PM
More clarity on titles, folks, please:

Universal expansion: someone has tested it? [has someone tested it? - whatever]

Yes. Someone has tested it. It is a perfectly valid empirical evidence to our best knowledge, not a conjecture.

It's a bit of a trick question in any sense- Although it has been tested and is being tested still, it has not been Directly Tested as mentioned in some posts above.

I look at it a bit like.. For example: Testing a piece of steel to see if it's up to strength standards. It's tested but not directly tested by say- taking a hammer to the thing and whacking on it 'til it gives.

matt.o
2008-Apr-24, 10:57 PM
If I recall correctly, future high resolution spectroscopy may be able to track the change in redshift of distant objects over the course of several decades. I can dig up a link to a paper if anyone requires it.

parejkoj
2008-Apr-25, 03:23 AM
matt.o is correct. I've linked to this before (http://www.bautforum.com/1050318-post8.html), but it will be quite a few years before the instrument is built, let alone the telescope that it would be mounted on!