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sithum
2010-Apr-07, 01:19 AM
I was wondering what percentage of the universe is unobservable with our current level of technology.

What are the main factors that contribute to this "unobservability"?

Is it possible that if there is a star at position (x,y,z,t) in the universe and it is moving at 99.9999% the speed of light relative to an earth observer that it will be red-shifted to the point of undetectability? How many positions/objects (that is invisible positions/objects) like this exist in the universe? (has anyone ever made a guess?). Is there anyway of using a probability formula to estimate the positions of these invisible objects?

astromark
2010-Apr-07, 01:45 AM
Just attempting to clear what you understand about the observable and un observable Universe.
We see and have knowledge of all that is within a 13.7 billion ly distance from here... Not without mentioning all that we do not have knowledge of ie; Dark mater and Dark Energy. If there is more universe beyond that,. If there is we can not know...
Because of the expansion of the space between us, we can not see or know of it. We can make assumptions of matter so far away and accelerated to be outside of our envelope of knowledge... Its not right to think in fractions of the whole. As we have no idea of the whole.
It would seem to be beyond us. In this case 'Us' is the ability to know of and gain intelligence about. At some point the age of and expansion rate defeat our ability to see.

WayneFrancis
2010-Apr-07, 02:24 AM
To expand upon astromark's great comment.

We don't know if the universe is finite or infinite. What we know is that at the large scale it appears flat so if it is finite and unbounded then it is, most likely, many orders of magnitude larger then the observable universe. If the universe is infinite then the question does not produce a viable answer as you can't get a result by dividing something by infinity.

as for the red shift question a velocity of 99.9999%c doesn't produce red shift much higher then the CMBR and we detect that just fine. To the absolute limit I'm not sure. I think the bigger issue is that we can't detect things with a higher red shift then the CMBR because it would get lost in the CMBR. Maybe one of the actual scientists can pipe in on the technical limitation in regards to lower limit of photon frequencies that we can detect.

Jeff Root
2010-Apr-07, 02:38 AM
The total size of the Universe is completely unknown. The best evidence
is that it is much, much larger than what we can see, though it is possible
that it could be somewhat smaller than what we can see (with what appear
to be different galaxies in different directions actually being one galaxy
whose light has reached us by different routes). It is also possible that
the Universe is infinite in extent.

I personally infer that, even if the Universe is infinite, the part of the
Universe which is involved with the Big Bang and the cosmic expansion
cannot be infinite, because of limitations set by causality. If the entire
Universe is involved in the Big Bang and cosmic expansion, then the
entire Universe must be finite. But we don't have evidence one way
or the other.

The current limitations on our ability to see the most distant things are
the faintness of light coming from very distant stars, and the opacity
of the gas which filled the Universe prior to the moment of decoupling
between matter and light, when the cosmic background radiation was
freed to start travelling forever through space. Bigger, better telescopes
allow us to see fainter galaxies. Probably nothing will allow us to see
through the fog of the early Universe, but neutrino telescopes or
gravitational wave detectors are two possibilities that people are
working on.

The redshift of the light from the most "distant" thing we can see --
the gas which emitted the cosmic background radiation -- is Z=1089,
meaning that the wavelength of the light we observe is approximately
1089 times the wavelength of the light as it was emitted.

Your last paragraph regarding positions/objects and probability makes
no sense to me. I don't know what you were trying to ask.

-- Jeff, in Minneapolis

noncryptic
2010-Apr-07, 12:46 PM
We see and have knowledge of all that is within a 13.7 billion ly distance from here

More accurately: we have knowledge of all that is within 13.7 billion years look-back time (except for the dark age (http://arxiv.org/ftp/astro-ph/papers/0307/0307396.pdf)),
which corresponds to a distance of about 45 billion lightyears. http://en.wikipedia.org/wiki/Universe

Afaik consensus has it that the observable universe is only a small fraction of the universe, but nobody has a clue as to how small.

cosmocrazy
2010-Apr-07, 01:17 PM
I don't think anything outside the observable universe has of much consequence to us, if information cannot be sent FTL.

Cougar
2010-Apr-07, 01:38 PM
I was wondering what percentage of the universe is unobservable with our current level of technology.
What are the main factors that contribute to this "unobservability"?

Even for the so-called "visible universe," a not insignificant percentage of our total view is blocked by our own galaxy. Of course, if we wait 100-150 million years, we'll be on the other side of the galaxy and be able to see what we now cannot, but then we won't be able to see some percentage of what we now can.

As previously mentioned, we don't know how big the entire universe is. Initial calculations consistent with cosmic inflation suggest it is a lot bigger than our "visible" patch...

"...the entire universe is expected to be at least 1023 times larger than the observed universe! ...if the inflationary theory is correct, then the observed universe is only a minute speck in a universe that is many orders of magnitude larger." - Alan Guth

If this is correct, the answer to your question would be an extremely small percentage.

sithum
2010-Apr-07, 02:58 PM
...Your last paragraph regarding positions/objects and probability makes
no sense to me. I don't know what you were trying to ask.

-- Jeff, in Minneapolis

Ok, I was asking "if" indeed there exists a part of the universe that is unobservable for any reason: is there a chart somewhere or perhaps a formula that correlates 'seemingly empty regions of space' with 'the probability of there being something there that we cannot see'. I'm not sure how this would be calculated. Maybe looking at redshifts or orbital patterns of nearby objects?

(btw thanks for the info everyone!)

speedfreek
2010-Apr-07, 09:47 PM
I think what you want to know is if we think there is other stuff we should be able to see, given good enough technology?

sithum
2010-Apr-07, 11:17 PM
I think what you want to know is if we think there is other stuff we should be able to see, given good enough technology?

That certainly is one spinoff from my original question.

But I'd like to know more generally if there is a formula or a chart that gives us a probability of there being an object in a certain region of space (obviously for all known objects in the universe the corresponding probabilities will be 1 for all points of space occupied by that object) but is there a formula / chart that gives a probability that a certain region of space is occupied or empty? something to the effect P(x,y,z,t) = p where 0<= p <= 1 (I guess the bounds on (x,y,z,t) would be the known universe boundaries [which I think astromark mentioned in a reply already] along with the age of the universe for t). If we haven't observed an object in a particular region of space at a given time (say a point (x1,y1,z1,t1)) then p would be between 0<=p<1 (i.e. we could make a guess based on 'other factors' to determine the likelihood of there being an object in this particular region of space at this particular time [but it wouldn't be 1 until it was observed]).

Jeff Root
2010-Apr-08, 12:23 AM
sithum,

I'm wildly guessing that what you have in mind is something like the prediction
of the planet Neptune from observed anomalies in the orbit of Uranus, but on
the scale of the entire observed Universe. Is that correct?

-- Jeff, in Minneapolis

Jeff Root
2010-Apr-08, 12:52 AM
Alternatively, you may be thinking that stars and galaxies have a
distribution which should follow some kind of statistical pattern, so
that deviations from the pattern in the form of a deficit of objects
would lead one to suspect that something should be located in
places where nothing is seen.

Is that it?

(If you say "yes" to both, I'm going to be quite discombobulated,
since the two possibilities are utterly unrelated.)

-- Jeff, in Minneapolis

astromark
2010-Apr-08, 12:55 AM
At this point I can only plead with you to except the 'generality' of what you ask... Yes you could draw a graph... Us astronomers love graphs.

'They' pointed the Hubble telescope at an area of space previously uncharted... and tracked that 4mm point for over 100 hours. I trust you have seen the resultant image. I will except that details of my knowledge of that image size might be...off. No mater as the resultant image was spectacular... from this you can make extrapolation's... ( there's a cure for them.):) Those images are not showing empty areas... it looks like the more we look, the more we find. We have not yet concluded the whole sky is like this... but, have zero information that it is not... We just do not yet know.

I wounder if 'discombobulated' is like 'extrapolations' can I be medicated... ?

sithum
2010-Apr-08, 01:02 AM
sithum,

I'm wildly guessing that what you have in mind is something like the prediction
of the planet Neptune from observed anomalies in the orbit of Uranus, but on
the scale of the entire observed Universe. Is that correct?

-- Jeff, in Minneapolis

Such a technique could definitely be used to help determine a value for p, as could your other suggestion. :)