The universe is disappearing!
Well, from our perspective anyway. It seems that someone has done calculations recently to show that not only is the universe expanding, but it's accelerating its expansion such that portions will gradually become beyond our visual and radio reach by moving at or beyond the speed of light as seen from Earth, leaving us cosmically isolated with only our immediate neighbors within a few billion years.
Unfortunately, it seems this study has not yet reached the printing presses of publication, so I wasn't able to look at the math (it's a subscription-only journal until the article is a few months old anyway), and don't have the time to work through it myself at the moment. Consider that a challenge to work out some provisional numbers to see how/what/when things could be expanding beyond the speed of light as seen from earth. Is it just things on the opposite side of the universe, our side, or all of it? Which things will we lose first? Are any of the more notable stars/clusters/constellations/objects on the list for the (cosmically) near future?
The article also talks about a "frozen" ghost image left as things blip out, but I couldn't tell if this means we just see an unchanging image for a brief time before nothingness, or if the ghost images remain somehow, but are just never updated. I don't have quite enough grasp of the things involved to work that portion out - anybody have some insight?
Regardless, it's all some pretty weird stuff - the idea that portions of the universe that we can see now and have used to prove very fundamental portions of the physics governing things will no longer be within reach later is a bit disconcerting. Some portions are already beyond the event horizon, and who knows what information we may have missed by not having those data points? So, SETI@Home contributors, you may want to fire up a few more dual-cores, because your time is (sort of) limited. :P
Read the full story on Space.com, and a related article with some extra details.
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Cool stuff - thanks guys!
Cool stuff - thanks guys! I've known about the universe expanding, and how we use red shift and gravitational lensing to make measurements of it, but the possibility of exceeding the speed of light is what caught my eye. Looks like I'll have to do some reading about Hubble's law as well. Thanks Henrik for finding the pre-publication PDF too!
[...] Tony, It has long been
[...] Tony, It has long been known that the Universe is expanding. The rate at which it expands and whether it accelerates or decelerates will depend on a range of cosmological constants. We don’t know whether these are truely constant or change over time. There are various ways of measuring these constants, which generally include taking the redshift of distant objects and using a series of ‘standard candles‘ to measure the distances or with gravitational lensing. [...]
Hi Tony, I don't know how
Hi Tony,
I don't know how much physics you know, so apologies if the following is obvious to you.
This effect has been expected for a long time. Cosmological redshift occurs because space itself is expanding, and so the distance between galaxies is increasing by a given rate. If this rate exceeds the speed of light, then light from such a galaxy could never reach us.
For a simple calculation, you can use Hubble's Law, v= HD. This states that the velocity at which a galaxy is seen to be moving away from us (v) is equal to its distance from us (D) multiplied by Hubble's constant (H). Hubble's constant is about 72 km/sec/Megaparsec. If we let the velocity be the speed of light, we get a distance of about 13.8 billion lightyears, so objects which are more than this distance away should be invisible right now. There are complicating factors, so this doesn't really hold true - the Universe is estimated to be about this age, so no objects should currently be more than 13.8 billion ly from us. Also, the value of the Hubble constant is thought to be changing (the acceleration you mentioned).
Because cosmological expansion is per unit distance in space, the first objects to disappear from our view will be those furthest from us. The effect is very small for relatively nearby objects, so they will stay in sight for a very long time.
Most of the notable stars, clusters and constellations that we know of are within our own galaxy or occasionally in a nearby galaxy (the Large and Small Magellanic Clouds and the Andromeda Galaxy, for example). These galaxies are bound together by gravity into what is called the 'Local Group'. Andromeda is actually heading on a collision course with out own galaxy! These galaxies are likely to remain bound together by gravity despite the cosmological expansion, so should always be visible. Clusters of interesting galaxies further afield will be lost from view eventually, however.
As for the 'frozen images', I think it means that we won't be able to collect new information after a certain point. For a galaxy which is a million lightyears away, the light from an event which happens now will take a million years to get to us. If the galaxy crossed the 'horizon' right now, we would get another million years' worth of light and then it would disappear. We would be able to collect no information about future events in that galaxy.
Hope this makes sense, and that I haven't made too many errors.
I can recommend 'The Last Three Minutes' by Paul Davies as a good book on possible endings for the Universe:
http://tinyurl.com/37bs6b