I’m thinking of something imaginary that would cause everything but our galaxy to blink out of existence in an instant. Would we be aware of such an event in our lifetime or wouldn’t we know anything was wrong for maybe millions of years? In other words might it have already happened?
What’s the speed of light? Where is Alpha Centauri?
The nearest objects outside our galaxy are the Magellanic Clouds, which are 160,000 and 200,000 light years away. So if everything outside our galaxy disappeared, we would not notice anything for 160,000 years.
A few light years away. It’s the closest star in our galaxy.
Nitpick – Alpha Centauri is the third closest star. The closest is the Sun, and the second closest is Proxima Centauri, a small star not visible to the naked eye that orbits Alpha Centauri.
ETA: I just realised a grammatical ambiguity there: it’s the star that orbits Alpha Centauri, not the naked eye.
Double nitpick, Alpha Centauri is a binary system comprised of Alpha Centauri A and B, around which Proxima Centauri orbits.
Fine, so it’s Alpha Centauri C if you want to be picky. And it is the closest star to the Sol system.
Unless it happened 159,999 years, 11 months, 364 days ago. Then we’ll find out tomorrow! :eek:
Which raises the point that “when something happens” is a slippery concept at interstellar, much less intergalactic, scales.
Search is fighting me just now, but I recall a recent thread about the expected consequences for Earth of the rest of the Milky Way galaxy disappearing. The informed concensus was it wouldn’t matter spit.
Losing the entire rest of the universe would be a far smaller impact, so far as the physics we know, than would be losing the rest of the Milky Way. At least on anything like even geological or solar timescales. It certainly won’t matter at all on individual human, or even collective humanity’s, timescales.
there was a similar thread back in march
mc
Unless we went to the edge of our galaxy first and said "Hey… who turned out the stars? "
I was gonna say “But helixes, guys, helixes!” But thought it would be too obscure, and possibly breaking the “don’t be a jerk” rule…
Last I heard, there was actually some dispute about whether Proxima was gravitationally bound to the alpha Cen system or not. It might just happen to be passing by.
In any event, all three of those stars are certainly part of the Galaxy, as is every other star individually visible to the naked eye.
A recent paper confirms that Proxima is bound to the Alpha C system. So saying Rigil Kentaurus (a traditional name which is now the official name of Alpha C) is the closest star system is correct. Singling out Proxima for being closest is being a bit pedantic.
The Magellanic Clouds are arguably part of the Milky Way. They’re in orbit (probably) around our galaxy and are being torn apart by gravitaional interactions. They’ll eventually be absorbed. So by that logic, we won’t know about the rest of the Universe disappearing for about 2.5 million years when the Andromeda Galaxy blinks out.
By chance I just happened to watch this show recently: http://topdocumentaryfilms.com/everything-and-nothing/
Though I’t doesn’t address you question directly it provides a deep insight to how everything works and is interconnected. Extremely fascinating. I got it on demand somehow (hulu? Amazon Prime?), I highly recommend it.
.
What’s the orbital period of [del]my naked eye[/del] Proxima Centauri around Alpha? Presumably if it’s in orbit, it’s not always the closest star to us (unless the plane of orbit was exactly perpendicular to our line of view)
If the plane of orbit were exactly perpendicular to our line of view, it’d never be the closest.
And the period of 550,000 years is in the first paragraph of that Wikipedia link. On that kind of time scale, you’ve got to worry about not only Proxima’s motion, but also the motion of other stars in our vicinity. There are a lot of red dwarfs out there that are on their own, and occasionally one of them will wander close to the Sun.
The Andromeda Galaxy wouldn’t “blink out” but fade away over tens of thousands of years, from the nearest stars to the furtherest ones. It would be like see in an MRI of a galaxy.
I hope there’s other arguments … because the logic you give could also be applied to Andromeda … we are on collision course right now …
Generally, the Magellanic Clouds are considered separate galaxies … here’s a picture of Andromeda showing her two dwarf galaxies … these two are normally catalogued as separate galaxies … certainly in the future they will be incorporated into the mother galaxy, but until then they really are separate structures …
I suppose we could reclassify them and demote them as something other than galaxies … like we demoted Pluto … and probably get by with that easier, those in the Northern Hemisphere may not even be aware of the existence of the Magellanic Clouds …
Come to think of it, we need to define “blinking out”. Does only the matter itself disappear, or does all of the light outside of our Galaxy vanish, too? If we’re just talking about someone overwriting those parts of the simulation with all zeroes, then the latter seems more plausible to me.
I also highly recommend this. It explains things I’ve often wondered about, in terms that a non-physicist like me can understand.