Are there stars in intergalactic space?

[Sunspace]

@Squink

It’s been a few years, and refs have disappeared. Meanwhile, Wikipedia isn’t so good on false vacuums and inflation.
However, Guth’s 1991 article Can a Man-Made Universe Be Achieved by Quantum Tunneling Without an Intial Singularity, contains the relevent point in its abstract: 10 kilograms is considerably less than all the matter currently in the universe. The rest of the matter/energy that’s around today appears as the false vacuum decays and space expands.

Say what? The universe evolved from an initial mass of only ten kilograms? So the popular representation of all of today’s mass crushed into a fiery point is wrong? (I always wondered why it didn’t get stuck in a black hole…)

[Squink]

@Sunspace

So the popular representation of all of today’s mass crushed into a fiery point is wrong?

Yup.

[Chronos]

I’ve just been reading the bit in the wikipedia link about the Andromeda galaxy and blue shift, and was wondering whether if someone who was observing our galaxy from within Andromeda would see a red or blue shifting galaxy?

If we are both blue shifting relative to each other, does this suggest a future cataclysmic collision? Is it possible that the Andromeda galaxy is moving towards us but because we are moving away it will never catch up to us? How would we be able to determine this?

If they’re Doppler blueshifted relative to us (which they are), then we’re also Doppler blueshifted relative to them. If they were just chasing us through space, at the same speed, then there would be no Doppler shift. Yes, this does mean that we’re currently approaching each other, but it does not necessarily mean that we’re going to collide, any more than you’re going to collide with the cars on the other side of the highway median: It’s more likely that we’ll just pass by each other. And even if we did collide, it wouldn’t be catastrophic: Galaxies are mostly empty space, after all, so the only effect on us would be that the night sky would get prettier.

[CC]

Ok, now I’m more confused than ever. I just went to Google Earth (Sky) and looked at the sky. When I look at Casseopiea, and then go down a bit, I find the Andromeda galaxy. It’s just a tiny smudge, just as it seems when I see it through the binoculars, maybe a bit more clear, even. But tiny. Much smaller than the distance across Casseopiea, for example. It’s not until I zoom in that I see the galaxy as it appears in a lot of pictures, including a link farther up the thread. But it still only takes up a tiny portion of the sky. The moon would definitely block it out. So, how big, really, is the Andromeda galaxy from Earth? If I could see it all, would it actually be the size of 7 moon diameters? Or is it really just that tiny smudge size?

[Chronos]

The only part you can see with your naked eye is the (relatively) bright core, which appears as just a tiny smudge. The whole thing is seven moon diameters across. Note that the moon is a lot smaller in the sky than most people realize: It’s hundreds of moon diameters from one horizon to the other. So seven moon diameters across still represents only a very small portion of the sky, as you noted.

[CC]

Sorry to be so obtuse about this, but I want to have it right. The image that Google Earth uses for M31, the image that shows the galaxy as a spiral when you close in on it, is really misleading, then? If one could really zoom in on that little smudge underneath Casseopiea, one would see that it is, indeed, just the center of the whole, large spiral? And if one could light up the entire galaxy in the sky, that is, if one could make the entire galaxy visible from earth with the naked eye, it would, in fact, be seen as a large spiral, 7 times the diameter of the moon?

[dtilque]

@Chronos

Yes, this does mean that we’re currently approaching each other, but it does not necessarily mean that we’re going to collide, any more than you’re going to collide with the cars on the other side of the highway median: It’s more likely that we’ll just pass by each other.

People who study such things are fairly cerain the two will collide. In my previous post (#50, which you’ve conveniently ignored), I mentioned a recent S&T article about it. It turns out that article is on the web link to pdf:

Astronomers can’t determine the timing of this grand
collision with any precision, but it will almost certainly
happen eventually. The assumption of an eccentric orbit
and head-on collision depends on Andromeda having no
appreciable proper motion, or transverse (sideways) velocity.
If M31 has an appreciable transverse motion, the two
galaxies might miss one another by a few hundred thousand
light-years, but the loss of orbital energy during the
close encounter will make a head-on collision likely during
a second pass a few billion years later.

@Chronos

And even if we did collide, it wouldn’t be catastrophic: Galaxies are mostly empty space, after all, so the only effect on us would be that the night sky would get prettier.

Well it’s potentially catastrophic. But the article goes into what could happen to the Sun so I won’t repeat it here.