Recent content by kurros

But is that what actually happens in eternal inflation models? I am no expert in them but I don't seem to remember being told about extra dimensions in that context before. What you describe sounds more like some brane-worlds scenario, which is a whole other thing.

It doesn't matter how small it is, it isn't surprising that we exist during the period of time that the universe supports life. Same as how it isn't surprising that we exist on a planet that supports life, despite the great majority of planets (and the rest of space) being inhospitable to life...

Well it's a bit of a hyperbolic thing to say, and a bit of an arbitrary definition of "end". There is no actual end to the universe in that scenario, its just that nothing much is happening once the last black holes evaporate. There will still be cold dead stars and planets floating about, since...

It does in the quantum case though. In the example I gave, there is probably no signal at all, not even one photon. That is literally zero signal, unless you happen to get extremely lucky. So "probably zero signal" is philosophically quite different to "an extremely weak signal" I would say...

Well, again only from a classical perspective. With quantized photons there will eventually be a time when the probability of one photon from an object arriving in the next trillion years will be vanishingly small. A finite number of emitted photons is stretched over infinite future time.

That's not true, is it? Due to the accelerated expansion of the universe, distant objects are moving outside our observable horizon all the time. Unless I am mixing up different cosmological horizons, those can get confusing. I don't think so though. In the far distant future our local group of...

Actually marginalising likelihoods is in general not easy, because you are trying to do a numerical integration in a 3D (in your case, but often higher D) space. But there are a lot of tools out there for doing it, for example you could check out PyMC since you said you are using Python. But...

Actually the first statement is not true, at least not for the reason implied. All Lagrangians in QFT are invariant under spatial rotations since they are Lorentz invariant, but that is separate from their internal symmetries, i.e. gauge structure. SU(2) as an internal symmetry means the...

What? Oh you mean once the mass stops falling? But that wasn't the question here, we were just discussing the falling part. Sure, but it can still be pretty big. It depends on the masses involved. Tidal forces can tear apart stars, so they are not universally small.

So? I'm not sure what your point is. The dark energy isn't sourced by the masses, sure, but so what? Different how? We are just talking about whether geodesics diverge or converge in both cases. I.e. whether things fall towards or away from each other. No reason to think the situation re...

Not if consider the whole system. When you drop something in the Earth's gravitational field, the Earth also falls *up* towards the object. Both are in free fall towards each other, with identical acceleration. So their geodesics are converging. Put it this way. Attach masses to your massless...

Aside from Peter's technicality I would say that's the gist of it, yes.

I don't think so. The vacuum energy accelarates things "for free", but you need mass in the right place to get some energy. Like on Earth, really. Gravity accelerates things for free, but you need to find something high up in the gravitational potential that you can let fall to extract energy...

It's a logical definition if you look back historically and see that the Big Bang model arose long before the idea of inflation.

The potential shape comes from dark energy, it has nothing to do with the positions of the galaxies. All the motion will work out the same if you arbitrary translate the potential. Or perhaps you have to boost it too so that the centre stays comoving. I'm not so sure though, the original...