# The stars are going out! (a question about vacuum metastability)

So I had an idea earlier today and was wondering. Most sources you consult about the supposed "vacuum metastability event" say that the bubble would begin expanding at NEARLY the speed of light, not exactly the speed of light. How much slower would it really be? Would it give us enough time to see it coming or would it still happen so fast we'd be annihilated instantly?

For example, if it was slowed to 99%, 98%, 97% etc., would we be able to see the stars going out in the night sky like so many popular sci fi flicks? How long could we ever have to conceivably prepare for a vacuum metastability event before it arrives? Days? Months? Years?

• The only thing i could find in the literature says the bubble expands at "essentially" the speed of light. So I'm guessing it's instant for all intents and purposes. – ApproachingDarknessFish Jul 1 '16 at 21:07
• In the novel Manifold:Time, the metastable vacuum is breached and a "true" vacuum created, expanding at the speed of light. Beyond .9 c , things are going to arrive essentially behind their own light come, so you will never see it coming, or have so little time to react it is essentially instantaneous. – Thucydides Jul 1 '16 at 21:29
• @Thucydides if we see Andromeda going out with a bubble of extinction moving at .999c, for most geometries it will be centuries before it reaches Earth. Andromeda is the nearest big galaxy! The end would be nigh in cosmic terns but not in human terms. – nigel222 Jul 2 '16 at 11:36

Wikipedia's section on vacuum metastability events provides a link to a paper on this, Gravitational effects on and of vacuum delay. From the introduction of this paper:

This [decay] is a quantum tunneling event, and has a certain probability of occurrence per unit time per unit volume, $\Gamma / V$. Once the bubble materializes, it expands with a speed asymptotically approaching that of light, converting false vacuum into true as it grows.

Thus it does not have a fixed speed, but rather grows faster and faster, asymptotically approaching the speed of light.

It is not just a function of speed, but also distance. The speed of light is not very fast in relation to the size of the universe. At present, the most distant observable object from Earth is a galaxy called UDFj-39546284. It is 13.2 billion light years away. So if the vacuum metastability event happened there, we would have 13.2 billion years to prepare.

Here lies a problem. Using the Hubble telescope, we can see UDFj-39546284 as it was 13.2 billion years ago, but not as it is now. UDFj-39546284 could have already been eaten by the vacuum metastability event and we would not know. The edge of the event could literally be 5 feet away from you and you would have no way of knowing. Everything we see happens in the past. If the Sun were to instantly go out, we would not know for 8 minutes and 20 seconds, as all the light and gravity emitted from the Sun takes that long to reach Earth. An easier way of putting it, is that the instant we saw the lights stop shining from a distant source, we would be destroyed.

• Not quite. Scientists are very cagey about exact claims - for example whether a particle has zero mass or not - and will usually state it is bounded and no more than some tiny amount, rather than asserting it is precisely zero. Same here - suppose the correct physics model would show the bubble expands at (1- 10^-30).c, even so for a galaxy a few billion lightyears away the difference might mean you could in theory notice something before annihilation. – Stilez Jul 2 '16 at 13:30
• The problem is that speed is relative. C is the only thing it could be without a preferred reference frame. We're talking about munging spacetime itself, so how can the speed be something relative to matter in some particular reference frame? – JDługosz Jul 2 '16 at 15:35
• Disclaimer - I don't know the maths, but the point is nobody is certain of it (edge cases proved Einstein over Newton, maybe edge cases will prove current theories aren't exact too). Point being, how certain is it that the structural effect of a change to spacetime (if we can call it that) would propagate at exactly c through spacetime? It sounds like it should..... but I think it would be a brave person who said "what else could it be". That thinking's been wrong more than once. – Stilez Jul 2 '16 at 20:59