[happyscrappy]

I agree that knowing is a worthy cause, but never mind getting there we will not even be able to have anything even resembling a conversation if you have to wait hundreds of years for a response.

Edit: Does anyone know the current thinking of the odds that information could be able to travel faster than light, ie a wormhole? As far as I know they are very slim.

[espadrine]

> Does anyone know the current thinking of the odds that information could be able to travel faster than light, ie a wormhole?

An Einstein-Rosen Bridge is purely theoretical, and mostly a way to understand the equation of general relativity better. The equation requires you to set a few parameters that we have no way of determining currently, and that describe the structure of the universe. By setting those parameters just right, we can imagine really strange things, such as time travel or a wormhole.

But even if those parameters allowed a wormhole, having a traversable wormhole requires exotic matter with negative mass, another thing that we have no tangible proof exists.

In other words, general relativity is so general that it allows behaviour that can't exist in the real world. Computing the odds that information could go through a wormhole is like computing the odds that God exists.

[angdis]

Well, if we do detect a signal, we're not going to just transmit "wassup?" and wait for an answer. I think it will be an interesting problem to have a conversation with other beings where the lag time is measured in decades!

[ifdefdebug]

Well galactic communication is one-way: every civilization reaching the tech level needed to participate in it just starts to send out everything they know, never hoping for anyone to reply. Additionally, every participating civilization starts relaying everything they hear from one side to the other side, so civilizations which are mutually out of range can hear from each other.

There is a galactic consent that nobody will ever be able to actually visit each other.

And of course, this is pure science fiction :)

[pavel_lishin]

Why would you wait for a response? When you send a letter, you don't send the line "Greetings from happyscrappy! How are you?" and then wait for them to reply - you go ahead and ask them questions, tell them about yourself, etc., and then wait for a reply. Or don't! Send them a letter once a week, etc.

[ifdefdebug]

Anything contradicting relativity is currently out of the scope of science and not backed by any observation whatsoever, so any travel-faster-than-light theory has exactly the odds granted to it by it's own believers, and zero for everybody else.

[laumars]

Wormholes don't contradict relativity. In fact they were predicted by relativity (or rather a solution to the singularity problem predicted by relativity).

The scientific name for a wormhole is an Einstein-Rosen Bridge - named after Nathan Rosen and, obviously, Albert Einstein who conceived the idea.

There are other suggestions for "faster than light" travel, but FTL is a bit of a misnomer because the concepts of FTL aren't about having a velocity that's greater than c (the speed of light in a vacuum), it's about warping or cutting through the fabric of space in a way that makes the distances shorter. A wormhole is just one theoretical method of jumping those distances via a shortcut.

[octatoan]

IANAP, but isn't the only argument against faster-than-light-travel the fact that it contradicts causality?

[TheOtherHobbes]

I don't see a problem there. The definition of causality is circular anyway. There's no formal mathematical self-consistent proof of causality. It's just sort-of assumed, and then there are back-arguments from relativity that say "Well, that violates something we sort of assume."

The problem is that in science, if you assume things in a naive way ("What goes up must come down." "Planets travel in circles") you're almost certainly wrong - because the details of physical reality are usually counter-intuitive and unexpected.

So what we really know is:

1. Spacetime is a thing. It has bulk properties described by GR. 2. Er - that's it.

We don't know what spacetime is made of, or what you can do with the things it's made of, or what their properties are.

So I'd classify this as "definitely not known due to lack of knowledge" rather than "definitely not proven."

Proposals like Quantum Dynamical Triangulation, Causal Sets, and Loop Quantum Gravity are beginning to ask what spacetime is made of, but they're barely in their infancy.

The one thing they have in common is the idea that there's a network of - something... - and the reality we recognise propagates across the network.

If the elements are discrete - and they almost certainly are, because of the Planck limit - there will be some moment where an element changes state.

How fast does that happen? What's the mechanism? What limits the state changes? (Adjacency? Some other property?)

It's completely mysterious, and I think it's unwise to make definitive statements about it until it stops being a mystery.

[ifdefdebug]

I don't know if it's the only one, but it is one Stephen Baxter's novel Exultant plays brilliantly with: the people in that universe discovered means to travel faster than light, but at a high price: causality was gone - and they had to get over it.