InterGalacticTravel

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:One problem is the TCP timeout.
/*
* [...] Note that 120 sec is defined in the protocol as the maximum
* possible RTT. I guess we'll have to use something other than TCP
* to talk to the University of Mars.
* PAWS allows us longer timeouts and large windows, so once implemented
* ftp to mars will work nicely.
*/
(from /usr/src/linux/net/inet/tcp.c, concerning round-trip time)

OP Pallando asks: Is it possible? What would it take to, say, send something to a neighbour that could land on planets and send back an "arrived safely" message.

The closest candidate is the [Canis Major Dwarf Galaxy], 2.4 x 10^20 meters away. It contains 10^9 stars and is travelling towards us at 2.4 x 10^5 meters per second.

Suppose we wanted to send a solar system out to visit. If we can accelerate our emissary up to about 2.5 % of the speed of light (7.5 x 10^5 ms-1), the trip time will be only about 1 million years. The lightest main sequence star is 1.6 x 10^29 kg, which can burn for 10^12 years, so there is no upper limit to our trip time, beyond how long we think our species will want to wait around to get the message.

Could such an emissary be sent? We could wait around for a [hypervelocity star] and hope it is heading the way we want, but the odds of such a wanderer naturally intersecting a nearby galaxy are not high. Let's come back to that.

Making your own emissary from scratch

Let's assume a high capability civilisation trying to create the emissary. There are 10^11 stars in our galaxy (the milky way). If we dedicated 1% of them to the project, each one would need to contribute 1.6 x 10^20 kg. That's a bit less than the asteroid Ceres. Doable. If we can only get 10^7 helpers, each would need to send a chunk of mass the size of Earth's moon. If we could send a planet the size of Jupiter, it would only take 100 helpers. Which may not be that bad. If you can space the contributions out (say to orbit around a black hole to create a binary system), then if you've got 100,000 years and 1000 helpers, each one would only need to use 1000 solar powers linear accelerators spread through out the asteroid belt, each one sending a 50 ton payload every second.

Altering the orbit of an existing solar system

Let's go back and look at the hypervelocity star option. They theorise that these are formed by a binary system being destabilised by a black hole. So if we want to manafacture one we have two options. A) Push the stars, or B) push the black hole. Each has its pros and cons. For option A, the stars are lighter and therefore easier to push, but they are harder to hit. I like option B. Look around for a stable binary system that is due to be visited by an existing wandering black hole in 10,000 years or so. Work out how much you need to alter the black hole's trajectory to disturb the binary system in precisely the right manner to shoot out one of the two stars in the correct direction to visit your desired galaxy. Crash that much mass into the black hole in advance and Bob's your uncle.

What I like about this option is that it uses finesse rather than brute force. Theoretically it might only take a small nudge, long enough in advance, to make a critical change. Suppose the two binary stars are 10^10 meters apart and the black hole is 10^16 meters away and headed in more or less the right direction. A change of 0.01 meters per second in the black hole's velocity would be enough to any course correction desired. If that feasible? To change the velocity of a mass of 10^31 kg by that amount would need a colision with a mass a million times smaller going a million times faster. So for example, if we could send interstellar mass packets at 10,000 meters per second, we'd need to hit the black hole with 10^25 kg worth of mass. If we could accelerate them up to 30% the speed of light (10^8 meters per second) we need to send just one mass the size of the moon. Not so promising.

Interstellar Bar Billiards

Here's where it gets fun. Because, just like we can use an existing star rather than manufacture one, we could also use an existing [Eccentric Planet] rather than create our own. If we find an existing jupiter-like mass and alter its path to hit the black hole, it will already have enough momentum to make that 0.01 meter per second change in the black hole.

And how to alter the course of such an eccentric planet? Why, hit it early with a much smaller mass, say a wandering Ceres-like mass from the Kuiper belt. And to do that, we could hit the Ceres-like mass with a small asteroid. And small asteroids, according to Nasa, we could move now, with our current levels of technology (abeit with time, funding and resources).

So, you heard it here first. Mankind, with their current technology + a bit of luck and searching out likely candidates via astronomy + a lot of patience, could send a visitor to another Galaxy. Any candidates?

SeeAlso: [Interview with the astronomer who discovered galactic exile stars.]

Tie in with: DouglasReay/DysonBubble

DR's latest conundrum is a bit less ambitious. Supposing that, instead of travelling to another galaxy, we just wanted to send out a message. Perhaps to give the estimated time of arrival of our emissary. Perhaps just to say "Intelligent live woz ere".

My initial thought was to use a sequence of [supernovas]. These could be triggered by using an aimed hypervelocity star to ignite a subcritical mass. If you set off three, A, B and C, and the ratio of A-B : A-C is Pi to 8 decimal places, that should be a clear sign. If you then want a longer message, a fourth supernova D, where the ratio A-B : A-D could use a binary encoding.

However, if you wanted your message to be readable from all surrounding directions, would you need to do anything additional to establish the intended frame of reference? Would you need a fifth supernova, E, where E-B (in your intended reference frame) is exactly the same as A-B? Would that be enough?

However, then I thought of quasars. Normal quasars are limited to one per galaxy, however there are these neat things called [microquasars] which only require a few solar masses. These send out aimed beams of radiation and matter travelling so close to the speed of light that relativistic dilation slows down time by a factor of 100, making a 25,000 light year trip take 250 subjective years (if a passanger could survive in such a ferocious beam).

So that's the carrier wave, but how could one modulate a signal on it? Suppose you could put a [Dyson Bubble] around the solar system? Statites probably wouldn't survive in the direct beam, but by directing the reflection of solar light pressure at the swathe of matter being accreated, they might be able to modulate the timing of bursts, or by exchanging beams of charged particles to set up electromagnetic fields, they might be able to bend the beam slightly, make it oscillate from side to side in a noticable fashion.

If the internet could be extended to other galaxies, would IP6 still be large enough?

: One problem is the TCP timeout.

    /*
    * [...] Note that 120 sec is defined in the protocol as the maximum
    * possible RTT. I guess we'll have to use something other than TCP
    * to talk to the University of Mars.
    * PAWS allows us longer timeouts and large windows, so once implemented
    * ftp to mars will work nicely.
    */
 (from /usr/src/linux/net/inet/tcp.c, concerning round-trip time)

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