Well. This could be a game changer. New Warp Drive theory

[dangerous_safety]

That only holds if superluminal travel allows for arbitrary speed. I would not be surprised if, should superluminal travel be possible, there exists some fundamental constraints on either the maximum and/or minimum velocity. If your superluminal drive can only get to 1.002 c, then its still superluminal, but not in any meaningful way. Similarly, if your superluminal drive can only go at speeds higher than 10^18 c, fine control will be nearly impossible.

[SeanR]

There is also the issue that, even with a radio-shell that is 200LY in diameter by this point, we're still a tiny pinprick in the cosmos. Other radio waves, at least the undirected ones, (which would be most of them, unless we were, for some reason, singled out for an attempt at communication), might very well fall through the noise floor before they ever reach us.

At least, that's how this layman views it.

I do NOT know much about physics, but I wonder if the big bang expansion might be a loophole to causality. That we can't leave our universe but shortcutting to another spot in it, that had the same initial conditions, the same big bang, could be possible. I'll concede probably not.
It is probably a case that I can imagine too easily things that can't exist. Things like anti-gravity metal, accidental teratogens that can render humans into new forms of life, while retaining their intelligence and identity, and radiation that weakens only people from the world it was ejected from after a supernova engulfed it.

[Bear]

The existence of natural "stargates" isn't completely impossible, or at least we haven't proven yet why not, but the odds are on the same order as the odds of all the atoms in your underwear simultaneously quantum-tunneling one meter to the right and arriving in relative locations so precisely matching that they'd still be recognizably your undergarments as they fell to the ground next to you.

Your basic 'primordial black holes' all coming into existence in the few instants following the big bang, could in theory be entangled - could be the mouths of primordial wormholes linked to one another.

Without the continual support of some kind of negative-mass matter, these would be expected to disentangle, collapsing the wormhole, within microseconds. But that expectation is something like a half-life expectation; the entangled state is just as likely to remain intact for that number of microseconds.

Primordial black holes have a strange property that their event horizon cross section is so tiny that they never consume anything. Whatever gets close to them loops around their gravity field but would have to be smaller than an atom and aimed with absolute precision to actually fall in. They could literally pass all the time the universe has had, without taking in a single hydrogen atom. So, maybe, out there in the void, where they're not interacting with much matter, the entanglement collapse gets less likely? Like, a millisecond instead of a few microseconds?

It's a whole lot of milliseconds since the Big Bang. But, in an academic sense, I think it's just barely possible that there might be a couple of primordial wormhole mouths that haven't disentangled yet. But, if so, every letter you've read in this post has been a slice of time during which it's overwhelmingly likely that they DID finally disentangle. And assuming you were to find them, and detect them, before they disentangle, you still have to figure out how you're going to get yourself through that cross section that's less than an atom wide.

In other words don't get your hopes up.

[stevebowers]

In the OA scenario, one reason that there may be long-distance traversable wormholes which would take you to a distant location, perhaps outside the Hubble Volume, is that there may have been a civilisation in the earliest seconds of the universe, which either found or created these wormholes, and stabilised them while they drifted apart because of expansion. These wormholes still exist and are still stable, even though the civilisation that found /created them is long gone. So it isn't impossible to find a Fargate that will take you to a very distant galaxy, but it is impossible for the events in that distant location to interact with our galaxy except through that 'hole.

[stevebowers]

That only holds if superluminal travel allows for arbitrary speed. I would not be surprised if, should superluminal travel be possible, there exists some fundamental constraints on either the maximum and/or minimum velocity. If your superluminal drive can only get to 1.002 c, then its still superluminal, but not in any meaningful way. Similarly, if your superluminal drive can only go at speeds higher than 10^18 c, fine control will be nearly impossible.

Even if the constraint on superluminal travel was that the top speed were 1.002c, that would still be enough to create causal loops in some conceivable sets of frames of reference. Once you have created a closed time-like curve in this fashion, you can use it to send information both backwards and forwards in time, creating paradoxes of various kinds. This would be an undesirable consequence, I think.

[iancampbell]

I am not optimistic about the development of any meaningful superluminal drive.

Partially because I somewhat doubt the physics of negative energy and none of the candidates for types of exotic matter that I've heard about seem likely to be possible for us to design with, build with, contain, and use.

Partially because the speed of light seems to be a fundamental limit on causality - the rate at which any energy can change anything distant from itself.  And I believe in a fairly strong causality.  OA with its notion of wormhole mouths created by entanglement and then moved apart through realspace, with preservation of the Vissier limit on propagation of change, seems (barely) plausible to me.  An out-and-out superluminal drive that can be used to go in any direction does not.

But mostly because of how much more horrible it makes the Fermi Paradox.  I can buy the notion that we're alone in this galaxy, or alone in the nearest 200 galaxies.  We literally don't know how long the odds were.  But if you now introduce a superluminal drive, and aliens at least as smart as us who can use it, we suddenly have to explain why we're alone in countless millions upon millions of galaxies.  

All those places where life could have arisen is one thing without a superluminal drive.  But if there is one, then we have to consider places where life could have arisen anywhere in the universe, because if they have arisen and discovered a superluminal drive we'd have met them by now.

Well, one possibility is that FTL drives cannot be arbitrarily fast. Star Trek, for example, has a definite speed for warp travel. Various instantaneous-jump drives in fiction have proportional errors in destination coordinates, and punishing computation requirements that limit effective travel speed.

Say your FTL drive will let you "travel" at a pseudo-speed of 1000c. That gets you to Alpha Centauri in a few days, but the Andromeda Galaxy takes 2000 years. And the Virgo Cluster takes 40,000.

[Vitto]

I am not optimistic about the development of any meaningful superluminal drive.

Partially because I somewhat doubt the physics of negative energy and none of the candidates for types of exotic matter that I've heard about seem likely to be possible for us to design with, build with, contain, and use.

Partially because the speed of light seems to be a fundamental limit on causality - the rate at which any energy can change anything distant from itself.  And I believe in a fairly strong causality.  OA with its notion of wormhole mouths created by entanglement and then moved apart through realspace, with preservation of the Vissier limit on propagation of change, seems (barely) plausible to me.  An out-and-out superluminal drive that can be used to go in any direction does not.

But mostly because of how much more horrible it makes the Fermi Paradox.  I can buy the notion that we're alone in this galaxy, or alone in the nearest 200 galaxies.  We literally don't know how long the odds were.  But if you now introduce a superluminal drive, and aliens at least as smart as us who can use it, we suddenly have to explain why we're alone in countless millions upon millions of galaxies.  

All those places where life could have arisen is one thing without a superluminal drive.  But if there is one, then we have to consider places where life could have arisen anywhere in the universe, because if they have arisen and discovered a superluminal drive we'd have met them by now.

Well, one possibility is that FTL drives cannot be arbitrarily fast. Star Trek, for example, has a definite speed for warp travel. Various instantaneous-jump drives in fiction have proportional errors in destination coordinates, and punishing computation requirements that limit effective travel speed.

Say your FTL drive will let you "travel" at a pseudo-speed of 1000c. That gets you to Alpha Centauri in a few days, but the Andromeda Galaxy takes 2000 years. And the Virgo Cluster takes 40,000.

Also, I presume, all of the proposed "serious" FTL methods assume that debris aren't a problem. If they are I guess that going FTL is gonna be tricky, to say the least.

[iancampbell]

I am not optimistic about the development of any meaningful superluminal drive.

Partially because I somewhat doubt the physics of negative energy and none of the candidates for types of exotic matter that I've heard about seem likely to be possible for us to design with, build with, contain, and use.

Partially because the speed of light seems to be a fundamental limit on causality - the rate at which any energy can change anything distant from itself.  And I believe in a fairly strong causality.  OA with its notion of wormhole mouths created by entanglement and then moved apart through realspace, with preservation of the Vissier limit on propagation of change, seems (barely) plausible to me.  An out-and-out superluminal drive that can be used to go in any direction does not.

But mostly because of how much more horrible it makes the Fermi Paradox.  I can buy the notion that we're alone in this galaxy, or alone in the nearest 200 galaxies.  We literally don't know how long the odds were.  But if you now introduce a superluminal drive, and aliens at least as smart as us who can use it, we suddenly have to explain why we're alone in countless millions upon millions of galaxies.  

All those places where life could have arisen is one thing without a superluminal drive.  But if there is one, then we have to consider places where life could have arisen anywhere in the universe, because if they have arisen and discovered a superluminal drive we'd have met them by now.

Well, one possibility is that FTL drives cannot be arbitrarily fast. Star Trek, for example, has a definite speed for warp travel. Various instantaneous-jump drives in fiction have proportional errors in destination coordinates, and punishing computation requirements that limit effective travel speed.

Say your FTL drive will let you "travel" at a pseudo-speed of 1000c. That gets you to Alpha Centauri in a few days, but the Andromeda Galaxy takes 2000 years. And the Virgo Cluster takes 40,000.

Also, I presume, all of the proposed "serious" FTL methods assume that debris aren't a problem. If they are I guess that going FTL is gonna be tricky, to say the least.

Well, yes. One thing we are fairly sure of is that travel at FTL speeds in real, unstressed space is impossible. So FTL travel doesn't involve a true velocity. Fictional FTL drives involve either space warps (Startrek), jumps into and back out of some higher dimension (hyperdrive) of which details vary greatly, or instantaneous jumps by some as-yet-unknown (and usually with no attempt to specify) mechanism.

AFAIK the only FTL drives under serious discussion in a semi-serious context involve space warps (Alcubierre/White and this new one) or wormholes, neither of which involve real velocities through space. However, what you call debris is another matter. What happens if your White-drive ship encounters extreme gravity fields such as in the environment of a neutron star or black hole?

[Bear]

FWIW, "debris" is something I think likely to be common enough to shape the future of interstellar travel whether superluminal or not.  

It's a long way between rocks in the Oort cloud (and yes, out there ice is just a kind of rock). I mean, the distance between two house-size rocks that are nearest neighbors to each other might be the distance from here to Neptune.  But the Oort cloud basically goes out to the edge of the sun's Hill Sphere, and there's no indication that interstellar space is much less densely populated.  In fact, regions of interstellar space inside the spiral arms of the Milky Way are likely populated considerably more densely than our Oort cloud.

And we keep finding big things in our Kuiper belt.  Like Sedna and Eris, etc.  Those would be planets if they were close enough to the sun that they'd gone around it enough times to clear their orbits.  I haven't seen any reason to suspect that our Oort cloud doesn't follow the same size distribution.

So, if you point your nose at another star and start moving, you're likely to pass near dozens of interesting rogue worlds along the way.  There may be more rogue worlds than there are proper planets.  And your course may intersect the trajectories of hundreds, or thousands, of little rogue rocks ranging from dust to beach sand to boulder to building size.  

You can try to detect them and destroy them before you hit them.  But there'll always be a few you miss, or a decision about repair budgets vs. energy budgets.  You can try to detect the really big ones and maneuver to miss them. But that'll always cost you reaction mass, and it may be delta-vee you'd really rather have used for something else.  If you wind up significantly off-course you might not be able to reach your destination without more reaction mass.

So if your velocity is too high, in general, then you will need to take on reaction mass, or fuel, or raw material to make repairs, occasionally.  But if your velocity is too high, in general, relative to these rocks and rogue worlds around you, then they're all hazards rather than resources and you can't do that.

So there may be a practical limit to long-range interstellar travel that's considerably less than one one-hundredth of a percent of  light speed, in that if you go faster you start hitting things that do too much damage, or spending too much delta-vee on avoiding them, and can't resupply for the repairs, fuel, and reaction mass it costs you.  

So it would take four thousand years to get to Proxima Centauri, but we can expect to have settled hundreds, or thousands, of mostly-tiny rogue worlds first - as they drift in and out of our Hill Sphere or as we encounter them along the way.  Spreading through the galaxy would happen mostly as the rogue worlds we settle drift apart rather than as we deliberately travel to other stars.

[stevebowers]

Deep space objects are a bit of a distraction when travelling from star to star. To get to an object in the Oort cloud or in deep space, you have to accelerate to something near interstellar speeds, then decelerate to a near standstill with respect to the object - both of which require fuel and propellant. These objects have almost no gravity, so you need to be travelling really slowly to enter orbit, and there's no atmosphere to help with aerobraking.

Once you get to a deep space object you are stuck there, unless you can use local resources to refuel; so that places a size limit on the size of object that you can approach - either the object has enough resources to support you for the foreseeable future, or it has enough material to produce fuel for the next part of the journey. Most of the smaller objects are going to be useless for both purposes.