Aliens probably long dead, say scientists
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littlebabyjesus
one of Maxwell's demons
Yeah, they normally do nod to these things. At the very least they have some kind of anti-physics button or something.
DotCommunist
So many particulars. So many questions.
here we go, the alby whatsit drive. Not just a star trek idea
Alcubierre drive - Wikipedia, the free encyclopedia
Alcubierre drive - Wikipedia, the free encyclopedia
littlebabyjesus
one of Maxwell's demons
that'll do, tbf. Without it, Star Trek would have been difficult to make.
But it does seem that it partly was a star trek idea.
NoXion
Craicy the Squirrel
The dirty little secret of FTL that most science fiction writers studiously ignore (if they're even fully aware of it in the first place) is that the unity of spacetime in relativity means that FTL travel = time travel.
Here's an explanation to illustrate the point.
Atomic Rockets is a great website for this sort of subject:
If I'm understanding how it works it correctly, the way to use your FTL starship as a time machine is to make your way at FTL speeds to say, Alpha Centauri, and then travel at sublight velocities in the direction directly away from Sol. When you then return to Sol at superluminal speeds, you will have travelled back to a point in time a number of years equal to the distance in light years you travelled sublight away from Alpha Centauri.
So if you want to get back before you first leave, take a little detour.
Here's an explanation to illustrate the point.
Atomic Rockets is a great website for this sort of subject:
Atomic Rockets said:However, very few SF novels deal with the second problem. The aphorism at rec.arts.sf.written goes "Causality, Relativity, FTL travel: chose any two."
Your average physicist holds Relativity quite strongly. It has been tested again and again with an accuracy of many decimal places. They hold onto Causality even tighter. Without Causality the entire structure of physics crumbles. Causes must preceed effects, or it becomes impossible to make predictions. If it is impossible to make predictions, it would be best to give up physics for a more profitable line of work.
Therefore, they chose to jettison FTL travel.
Please note that as far as Causality is concerned, FTL communication is every bit as bad as FTL travel.
Why only two?
Relativity proves that FTL travel is identical to Time travel.
Time travel makes Causality impossible, since it can be used to create paradoxes.
∴ Causality, Relativity, FTL travel: chose any two.
- So if you have Relativity and FTL, Causality is impossible
- If you do not have Relativity, then FTL is not Time travel, so you can have Causality.
- Or more mundanely you can have Relativity and Causality, but no FTL/Time travel
Physicist Stephen Hawking calls #3 the chronology protection conjecture. To help your research, the technical term for time travel is "Closed timelike curve".
Clever readers will have already spotted a possible loop-hole. What if there was some law of physics that prevented Time travel from creating paradoxes? In that case, FTL/Time Travel would not make Causality impossible.
The classic Time-travel paradox is the so-called "Grandfather paradox" (though it actually should be called the "Grandmother paradox"). Boris Badenov sneaks into Mr. Peabody's Wayback Machine (actually the WABAC machine, but who cares?) and travels back in time to when Boris' grandfather was a baby. Boris then gives his infant grandfather a lit stick of dynamite then cackles evilly as his grandfather is blown to bits. Bah-hah-hah!
But wait! Boris' grandfather is now smithereens, he'll never grow up, beget Boris' father, who will beget Boris. In other words, Boris will never exist.
But if Boris never exists, then he will never travel back in time to assassinate his grandfather. In which case grandpop will beget Poppa Boris, who will beget Boris. Who will then proceed to assasinate his grandfather. Start back at the beginning and repeat.
Does Boris' grandfather get blown up? Both Yes and No! A paradox.
Hinson shows there are four ways of enforcing a "no-paradox" rule for time travel. Parallel Universes, Consistency Protection, Restricted Space-Time Areas, and Special Frames. In some ways Special Frames is the best, though it directly contradicts part of Relativity (the first postulate of special relativity is that there are no special frames, "no privileged inertial frames of reference"). Oh well. For details, you'd best read the Hinson article.
The latter three are examples of the Novikov self-consistency principle.
In some late-breaking news, physicists Daniel Greenberger and Karl Svozil have shown that the laws of quantum mechanics enforces Consistency Protection. You can read their paper here, but it makes my brain hurt. Translated into English, they maintain that time travellers going back into the past cannot alter the past (i.e., the past is deterministic). This is because quantum objects can act sometimes as a wave. When they go back in time, the various probabilities interfere destructively, thus preventing anything from happening differently from that which has already taken place.
As a side note, those interested in the various ways time-travel seems to work in SF novel should run to the Guide To SF CHRONOPHYSICS.
Why have you not read about this in any science fiction novel?
It is absent from some because the authors do not know enough relativity theory to spot the FTL equals Time Travel implication.
It is absent from the rest because of those who do know enough relativity, practically no author wants to deal with the huge squirming can of worms opened by time travel. They just wants a quick and easy way to get their hero from star to star.
This is why the time travel connection is the dirty little secret of science fictional FTL travel.
It seems to me that an FTL drive ruled by the Novikov self-consistency principle would operate in a very strange and non-intuitive way. It might be that occasionally the starship pilot would set up a trip and the FTL drive would refuse to operate. Then the pilot would know that somehow someway the proposed trip would cause a paradox.
Or even worse, after an FTL trip, the pilot and any passengers would discover that if they try certain actions the entire universe throws up random events preventing said actions. Indeed the entire universe might throw up random events forcing a passenger to perform some action. Because if certain actions happen or certain actions do not happen, a paradox will ensue.
If I'm understanding how it works it correctly, the way to use your FTL starship as a time machine is to make your way at FTL speeds to say, Alpha Centauri, and then travel at sublight velocities in the direction directly away from Sol. When you then return to Sol at superluminal speeds, you will have travelled back to a point in time a number of years equal to the distance in light years you travelled sublight away from Alpha Centauri.
So if you want to get back before you first leave, take a little detour.
NoXion
Craicy the Squirrel
I thought you were talking about the time dilation brought about by travelling at high relativistic speeds (i.e. less than lightspeed but still damn fast), which only allows one to travel into the future. Whereas I'm talking about FTL travel which would (according to relativity) allow one to travel into the past.
Oh wait, I found it. I think.
Yeah, further back up thread than that. Long way back.
Supine
Newt Member
When I moved to Earth 347 years ago I used a technology like FTL but also very different. I expect humans to develop the correct knowledge in about 3000 years if they aren' invaded first.
Obviously I can't help you out with tips as our home planet are building up an invasion force as we speak. May7th this year could be interesting, thats all I'm saying...
Obviously I can't help you out with tips as our home planet are building up an invasion force as we speak. May7th this year could be interesting, thats all I'm saying...
camouflage
gaslit at scale.
I hope you realize that it is forbidden to poach from this wildlife preserve, and suggest you think again, or face a hefty fine.
But the DE is just a long-winded tautology.
And the thing about tautologies is: They're TRUE.
EastEnder
Brixton Barnacle
The Drake Equation is a master stroke of self publicity that would be the envy of snake oil salesmen everywhere.
If we knew this, this, this, this, this, this, this, this and this, then we'd know that.
The man is famous for an equation that tells us precisely fuck all.
EastEnder
Brixton Barnacle
It may have the whiff of verisimilitude, but I think that's an illusion. Worst of all, I think it's profoundly unscientific. I say that because it's not testable - it's a set of terms for which we don't know the values, therefore we can not test the equation. That does not make it incorrect, but does relegate it to the realm of pure speculation. And as such, I do not think it deserves the recognition it is popularly afforded.
EastEnder
Brixton Barnacle
Einstein's equations are testable, that's what makes them scientifically valid (not necessarily true, just scientifically valid).
Something that's not testable is not inherently wrong, but it should not be regarded in the same light as something that is. That's all I'm trying to say.
littlebabyjesus
one of Maxwell's demons
Einstein's equations contain information. Drake's don't.
stdP
One Swiss dinosaur in Polly Gosling's anorak hood
I think you're drastically over-estimating the age of the universe; current estimates are at about 13.8 billion years old. Our own solar system, the important bit of it anyway, is about 4.5 billion years old and it's thought to be a third generation star (technically I think called a Population 1 star because of its relatively high metal content - means it's formed from at least two previous stars).
Don't think there was much chance of any intelligent life around 1st generation stars because there wasn't really anything other than hydrogen lying around; life as we understand it is only likely to evolve around Population 1 stars; else there's not really anything in the way of raw materials to make planets and complex chemicals out of. So it's reasonable to assume that advanced life in our galaxy could potentially have arisen in around about the same billion years or so as it has on earth.
Personally I'm of the opinion that intelligent life elsewhere in the universe is a statistical certainty, but our chances of ever encountering any are so mind-bogglingly small that you could get away with saying "for all intents and purposes aliens might as well not exist". I'm not saying never, because never is a time even longer than the lifespan of the universe, but even just detecting our TV and radio transmissions from a few hundred light years away (assuming civilisation a few hundred light years away has developed/is still using anything as appallingly stone-aged as radio waves) is an impossible feat, because we've only been throwing out radio signals for a century or so. Our current "we are here" beacons are literally invisible before you even consider the possibility than the Vlorgplaxians stopped watching TV 500 million years ago and have been watching Vlorgplaxianflix over sub-ether ever since. The same problem applies to us, as all of our current detection techniques are still based on the EM spectrum. Let's say by some miracle we did pick up a transmission of VlorgplaxiEnders or Hubble took snaps of someone building a dyson sphere... it's something that may well have happened hundreds or thousands of years ago from a location that was quite possibly no longer exists, how would we even begin to think about sending back a message...?!
Draw a sphere 100 light years in radius around Sol (so 200ly diameter) and you still get a monstrously tiny speck in the middle of an average-sized galaxy (100-200 thousand light years across and about 2000ly thick where we are). The nearest galaxy to ours, the relatively puny Canis Major Dwarf, is relatively near at only 25,000ly away (yes, we're closer to another galaxy than we are to the centre of our own). A a great man once put it: "Space is big. Really big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist, but that's just peanuts to space." As the same man put it even more succinctly, "The simple truth is that interstellar distance will not fit into the human imagination."
I don't think detection of alien civilisations is even a starter until FtL communication or travel are a reality, and the last time I asked the laws of physics she said we were still a long way off inventing the Sonic Grummoxyplunger.
Well said. There's loads of these variable that are nearly impossible to even take a guess on without finding an advanced alien civilisation first and studying their planetary history.
Even after you get yourself a rocky planet with plenty o' water and a magnetic field into the Goldilocks zone of a main-sequence Pop1 star, creation of life is still a huge "dunno really".
Aside factoid: It's often thought of that our moon (which as some of you might know is highly weird by virtue of the way it was thought to have formed) might have been a major factor in the formation of life with its tidal effects; it was much closer to earth and created tides that were mind-bogglingly massive, tidal ranges of the order of 100m or more rather than the 15m or so we see today. That continual ebb and flow (that makes it sounds gentle though - wouldn't have been. Would have been like a tidal wave hitting the beach once every 4 hours, a bit like that pond-planet in Interstellar) of the seas across the newly formed land - forming extensive, isolated yet regularly-refreshed shallow pools to soak up sunlight and get struck by lightning - is thought to be a key factor in life originating on this planet, and we already know that moons like ours are apparently quite uncommon.
Apols for mini-rant, been wanting to post in this thread for yonks but never had the time, still don't, but there was my semi-cogent post anyway.
NoXion
Craicy the Squirrel
Why would FTL be needed? Is spectroscopic analysis of exo-planetary atmospheres focusing on artificial chemical compounds somehow not possible?
bi0boy
Power User
I could imagine aliens looking at earth from afar and thinking "can't be any life there, it's wracked by massive tidal forces from its weird moon creating unusually unstable conditions - life needs conditions like those found on our planet, with its eccentric orbit allowing long periods of stable conditions with the occasional heat of perihelion to facilitate the necessary chemical reactions"
NoXion
Craicy the Squirrel
Especially if they were looking at our planet when the moon was recently formed.
stdP
One Swiss dinosaur in Polly Gosling's anorak hood
Certainly possible, although personally I'm not convinced such a thing is a reliable detector of whether there's a civilisation there or not. Unless you can pop over there and take a gander at it yeself or send a friendly phone call and get a "Why yes, we ARE creating a planet made entirely from blancmange!" in response I'm not sure our current detection methods and metrics are up to snuff. Stuff like the James Webb 'scope might well be a game changer for that but for now I'm still happily on the cynical wump side.
Indeed, their version of the Drake equation may be just as useless as ours
NoXion
Craicy the Squirrel
Absolute certainty will always be out of reach, but we can still make inferences based on the balance of probabilities. For example, if we were to analyse the light from an exo-planet and find both oxygen and CFCs within it's atmosphere, that would certainly put more points in the "probably has a technological civilisation" column. A quick Google suggests that at least some CFCs occur naturally through volcanic eruptions, so the presence or otherwise of other elements or compounds might be useful as well. Long-term observations of potentially inhabited worlds could also turn up anomalies or trends difficult to explain in entirely naturalistic terms.
weltweit
Well-Known Member
Suggesting that not only are they tech but also, they have fridges and deoderant!
NoXion
Craicy the Squirrel
Or giant ground-based lasers that need lots of coolant, some of which occasionally leaks out into the atmosphere because that's what happens when an ICBM gets through the missile shield and hits one of them.
It isn't. It's 299792458m/s precisely, by definition.
bi0boy
Power User
Not when Einstein was alive it wasn't, because the meter was defined differently.
littlebabyjesus
one of Maxwell's demons
By observation. By measurement.
You'd need a theory of everything to be able to claim that was light speed by definition, no? Be cool to be able to.
I think the point is that the metre and/or the second (can't remember which) is defined so that light speed is precisely that number.
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