Well, with that attitude, no clone is going to want to be entangling with your consciousness anyway!
Szydagis' point 3: Interstellar travel is too hard
- Thread starter Ann K
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Well, with that attitude, no clone is going to want to be entangling with your consciousness anyway!
Gary C
Active Member
This is an updated version of my reply from an earlier thread. The Fermi Paradox comes up eventually on every astronomy and space forum and social media site I visit so I now keep a canned response on file.
Hope this helps.
There was some vintage sci-fi novel, by Moorcock or someone of his era, musing on the difficulties of time travel and envisioning it as trying to move all your molecules against a river of all the other instances of your molecules in those post iterations. At best you're converting yourself into the same configuration of yourself at a past state; there would be no future "you" consciousness to be aware of the past; worst case you dissolve, possibly turning back into all the nutrients you've ever digested.
Scaramanga
Senior Member
There's no Fermi paradox if there's nobody else out there....at least within any detectable range.
People have this bizarre idea that there 'must' be other life out there because there's so many planets. But that is bad science and bad statistics. One cannot possibly argue a 'must' based on a large number...when the odds against life forming may be an even larger number.
Simply being impressed with the number of planets is a fallacy. We have a sample of one. We simply do not know if it is 1 in a million or 1 in 10^527, and there is nothing that guarantees that the odds against life are smaller than the number of planets.
Scaramanga
Senior Member
Well, I could get in my time machine that I created yesterday and go back to yesterday and pick up myself and bring past me to today. Then we could both go back and meet the two of me from yesterday and bring them to today. And pretty soon I could exponentially, in powers of 2, create more 'me' than there are atoms in the entire universe. If that's not proof that time travel to the past is impossible then I don't know what is.
Mendel
Senior Member.
you'd be indistinguishable except for your history
nobody could prove you're not you
that's why cars carry serial numbers
Mendel
Senior Member.
no, you couldn't
if you change spacetime such that you don't exist from Monday to Tuesday, then there is no "you" on Tuesday that existed through this time. The result of this time travel is one "you" on Tuesday either way, you can only change how it gets there.
Mendel
Senior Member.
That's teleportation.
I expect that reversing the flow of time directly violates the second and third laws of thermodynamics (about entropy increasing).
Eburacum
Senior Member.
If the universe allowed time travel, I'd expect a flood of refugees coming back from the Heat Death of the Universe to live in our more comfortable environment; this would happen exponentially (and instantly), causing the universe to collapse in a Big Crunch due to the excess (unconserved) mass. This hasn't happened, so time travel is likely impossible.
Todd Feinman
Active Member
Would you be going back to the same universe if time travel were possible? Or an alternate? At least with the block conception of the universe, it would be an alternate, I think.
JMartJr
Senior Member.
Unless time travel does not work that way. Either paradoxes (at least as viewed without time travel) are integral to the fun of time travel stories, and since time travel is, so far, totally fictional, I'd rule that time travel paradoxes are definitely allowed.
Spoiler -- if you have not read "Flight of the Horse" and other tails of Hanville Svetz, reluctant time traveller, but might someday, skip this:
In the stories, Svetz and his associates travel back in time from a post-semiapocalyptic future to a past from which only fragmentary records survive, in search of interesting animals that went extinct when humans wrecked the environment. What they don't know is that, since time travel was always considered fictional, when they go back past the date of the invention of the machine, they slide across timelines into fictional universes. So Svetz is surprised when the horse he went to capture almost kills him with it's spiral horn, and he suffers major burns when the gila monster lizard, which is MUCH bigger than expected, breaths fire all over him while flapping it's vestigial bat wings...
More worrisome, would you come BACK to the right universe? Svetz's machine gets around that by having the massive machinery of the time machine stay firmly in his present, in the Institute for Temporal Research, while just poking the "extension cage" back into time. It is said that the viewof the side of the cage that extends back through time to the rest of the machinery is disconcerting... but at least when you go home, you are reeled back in to where you started.
Eburacum
Senior Member.
Niven (who wrote the Svetz stories) also discusses an interesting temporal conjecture - the Chronological Protection Conjecture; in any universe where time travel is invented the historical timeline keeps changing until time travel is never even invented, which is the only stable condition.
Eburacum
Senior Member.
I agree, and that presumably means we are in an alternate without time travel, which is probably a good thing.
LilWabbit
Senior Member
But also the time jump itself causes the same energy from the future to cease to exist in the future and thus preserving the overall conservation of energy in the totality of spacetime -- if T-symmetry is indeed postulated. However, T-symmetry remains a highly disputed postulation amongst theoretical physicists as there remain strong grounds to postulate the arrow of time.
Causality, however, is a whole other kettle of fish. Many a philosophically untrained theoretical physicist and their avid followers/listeners have incorrectly hijacked this far broader and more fundamental philosophical notion (causality = a thing -- whether entity, property or behaviour -- having a cause) to mean that a cause precedes the effect in time whereby causality is inextricably bound by time. And yet even within physics there are causes of behaviours, properties and entities that happen simultaneously with the effect where invoking any notion of time is meaningless.
To hark back on this thread to John Wheeler's encapsulation of Einstein's relativity: 'Spacetime tells matter how to move; matter tells spacetime how to curve.'
More precisely, in relativity spacetime causes matter to move along certain pathways whilst matter somehow causes spacetime to curve. Whatever be the best formulation of this principle, anything causing spacetime to curve is by logical necessity meta-spatiotemporal and perfectly instantaneous rather than time-bound. In other words, matter causes time itself to behave in a certain way and therefore demonstrates a causality that necessarily occurs outside/beyond time and refutes the more limited definition of causality as being something necessarily time-bound.
Similarly, other physical laws -- such as the second law of thermodynamics whereby the entropy of isolated systems is bound to increase (receiving no harnessed energy from outside the system to decrease entropy) -- is by necessity meta-spatiotemporal. All of the universe seems to follow this principle based on all observations leading us to conclude, in causal terminology, that such a law causes certain behaviours instantly and simultaneously with the cause rather than the effect following the cause in time. Similarly, few would dispute that the sun is the cause of its radiation. And yet there's no way of clearly determining whether sun precedes in time the point at which it first generates radiation. And so on and so forth. Physics is full of what's called 'essential causality' in philosophical ontologies as opposed to studying merely 'causalities of time'.
Leibniz's Principle of Sufficient Reason (i.e. everything has a cause / sufficient reason) is perhaps the most famous articulation of causality and in many ways most working scientists, irrespective of discipline, assume it (wittingly or unwittingly) as a basis of their work. That is to say, they consider their main objective as scientists to be a quest for observer-independent (objective, realist) explanations to observed phenomena by trying to answer the question 'What causes this observed behaviour / entity / property?' PoSR is philosophically deliberately non-specific as to the type of reasons or causes implied -- say, time-bound causes or non-time-bound causes. In other words, any entity, property or behaviour can theoretically have (1) both deterministic or indeterministic causes ('law-likeness' vs. 'chanciness'). The entity, or its property or behaviour, may have (2) causes both/either within the entity (self-caused) or outside the entity (other-caused). And yet (3) causes may be total causes (causes for the very existence of an entity) or partial causes (causes for a particular property or behaviour of an entity). And yet furthermore, and closely related, (4) causes may be composite (many causes) or simple (single cause). Even the foregoing list of four types of causes is not exhaustive in terms of all logically possible types of causes.
All of the above types of causes are worth exploring in any exercise purporting to describe itself as 'scientific', not just causalities of time. What PoSR squarely disagrees with is the philosophical alternative that an entity, property or a behaviour can be/occur without any cause whatsoever. This fundamental rule posited by the PoSR is often justified by appeal to the philosophical dictum ex nihilo nihil fit ("nothing comes out of nothing").
According to the dictum, while it's logically possible that there be an entity or a property that has no cause whatsoever, it's an absurd and unhelpful possibility. Hence, for instance, the known universe may be, under the PoSR, rationally explored either as having a sufficient reason within itself for its own existence (self-caused) or without itself (other-caused). But the third option that there is no sufficient reason for the universe to exist is regarded as absurd, for the question can always be reasonably asked: If the universe does not have a sufficient reason to exist at all, how come it exists nonetheless? The proponents of the third option forbid the question 'why' or 'how' and insist on acceptance of its existence as a brute fact.
Footnote: Philosophically the question 'what causes time?' (irrespective of whether time has an infinite past or not) is perfectly reasonable and hence the simplistic and popular physicalist understanding that causality logically necessitates a cause-and-effect relation in time is both incorrect and superficial. Hence, a self-caused universe that has always existed is a perfectly logical statement when understood in terms of 'the universe containing within itself a sufficient reason for its own existence'. Similarly 'a universe that has always existed may have a sufficient reason for its existence outside of itself' is also perfectly logical. The key takeaway here, however, is that this dilemma is a metaphysical (philosophical) one and hence unresolvable scientifically. Any effort to do the latter stumbles upon a category mistake.
FatPhil
Senior Member.
It is highly improbable that it's 1 in 10^527 *because* we have a sample of one.
The true neutral stance is a poisson one, which says that the chance of there being life on other planets is 42%. And no, that's not a joke, that's 1-e-1/(1-e-1). Everything else is assuming something.
Mauro
Senior Member
But, you are neglecting the survivorship bias. Our sample of one (the Earth) is terribly biased, because we must have been born on a planet which harbors life, or else we would not be here to ask ourelves questions. So having this sample of one means exactly nothing, and the poissonian calculation is not neutral.
From the data we have, the best we can say is the probability of a generic planet harboring life is between say 1/5000 (one, the Earth, divided by the number of known planets) down to, possibly, even 10^-527, who knows.
JMartJr
Senior Member.
One slight bit of meaning that can be extracted -- we know the chance of life arising (and eventually becoming intelligent and spraying the surrounding universe with radio waves and small chinks of worked metal) is not zero! Not useful for doing the probabilities, as the chance COULD still be 1 in (number of planets that exist), or worse, in which case we might be the whole ball game.
FatPhil
Senior Member.
I am not ignoring survivorship bias - I am using our survivorship as the input into the equation, and nothing else. The only assumption is that there's nothing intrinsically special about the earth in the region of space we're considering (thus sampling behaves like a random process). The unknown unknown in that is how large that region needs to be in order for that assumption to hold true. We're made from the same elements from the same kinds of supernovae that have condensed into the same kinds of solar nebulae as all of the other planets out there, so it would be a brave stance to assert that that region is larger than the known universe. It's correct, however, to point out that I am ignoring the 5000 exoplanets presumed to not carry life, and superficially that looks like a fatal oversight. Fortunately, when the region of space under consideration is large enough that we are not an intrinsically special planet, these exoplanets likely become not intrinsically special too.
And as I said, the bayesian view is that the probability being 10^-527 has very low credibility (a similar order of magnitude to that probability itself). At no point did I say it's an impossible value. And the upper credible bound wouldn't necessarily be 1/5000 either - we're not necessarily sampling fairly, we might be unfairly selecting planets with disfavourable temperatures or gravity.
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