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Travel through wormholes is possible, but slow

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Re: Travel through wormholes is possible, but slow

#151

Post by naasking »

harimau777 wrote: post #136
nine_k wrote: post #81

Earlier quoted context omitted.

This depends on what do you mean by 'inaccessible'. Going there and back again, and telling your pals how things are 1000LY away is likely impossible. Expanding your civilization to more and more habitable celestial bodies, slowly but relatively surely, is entirely possible. This is how e.g. plants colonize vast spaces, being limited by the speed of their growth often by inches per lifetime. (You should also consider…

I get what you are saying, but it seems like the plant approach is mostly useless to humans. If the people on opposite sides of a galactic civilization are so far away that they cannot meaningfully interact, then it seems like that's no different than the other person not existing from their perspective.

> I get what you are saying, but it seems like the plant approach is mostly useless to humans

Yes, and as humans are to plants, so our space faring descendents will be to us.

Re: Travel through wormholes is possible, but slow

#152

Post by krastanov »

naasking wrote: post #150
krastanov wrote: post #144

Earlier quoted context omitted.

Mathematical theorems (especially no-go theorems, one of the most powerful tools in physics) are at least as much of a fact as an experimental measurement. I can concede that a pop-sci outlet should be clear about what is an experiment and what is a mathematical theorem, but was it really not clear in this case? This is a sincere question, and I care to hear your opinion: do you believe that a reader of phys.org woul…

> Mathematical theorems (especially no-go theorems, one of the most powerful tools in physics) are at least as much of a fact as an experimental measurement That's an overstatement. Measurements are more important than theory. We cannot form theories without measurements, and yes theories inform our measurements, but science always begins and moves forward with measurements.

General relativity, quantum computing, some parts of thermodynamics/information theory/statistical physics, some parts of quantum field theory, some parts of condensed matter physics are all things that started as purely mathematical statements. I am not trying to diminish the monumental importance of empirical measurements, but please do not diminish the importance of logical consistency and mathematical constraints. We can say a lot about our universe with great certainty even though in same cases making direct measurements is orders of magnitude beyond our technology.

Re: Travel through wormholes is possible, but slow

#153

Post by dbasedweeb »

krastanov wrote: post #152
naasking wrote: post #150

Earlier quoted context omitted.

> Mathematical theorems (especially no-go theorems, one of the most powerful tools in physics) are at least as much of a fact as an experimental measurement That's an overstatement. Measurements are more important than theory. We cannot form theories without measurements, and yes theories inform our measurements, but science always begins and moves forward with measurements.

General relativity, quantum computing, some parts of thermodynamics/information theory/statistical physics, some parts of quantum field theory, some parts of condensed matter physics are all things that started as purely mathematical statements. I am not trying to diminish the monumental importance of empirical measurements, but please do not diminish the importance of logical consistency and mathematical constraints…

GR was amazing, but it wasn’t well known and accepted until the first measurements confirmed it. Quantum Computing is still very much up in the air, but it’s also weird to bring it up in this context, because QM is one of the most tested theories of all time. QED In particular is tested to the most decimal places of any prediction, ever. It’s also weird to act as though GR and QM started out in a vacuum, instead of what they really were, which was based on centuries of math, theory, and experiment.

Edit: Unrelated, but I see you’re a fellow Greg Egan fan, good to meet you! Planck Dive has to be one of my all time favorites.

Re: Travel through wormholes is possible, but slow

#154

Post by krastanov »

pmiller2 wrote: post #149
andbberger wrote: post #135

Earlier quoted context omitted.

I think it goes beyond the scientific press. There seems to be a general tendency to squash the intricacies of anything and react impulsively to some red herring or whatever; such comments dominate all online forums I've ever seen. Here is a fantastically interesting article that maybe has some new insight on the nature of spacetime; top comment on HN thread about it is some person loudly and incredibly pretentiously…

IMO, your premise is a strawman. I don't detect any "it's just a theory" sentiment in the top level comment. What the comment says is that mathematical statements about "hitherto unestablished and untested theories" should not be taken as statements about the world. This, to me, shows a rather sophisticated understanding of scientific truth, namely that we should demand that a scientific theory (as opposed to a mathe…

There is an important point you are not addressing: it is one thing to make a statement about one single mathematical construct (it is cute, but not a big deal). It is another thing to make a statement that constrains a whole family of seemingly disconnected mathematical constructs (this is now a serious constrain on what the laws of the universe can plausibly be).

From a sibling comment:

> There are some results around QG, such as holography, which seem to be universal. That is, they make sense with strings, loop quantum gravity or any of about ten other lines of work that people can do quantum gravity calculations with today.

> If you can prove that all of those have to say the same thing, that is a powerful result and probably means something about our world.

Re: Travel through wormholes is possible, but slow

#155

Post by krastanov »

dbasedweeb wrote: post #153
krastanov wrote: post #152

Earlier quoted context omitted.

General relativity, quantum computing, some parts of thermodynamics/information theory/statistical physics, some parts of quantum field theory, some parts of condensed matter physics are all things that started as purely mathematical statements. I am not trying to diminish the monumental importance of empirical measurements, but please do not diminish the importance of logical consistency and mathematical constraints…

GR was amazing, but it wasn’t well known and accepted until the first measurements confirmed it. Quantum Computing is still very much up in the air, but it’s also weird to bring it up in this context, because QM is one of the most tested theories of all time. QED In particular is tested to the most decimal places of any prediction, ever. It’s also weird to act as though GR and QM started out in a vacuum, instead of w…

We are talking past each other: It is a bit contradictory to say "quantum computing is up in the air" and "QM is one of the most tested theories" as an argument against what I am saying. Yes, both are statements are true, but they are in no ways counterpoints to what I am saying, if anything they support it. QM is a well established and empirically tested theory. Quantum Computing is a purely mathematical construct that emerged from that well established theory without any experimental evidence for it, and only now, 30 years later, we are starting to have a chance to employ this purely mathematical construct in practice.

Same with GR: it was a purely mathematical construct for a while until we could test it, but there were too many theory clues that it must be right.

And this is not selection/survival bias: it is extremely rare for humanity to find a robust mathematical construct for which we can have a high degree of certainty that it describes the universe well. In the few cases where we have had that certainty, due to mathematical proofs in seemingly disjoint fields, we ended up being right.

To push it to stuff like super strings and quantum gravity: few respected scientists would claim that their pet mathematical construct is correct, but many of them will say "the vague commonalities between all these diverse and seemingly unrelated mathematical constructs definitely point to an underlying fundamental construct".

Re: Travel through wormholes is possible, but slow

#156

Post by pmiller2 »

krastanov wrote: post #154
pmiller2 wrote: post #149

Earlier quoted context omitted.

IMO, your premise is a strawman. I don't detect any "it's just a theory" sentiment in the top level comment. What the comment says is that mathematical statements about "hitherto unestablished and untested theories" should not be taken as statements about the world. This, to me, shows a rather sophisticated understanding of scientific truth, namely that we should demand that a scientific theory (as opposed to a mathe…

There is an important point you are not addressing: it is one thing to make a statement about one single mathematical construct (it is cute, but not a big deal). It is another thing to make a statement that constrains a whole family of seemingly disconnected mathematical constructs (this is now a serious constrain on what the laws of the universe can plausibly be). From a sibling comment: > There are some results aro…

I'm not exactly sure which version of "If you can prove that all of those have to say the same thing...." you're arguing for. It doesn't scientifically matter what statements you can make about any number of mathematical constructs if none of those constructs make testable predictions. Remember, falsifiability is a necessary condition for a construct to be a valid scientific theory.

OTOH, it does matter if you are able to make a statement of the form "Any mathematical construct that accurately describes X must have property Y." It is not clear that quantum gravity (or the linked article) meets this latter standard.

Re: Travel through wormholes is possible, but slow

#158

Post by p1esk »

throwawaymath wrote: post #139
dfox wrote: post #130

Earlier quoted context omitted.

Modeling a mind as giant stimulus->response is similar issue as "breaking" an block cipher by building exhaustive input->output map, which for 256b blocks almost certainly requires more resources than is contained in whole known universe. On the other hand while uploading minds probably has some issues, it involves replicating thing that we can assume resides in physical space, the question remains as to how and whet…

I can see why you're drawing a comparison between enumerating stimulus -> response correspondences and "breaking" encryption using a lookup table. But I don't agree that the two would be comparable in difficulty a priori . First, encryption schemes typically try to complicate their linear structure by design, such that inverting the sequence of linear transformations can't be done without (ostensibly) secret informat…

how to 1) replicate a human mind via as of yet nonexistent direct brain-interface technology

I’d say this is an engineering problem, rather than #2, which is philosophical. For #1, all you really need is to measure all brain cells accurately enough, then recreate the whole thing in a simulation. Could probably be achieved with nanobots or very advanced scanners within couple of centuries. Might be acceptable to destroy the original in the process, if it makes it more feasible.

Re: Travel through wormholes is possible, but slow

#159

Post by krastanov »

pmiller2 wrote: post #156
krastanov wrote: post #154

Earlier quoted context omitted.

There is an important point you are not addressing: it is one thing to make a statement about one single mathematical construct (it is cute, but not a big deal). It is another thing to make a statement that constrains a whole family of seemingly disconnected mathematical constructs (this is now a serious constrain on what the laws of the universe can plausibly be). From a sibling comment: > There are some results aro…

I'm not exactly sure which version of "If you can prove that all of those have to say the same thing...." you're arguing for. It doesn't scientifically matter what statements you can make about any number of mathematical constructs if none of those constructs make testable predictions. Remember, falsifiability is a necessary condition for a construct to be a valid scientific theory. OTOH, it does matter if you are ab…

Ah, I think we have a deep "philosophy of science" disagreement. Basically, it is not just "falsifiability", but also "probability" of being correct. Probability that can be informed by things like formal versions of Occam's razor (e.g. Kolmogorov complexity, Akaike information criterion, etc).

Here are a few premises on which I based my statement (I will pick one particular venue of scientific research, so I will not speak in all generality. You can of course disagree and say that it does not generalize at all, but I think this would be a philosophical discussion, i.e. it does not matter at all that we have different opinions, as both are equally valid ways of pursuing scientific truth):

1. Computational complexity is a science on its own. Computational complexity also makes useful statements about the limits of the physical laws in our universe (a la "extended Church-Turing thesis" or Aaronsons "NP-complete problems and physical reality").

2. NP=P vs NP!=P is a question that has a definite answer within the relm of science but we do not know the answer yet. The answer will constrain what the permitted laws of physics are due to point 1 above.

3. There are a lot of clues that NP!=P coming from very separate disjoint fields of math. Mainly because we already know there are a lot of "phase transition"-like phenomena when we apply approximate algorithms to problems that can be parameterized to be NP-complete only if some ε is larger than some critical value.

4. These "phase transitions" are purely mathematical constructs, but due to the previous points they constrain what is permitted in the universe as strongly as any 5-sigma measurement in a particle accelerator.

To bring this back to the discussion of speculative theories of quantum gravity: if all of the competing theories of quantum gravity (all of them being very speculative and unproven) have a handful universally agreed on predictions (although derived in completely separate ways), this is as strong of a constraint as any 5-sigma measurement in a particle accelerator or cosmological observation.

Or if you permit me to attempt to phrase is it in yet another way: there are a ton of theory assumption behind any 5-sigma (or 10-sigma) experimental measurement. These assumptions are the same ones that inform the purely mathematical constraints. If both the math constraints and the interpretation of an experiment are based on the same assumption, why are you taking the interpretation of the experiment any more seriously than the pure math.

Sorry for the length of this text - I am finishing my dissertation this week (doctorate in physics), so this is very much on my mind at the moment.

Re: Travel through wormholes is possible, but slow

#160

Post by VRay »

TeMPOraL wrote: post #131
hinkley wrote: post #124

Earlier quoted context omitted.

I suspect if you had that much understanding of orbital mechanics, you'd be a billionaire already and not worry so much about time travel.

No sensible protagonist or villain use time travel to become a billionaire. There are usually better pursuits involved.

Except Biff of course
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