Physics discussion: FTL drives, Speed of Light, Life in the Universe, etc

  1. Serendipity

    Serendipity Well-Known Member

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    If the human race does not kill itself with stupidity, faster than light travel will happen in some form or another.... still have headaches about the real implications of that...
     
  2. Vertigo

    Vertigo Mad Mountain Man

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    ????? How do you figure that?
     
  3. Serendipity

    Serendipity Well-Known Member

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    Apart from the work on Alcubierre's Drive and Quantum Entanglement you mean?
     
  4. Vertigo

    Vertigo Mad Mountain Man

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    Quantum entanglement is not travel, though FTL data communications using it may be possible, and the Alcubierre drive is still only a speculative and unproven concept, really no more likely than wormholes or even hyperspace. I still think the strongest explanation of the Fermi paradox is that FTL travel is simply not possible. (Sadly... believe me I'd love for it to be possible :))

    The problem with quantum entanglement for communication is that you need to have entangled particles at each end of the communication 'channel' but they must be created together, therefore after creation one must be transported to the other location and that can only be done at a maximum of light speed. So to use quantum entanglement to communicate between two points say 10 light years apart you must first wait ten years whilst the entangled particles are sent from one point to the other. Then in order to have meaningful communication you need at least millions of such particles.

    ETA: Charles Stross deals with this entanglement problem quite neatly in Singularity sky where your supply of entangled particles for communication is finite and, like a battery, is useless once used up until you can get more entangled particles.
     
    Last edited: Jul 17, 2017
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  5. Mirannan

    Mirannan Well-Known Member

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    I don't think that lack of FTL is a viable explanation for the Paradox. Someone said it well: "Looking for evidence of technological activity in an inhabited Galaxy ought to be like looking for such evidence on Manhattan Island".

    Without FTL, an expanding civilisation would be more or less forced to use as much as possible of the resources of a single solar system -which leads to the formation of a Dyson swarm quite quickly. (Certainly compared to the lifetimes of stars!)

    The signature of such a swarm would be an object with the luminosity of Sol (approximately) but with a spectrum roughly corresponding to a blackbody at a temperature of around 300K, if the people are anything like us, perhaps with occasional weak flashes of visible light. (From gaps in the shell.) I'm not aware that anyone has ever looked for those.
     
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  6. SilentRoamer

    SilentRoamer Well-Known Member

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    Not sure why you would think this...

    Sorry what "work" on an Alcubierre drive are you talking about? This is a purely theoretical mode of travel, it talks about the contraction of spacetime ahead of the object and expansion of spacetime behind it and hasn't had serious scrutiny or revision for a while, whilst all sounding very good it is completely theoretical and hinges on properties of spacetime we are not even sure exist.

    With Quantum Entanglement - nothing actually goes FTL, the information is already present in the photon just a measured state does not exist. Nothing is physically transported.

    Whilst I agree that progress marches ever on there are certain principles in physics which we expect to hold true. The speed of light to all observers is one of these things, if the speed of light were to be surpassed then it has all sorts of implications for our understanding (or lack thereof) of known science.

    Theoretically an Einstein-Rosen bridge has the ability to "allow" ftl travel through remotely connected regions of space, along with CTC's and other postulated theoretical spacetime metrics - although they are only theoretical.

    Unfortunately I think we are approaching the Golden Age of humanity - we may already be there right now.
     
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  7. Serendipity

    Serendipity Well-Known Member

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    OK - several points to reply to here - so bear with me....

    1. Alcubierre's Drive - further work was done beyond the original paper, which started to identify how to take the theoretical to reality. All I remember is it was done in this century. Although there is a long way to go, we have already taken a step in the right direction. I would over time expect even more work to be done on the road to making this a reality - if other methods etc don't get there first.
    2. Quantum Entanglement - yes, at the moment, you would need to have quantum entangled particles travel sub light speed before they can be used. However, once set up correctly, a thing or person or alien could use the quantum entangled particles to move data from one place to another. To the newly come user this would appear to be travelling faster then light. It all boils down to relativity - sorry couldn't resist that pun. A good novel that describes this as best as s/he knew it at the time was Greg Egan's Child's Ladder.
    3. The final point is perhaps going to the most controversial. The homo sapiens has at the most been around for 1.8 million years, though could have developed any time up to 200,000 years ago. Now let's start stacking up the probabilities of the human race having been able to survive global disasters since then e.g. surviving the nuclear race, worldwide killer virus epidemic etc etc. Bottom line is either the human race has been very lucky or it has had some kind of guidance to survive. Ramifications of either situation I'm going to leave to your all too vivid imaginations, except for one point - faster than light travel does allow you to go back in time - and this is where my brain hurts...
     
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  8. SilentRoamer

    SilentRoamer Well-Known Member

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    I will always bear with you - even if I may respectfully disagree. I believe we can have these differences of opinion and still be measured and civil! :)

    Ok so The Alcubierre drive - the problem I have is that we have to compare apples and oranges when looking at this compared to the existing fruit of human labour and the reason I say this: although our understanding of physics has changed over the centuries and decades it is as complete as it has ever been. The Alcubierre drive isn't based in the realm of scientific plausability because it does a number of things:

    1. It assumes a number of intrinsic properties of spacetime (note we need to use the word spacetime here as the method of compression must deal with einsteinian and not newtonian understandings of the interconnected nature of spacetime, namely that time and space are not discreet.)
    2. It assumes an ability to somehow "control" spacetime at a fundamental level.

    Now obviously we can only look at this from the perception of modern man - no doubt an ancient human would balk at the notion of flying metal. However we do have the best understanding of physics we have ever had and the invariable speed of light is a constant that appears to hold true over the entirety of the Observable Universe. Laws of isotropy and homogeneity dictate this is the most likely state of the remainder of the unobservable U, whether finite and bounded and infinite and unbounded.

    Ok I think you understand Entanglement but your terminology is a bit confusing. You talk about "moving" data but nothing is ever actually moved. Another problem - the most fundamental problem, is that Entanglement is random until observation. It's like me sending you a box, and keeping a box myself, I know whatever is in my box is also in your box, fantastic! Except I don't know what's in my box until I measure it and I have no way of controlling the result of the measurement. As I have argued - this has more applications for secure communications than it does for instant data transfer, especially as anything on geological scales is minuscule compared to the speed of light.

    FTL does allow time travel you are totally right! So many people fail to accept this but it is mathematically unassailable.

    Interesting discussion. :)
     
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  9. Ursa major

    Ursa major Bearly Believable Staff Member

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    Not in the case of photons, as far as I can c....
     
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  10. Serendipity

    Serendipity Well-Known Member

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    Oh groan.... but you're right... but we're still limited to the speed of light.
     
  11. Serendipity

    Serendipity Well-Known Member

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    1. I'm always happy to join in a healthy constructive debate... ;):) After all that's how a lot of scientific progress ends up being made.

    2. Alcubierre's Drive - I remembered correctly that there has been further work done since the initial paper came out in 1994. It involves changing the warp bubble into a warp ring. This was being worked on by NASA in 2012, but I haven't seen any reports since then. I believe they were setting up an experiment to see if they could measure the warpedness (is there such a word?) of the Alcubierre metric - part of the theory behind the drive. (The fact that we have not seen any results published means nothing - the Americans sometimes classify promising results for national security reasons - I'm not saying this is the case here - we just don't know.)

    3. Quantum Entanglement - the principles you describe are correct in essence. However, there is a mechanism of effectively having the same type of event occur instantaneously at the same time at a distance. I would argue that there should be a way to engineer getting composite signals across that same space, particularly when you consider that communications engineers have already developed a large cadre of signal analysis and correction methods, which I believe would help in such a situation.

    4. Agreed faster than light travel could lead to time travel - which is why this does my brain in!:eek:
     
  12. SilentRoamer

    SilentRoamer Well-Known Member

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    Hey Serendipity,

    In Quantum Entanglement there is no "event" or physical change, merely a measurement of an existing physical state - one which we can't set beforehand. So my analogy holds true - we don't know what the measurement is until we make it, the nature of making the measurement forces the state - the particle at the other end always had the same state - it just wasn't measured! Spooky action at a distance!

    Ok with regards to the Alcubierre drive - my original criticism still stands. The Alcubierre "drive" is an idea based on solutions to Einsteins field equations, the solutions are mathematically consistent BUT in order for them to work they need a form of negative matter - now this is a form of exotic matter that we don't even know exists, indeed we don't know if it is even possible for this matter to exist. Lets just say that this matter does exist - it doesn't preclude a physical mechanism that can deliver on the solutions to the field equations. The solutions also ignore QUANTUM properties - which is a given granting that Quantum and Standard physics aren't unified. So it may be that once more work is done unifying Gravity with QE that the solutions then become unworkable.

    Phew - that was fun :)
     
  13. Cathbad

    Cathbad Level 30 Geek Master

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    I'm no longer convinced we're limited to the Speed of Light. Wasn't it just a few years ago they discovered particle that moved at near light speed (thinking at first it had went faster than)? And now they've taken a step toward teleportation.

    Seems to me, given enough time, man has shown he can do virtually anything.
     
  14. Vertigo

    Vertigo Mad Mountain Man

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    The one thing we can never do though is break the rules of physics. Of course we don't yet know all the rules of physics but ultimately if the speed of light is proven to be a physical limit then, no matter how much time we have or how clever we are we can never do the impossible.

    Don't be misled by that teleportation word being used. Quantum teleportation bears no resemblance to anything we would normally call teleportation. In other words we have not taken any steps towards teleporting a physical object from one place to another. I think it's really irritating that the scientist are using the word teleportation in this context.
     
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  15. Cathbad

    Cathbad Level 30 Geek Master

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    Oh, I agree. But I do think it is a step in the direction of.
     
  16. Mirannan

    Mirannan Well-Known Member

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    Further to all this, Harold White of NASA has been working on a modified warp drive that brings down the mass requirement substantially (putting it mildly!) from about the mass of Jupiter to a tonne or so. In fact, preliminary experiments are already being done. Yes, warp field experiments being done right now.

    As if that wan't enough, the same group is also working on a reactionless drive using quantum vacuum energy. Link: Quantum vacuum thruster
     
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  17. SilentRoamer

    SilentRoamer Well-Known Member

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    Light speed isn't just some arbitrary speed though, the constant C is found in lots and lots of physics. It is a physical constraint and the limit at which information can be exchanged. Anything sub-light, even if it is near lightspeed is still sub light. In theory you can accelerate something to 99.99 C, but the energy requirements to make something physical move at C are infinite. So near lightspeed is absolutely within the realm of physics.

    I also believe intellect can accomplish anything, anything within the realm of physics and I suspect physical laws (at least some) to be inviolate. An example of this for me is the Second Law of Thermodynamics.

    @Mirannan I find the idea of a Quantum thruster very appealing for future space travel. The warp drive still depends on matter we don't even know exists, so bringing the energy requirement down is irrelevant if we can't produce negative mass exotic matter.
     
  18. Cathbad

    Cathbad Level 30 Geek Master

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    There was no way we could fly - according to the physics of the time.

    There was no way an iron ship could float - according to the physics of the time.

    Every generation seems to have believed their knowledge of physics was the end-all-get-all... the Final Word.

    And apparently, we're still just as arrogant.
     
  19. Vertigo

    Vertigo Mad Mountain Man

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    I'm not sure that is quite accurate I think all lot of uneducated people might have said those things at one time but I'm not too sure all that many scientists did; da Vinci certainly believed we could do the former and Archimedes pretty much proved the latter. Science back then had a lot of ideas that hadn't been subjected to the scientific method (because that hadn't really been formulated) and so a lot of their ideas were never more than unproven theories. Our current set of theories make many predictions which so far are proving very robust, sufficiently so to believe they are at least getting close to the truth. I don't think any scientists are so arrogant as to believe we have reached the final truth but each iteration is getting closer. It is theoretically possible that a completely new branch of physics might yet come along and turn everything completely on it's head but I think it unlikely that anything as fundamental as the speed of light in vacuum is going to be overturned, there are just so many tested predictions that are based on it. As @SilentRoamer so neatly stated above: "we do have the best understanding of physics we have ever had and the invariable speed of light is a constant that appears to hold true over the entirety of the Observable Universe." I don't think this is arrogance but just pragmatism based on observation.

    It's a bit like Moore's Law which, of course is not a law and has more recently been 'failing'. Eventually we start hitting physical limits and we can't keep gong faster, smaller etc. for ever.

    But of course we cannot predict the future. I just think the weight of probability is massively against it.
     
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  20. Cathbad

    Cathbad Level 30 Geek Master

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    da Vinci was an artist, not a physicist.

    An artist's mind is often more accepting of possibilities than most scientists. And they - including writers - have been the very reasons for science stretching its boundaries.

    And... are you sure "pragmatism" isn't just an excuse for "arrogance"?

    Just askin...

    At 60, I can honestly say that I have learned that "Absolutes" are bound to change.
     
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