http://www.spiegel.de/panorama/bh-aus-mittelalter-archaeologen-finden-buestenhalter-in-tiroler-schloss-a-845349.html ]]>

Achieving a low tau or equivalently a large relativistic gamma factor (note that this use of “tau” isn’t quite standard terminology though it was used in the classic science fiction novel *Tau Zero*, so I prefer to use gamma) is not “impossible”, just very difficult and again requiring a pretty advanced civilization (though not quite as advanced as building wormholes, I think). With an engine of ideal efficiency in converting fuel mass to kinetic energy in the form of photons (like an ideal matter/antimatter drive), an equation at the bottom of the relativistic rocket page shows that if you accelerate continuously to your destination, the ratio of fuel mass to payload mass will be given by M/m = gamma*(1 + v/c) – 1. Since gamma = 1/sqrt[1 - v^2/c^2], v/c = sqrt[1 - (1/gamma^2)]. So for to achieve gamma=100 (at which point you would be aging 100 times slower than observers on Earth, as measured in Earth’s frame), you would need a ratio of fuel mass to payload mass of 100*(1 + sqrt[1 - (1/100^2)]) – 1, plugging that into the calculator here gives a final result of about 199 times more fuel mass than payload mass (if you want to calculate the fuel:payload needed for different values of gamma, just replace “100″ in the above expression with some other number and copy and past the equation into the online calculator). Of course if you wanted to turn around and return to Earth more fuel would be needed, but our hypothetical advanced civilization might have a refueling outpost at the turnaround location, and it’s also been suggested that a bussard ramjet could be used for braking with respect to the interstellar medium (though the original idea of using a ramjet to continuously accelerate relative to the interstellar medium, as in *Tau Zero*, seems to be unworkable), so you wouldn’t necessarily need to carry fuel for slowing down. There are also some suggestions for how you could accelerate to relativistic speeds in the Earth’s frame without actually needing to carry fuel on board the craft, like the idea of a ship with a giant sail or pusher plate that is pushed along by the beam from a powerful laser in the solar system, or a beam of microscopic pellets accelerated to relativistic speed by something like a giant mass driver. Another idea is that the bussard ramjet could actually be used for increasing speed if it didn’t have to react with the natural interstellar medium, but instead could travel along a trajectory that had been pre-seeded with fuel pellets. See this post and this one at the “Centauri Dreams” blog for some details on these proposed methods, or pages 136-148 of the book Centauri Dreams (available on google books).

Though these sorts of technologies are not as advanced as wormholes, still I would imagine that if we ever manage to achieve them, by that time “we” will no longer be biological humans but rather mind uploads or some other form of AI. And in that case, the whole idea of using relativistic velocities for “forward time travel” will be kind of a moot point, since a computer-based intelligence can achieve the same subjective effect just by slowing the speed of the simulation relative to realtime. Obviously relativistic travel would still be useful for exploring the universe in reasonable amounts of time, though.

]]>Mass: achieving a low tau is impossible. Not enough energy to apply.

]]>Your notion of Mach’s principle is far too vague, it isn’t just about gravity “influencing what happens locally” (if it were, then Newtonian gravity would satisfy Mach’s principle, but it clearly doesn’t), it’s about all acceleration-based effects (such as the centrifugal force felt in a rotating frame of reference) existing *solely* because of acceleration relative to distant masses. General relativity says that if you had a universe which was totally devoid of matter save for a single bucket filled with water, the water would remain flat if the bucket weren’t rotating, but would bulge out if it were. So, most physicists say that general relativity does not perfectly satisfy Mach’s principle.

*Second, it assumes that line cones are always perfect. True when you are dealing with only constant velocities but when you throw acceleration into the mix, they’re only perfect cones at the observer. When you move away from the observer, they become distorted.*

The past light cone of an event E is a perfectly well-*defined* notion (it’s the set of all points in spacetime that could send a signal moving at the speed of light or slower that would reach E) regardless of its shape, there is no assumption in general relativity (or on the page I linked to) that light cones would be “perfect” in the sense of having nice straight sides (which I assume is what you mean by “perfect”). Perhaps you are referring to the diagram on the page I linked to that illustrates light cones with straight sides, but it’s just a schematic intended to show the angle of the light cone in the immediate vicinity of the point on the tip, a common convention in general relativity diagrams (seen in many diagrams in the most famous GR textbook, “Gravitation” by Misner/Thorne/Wheeler).

*You cannot use them in general relativity because they do not account for the variable bending of space.*

Again, nothing in the definition of a “light cone” requires that the sides look like straight lines, and light cones are widely used in general relativity. Why would you make such confident statements dismissing something a physicist wrote about an area of physics you clearly haven’t made any technical study of? Beware the unskilled and unaware trap of overconfidence in your own judgments about a subject you are fairly ignorant of…

* Physicists have a hard time believing that general relativity causes the expansion of the universe. Anything more complex than that is bound to be full of errors.*

Huh? Physicists today have no particular problem believing in general relativity’s prediction of an expanding universe. But in any case, that’s a real-world question about whether the actual universe matches up with the predictions of the theory. The question of whether general relativity *theoretically* allows for closed timelike curves is a purely mathematical one that doesn’t depend on whether you believe the theory is actually correct in the real world. (as I said, no one believes that our universe is a rotating one!) Godel discovered the possibility of closed timelike curves in GR in 1949, and the calculations have not been challenged by any mainstream physicists or mathematicians for all this time, are you seriously suggesting that all of them could be making a mathematical error in their calculations of what is allowed theoretically in general relativity, and that you are qualified to judge them all wrong even though you have no detailed technical understanding of the subject?

But I’m not surprised by this. Physicists have a hard time believing that general relativity causes the expansion of the universe. Anything more complex than that is bound to be full of errors.

]]>Since you cannot understand my postings I trust you understand I cannot understand yours.

Time Line:- The ONLY concept of time we have is the rate at which ‘time’ flows. This we measure by comparison with physical devices, clocks, oscillations, wavelengths. All of these are governed by the proximity to Mass.

SO, at the big bang no one can possible conjecture what time scale was involved.

Simultaneity:- If I perform an action in one room and a friend performs an identical action in another room, one problem is the ’trigger’ which synchronised the two events also, since the rate at which time ‘flows’ varies from one location to another, time dilation dictates the two events would not continue in synchronism. Similarly, if a third party performed the same action on the other side of the world, then the speed of light limits the accuracy of initial synchronisation. Taking the action several light years away would clearly make any notion of initial synchronisation impossible. HOWEVER, this does not mean that all actions, wherever performed, could NOT initially occur simultaneously anyway, whatever the rate at which the actions proceeded. The NOW of time.

Schroedinger’s Cat experiment is erroneously thought to confirm his views on the uncertainty of events, but has been wrongly translated. Even he was sceptical of deductions made in quantum theory. I think it has been forgotten that he proposed that matter was standing waves, in which case precise location of place and time allocated to any ‘particle’ would be impossible.

Similarly, Maxwell suspected ‘particles’ were vortices in the Aether. An idea he eventually disregarded.

I’m not expecting you to agree with me, but I don’t propose to continue with this posting. When the Higgs field is proved to be a non-starter, perhaps we can continue with the Wave Theory of Matter. This will eventually explain how photons are transmitted via matter waves, hence the dependence of the speed of light on adjacent mass, and why Gravity is simply the refraction of the Matter Wave as predicted by Einstein as Space Time bending or warping. ]]>

Aw crap. Wrong thread. My bad.

]]>No, but relativity says that it would be impossible in principle to find any empirical evidence for a single unique “Now”–either relativity is wrong about the laws of physics being identical in different inertial frames, *or* the notion of a “common Now” must be a purely metaphysical one that believers take on faith. Do you disagree that these are the only two options? If not, are you OK with the idea that the second might be true, and that you can have nothing other than faith to support your view on time?

*A mistake, which has a just little reference to our discussion, is the assumption of a ‘time line’ shortly after the ‘Big bang’. Fractions of seconds are quoted in the instants when ‘time’ would have been impossible to assess, both practically and theoretically, since the measurement of time is relative to the adjacent mass.*

“Impossible to assess” by who? Since there were presumably no sentient beings back then, other quantities like mass and energy and spatial distance would have gone un-assessed too, but this doesn’t seem like a very good argument for their physical nonreality. And I’m not sure what you mean by “the measurement of time is relative to the adjacent mass”–in relativity “relative to” is always used in the context of some quantity (like speed) whose value is defined relative to the coordinate system you’re using (like the different inertial reference frames used by observers moving at constant velocity away from gravity). Are you talking about two different coordinate systems here, one used by an observer standing on a massive object and one used by a distant observer in space or something? If you are, note that proper time is not defined relative to any coordinate system but is a coordinate-invariant quantity, and real physical behaviors, like the half-life for a given particle to decay, are defined in terms of proper time rather than time in given reference frame.

]]>However, Dirac deduced that an high energy Photon (EM wave) produced two particles. The Electron and the Positron.

Matter and anti-matter. Perhaps we can explain dark energy, and hence dark matter, if we consider how electromagnetic waves can combine and then dissociate randomly in ‘empty’ space? I believe this random ‘in’ and ‘out’ of existence is fully within the quantum theories. ]]>

A mistake, which has a just little reference to our discussion, is the assumption of a ‘time line’ shortly after the ‘Big bang’. Fractions of seconds are quoted in the instants when ‘time’ would have been impossible to assess, both practically and theoretically, since the measurement of time is relative to the adjacent mass. (Refraction of a photon passing the Sun). The Michelson Morley experimental results have components of this, in as much as the speed of light is only relative to adjacent Mass, as near a Black Hole. The experiment was originally conceived to investigate Aether drag, but it has the greater value when looked at from the point of view that a component of Matter must carry the Electromagnetic wave. We must remember that ‘particles’ do not exist at a point. They may carry electrostatic and gravitational ‘forces’ and as such their existence radiates out to infinity. ]]>

The Quechua and Aymara see the past in front of them and the future behind them. ]]>

http://www.kowoma.de/en/gps/orbits.htm ]]>

There is evidence of time travel already, and that is our biological past and the path we see in our genetic history in the double-helix through evolution, and by or in our philosophical ‘form’ – but beyond that? Yeah, not really thinking it’s possible. We are HERE now, we will never be THERE, then.

Ya got one chance to live in this philosophical ‘form’, best to live it while you can!

]]>But there’s actually stuff between galaxies. Like photons. Or we wouldn’t be able to see them.

]]>In a black hole or in between the Galaxies there is only “now”. Time dilation, yes. We can only measure ‘time’ by mechanical means. The swing of a pendulum, oscillation of crystal, atomic clocks. All ONLY illustrate the rate at which physical processes ‘occur’ or run, if you must, in a particular inertial frame.

No evidence of wormholes, only speculation derived from mathematics.

They will be saying neutrinos travel faster than the speed of light next! ]]>

Apparently he’s got a new project in the works: http://www.chud.com/70004/breaking-primer-director-shane-carruth-prepping-upstream-color-for-november-start/

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