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  1. Subscribersonhouse
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    07 Mar '19 01:391 edit
    https://phys.org/news/2019-03-ion-aces-quantum-scrambling.html

    I imagine this won't happen for a few months😉

    BTW, the article says the sun mass black hole will evaporate in 1067 years. They should have paid a bit more attention to the exponent, really 10 to the 67 power years, just a bit longer than the age of the universe as they said. Unless the dude was a young Earther😉
  2. Subscribersonhouse
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    07 Mar '19 05:27
    @sonhouse
    So if such an experiment were actually carried out, presumably a thousand years from now when we can get close enough to a real black hole to do such experiments, isn't the rationale suggesting there may be ways to transmit information faster than the speed of light by being very sneaky with your use of qbits?
  3. Standard memberDeepThought
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    07 Mar '19 14:23
    @sonhouse said
    @sonhouse
    So if such an experiment were actually carried out, presumably a thousand years from now when we can get close enough to a real black hole to do such experiments, isn't the rationale suggesting there may be ways to transmit information faster than the speed of light by being very sneaky with your use of qbits?
    If you had a machine that could send information faster than light then you'd have a machine that could send it back in time. You could use the backwards in time signal to deactivate the machine just before the signal is sent. The machine would be perfect in the sense that its failure modes would be more or less indistinguishable from its normal operation.
  4. Subscribersonhouse
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    09 Mar '19 12:42
    @DeepThought
    How does it follow a faster than c system could send signals backwards in time?

    If say we have a station on Mars, say 15 light minutes away and we can send signals back and forth from Mars to Earth say in one microsecond, how does that indicate the possibility of sending signals back in time? Would the speed of transmission have to be zero time or some such? I would think sending a signal backwards in time would have you getting the signal before it was sent but if all you are doing is sending the signal faster than c at some multiple of c then time would pass before the signal got to the receiver and I don't see how that implies going backwards in time since the signal is still progressing from a past to a future time and not the other way.
    What am I missing?
  5. Standard memberDeepThought
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    09 Mar '19 17:09
    @sonhouse said
    @DeepThought
    How does it follow a faster than c system could send signals backwards in time?

    If say we have a station on Mars, say 15 light minutes away and we can send signals back and forth from Mars to Earth say in one microsecond, how does that indicate the possibility of sending signals back in time? Would the speed of transmission have to be zero time or some such? ...[text shortened]... signal is still progressing from a past to a future time and not the other way.
    What am I missing?
    The ordering of events in Relativity is frame dependent if the separation between the events is space-like. So if you send a faster than light signal between two events with a space-like separation then there is an observer for whom the time of signal arrival was before the signal was sent. Faster than light signals are acausal.
  6. Subscribersonhouse
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    09 Mar '19 18:07
    @DeepThought
    This is hard to wrap my poor mind around. What is 'space LIKE'? What does that mean? Space-like as apposed to space UNlike, not sure where this is leading.
  7. Standard memberDeepThought
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    09 Mar '19 19:12
    @sonhouse said
    @DeepThought
    This is hard to wrap my poor mind around. What is 'space LIKE'? What does that mean? Space-like as apposed to space UNlike, not sure where this is leading.
    If a signal can get between two events even if it is going slower than light then the separation of the two events is said to be space-like. If only a signal traveling at the speed of light can get between them it is said to be null. If only a faster than light signal could get between them then the separation is said to be space-like.
  8. Subscribersonhouse
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    09 Mar '19 20:09
    @DeepThought
    You mean like the hypothetical tachyons? So space-like is for signals both slower than c and faster than c but not exactly at c?
  9. Standard memberDeepThought
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    10 Mar '19 08:27
    @deepthought said
    If a signal can get between two events even if it is going slower than light then the separation of the two events is said to be space-like. If only a signal traveling at the speed of light can get between them it is said to be null. If only a faster than light signal could get between them then the separation is said to be space-like.
    My earlier post should have read:

    If a signal can get between two events even if it is going slower than light then the separation of the two events is said to be time-like. If only a signal traveling at the speed of light can get between them it is said to be null. If only a faster than light signal could get between them then the separation is said to be space-like.
  10. Standard memberDeepThought
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    10 Mar '19 09:111 edit
    @sonhouse said
    @DeepThought
    You mean like the hypothetical tachyons? So space-like is for signals both slower than c and faster than c but not exactly at c?
    That was a typo. The point is that the sign of x^2 - c^2 t^2 determines whether two events have a space- or time-like separation. This quantity, or rather its square root, is called the interval and is the same in all inertial frames of reference. Suppose two events are simultaneous in some frame and separated by a distance L. Then the interval is the same as the distance in that frame. Two observers moving at speed v in opposite directions along the line joining the two events will disagree as to the order the events happened. If the forward moving observer sees the first event at t=-T/2 and x=-a/2 and the second event at t=+T/2 and x=+a/2. Because the interval between two events is the same for all observers we have that:

    L^2 = a^2 - c^2 T^2

    so:

    T = +/- sqrt(L^2 - a^2)/c

    Since a is determined by length dilation it is the same for both the forward and backward moving observers. Each observer sees the reflection of what the other observed so they disagree on the ordering of events.
  11. Subscribersonhouse
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    10 Mar '19 13:04
    @DeepThought
    This is from Einstein? Also, what is 'a' in those equations? I think I am sort of starting to understand.
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