Author Topic: Theoretical FTL  (Read 26558 times)

Offline colbourne

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Theoretical FTL
« on: 06/23/2008 06:03 AM »
Assumption 1
===========
I am assuming that anti-matter wil be affected by gravity in the reverse to normal matter.

Assumption 2
===========
Therefore if we can create an anti matter object we should be able to accelerate it up to FTL. This in itself should allow FTL communications.

Assumption 3
===========

We can currently contain anti-matter by magnetic means, so we should be able to contain normal matter by a similar means inside our anti-matter spacecraft.

I expect the new CERN accelrator will be able to answer my probably incorrect assumptions.

Offline Eraser

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Re: Theoretical FTL
« Reply #1 on: 06/23/2008 10:08 AM »
No, gravitation equally affects on a matter and an antimatter.

Offline whitewatcher

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Re: Theoretical FTL
« Reply #2 on: 06/23/2008 11:23 AM »
Yep, anti-matter and matter are made of the same thing: energy.

To observe a reverse gravitational effect, you would need something like anti-antimatter (composed of anti-energy).
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Offline William Barton

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Re: Theoretical FTL
« Reply #3 on: 06/23/2008 12:16 PM »
I forget who, but somebody one suggested the force of negative gravity be referred to as "levity."

It's probably not a good idea to try to prognosticate the enabling technologies of soft SF (unless you're a high-end theoretical cosmologist or something). FTL, teleportation, time-travel, etc. do for SF what magic wands and incantations do for fantasy. One of their hallmarks is, they enable secondary technologies that allow us to bypass the secondary (practical) limitations imposed by physics. For example, if you have teleportation, you instantly have fuelless rockets. You sink a transmitter in Jupiter's atmosphere, a receiver at the back end of your spaceship, and la voila! The ignored magic trick is the energy density required for something like teleportation to work. They are all effectively perpetual motion machines, and if you had the command of physics necessary to make them work, you wouldn't need them.

The issue with trying to get past the contraints imposed by physics as we know it is, first you have to get past the contraints imposed by practical engineering. Somebody comes up with a theory that allows FTL, and Step 1 turns out to be, "Accummulate 400 vigintillion tonnes of neutronium and shape it into a rotating torus 4cm in diameter..."

A brilliant example of the borderland of achievable technology was Arthur C. Clarke's black-hole rocket engine in "Imperial Earth."

Offline cpcjr

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Re: Theoretical FTL
« Reply #4 on: 06/23/2008 02:12 PM »
Assumption 1
===========
I am assuming that anti-matter wil be affected by gravity in the reverse to normal matter.

This assumption is wrong anti-matter is affect by gravity the same way ordinary matter is. 

Quote
Assumption 2
===========
Therefore if we can create an anti matter object we should be able to accelerate it up to FTL. This in itself should allow FTL communications.

Wrong even if assumption 1 were correct, which it is not.
1. The Gravity of the sun would only accelerate it to at most 617.5 Km/s
2. Anti-mater would still be limited by relativity to the speed light.

Quote
Assumption 3
===========

We can currently contain anti-matter by magnetic means, so we should be able to contain normal matter by a similar means inside our anti-matter spacecraft.

This does work but getting enough anti-matter for even the most basic anti-matter rocket would be exreamly expensive: over a $100,000,000.00 / ounce.

Offline scienceguy

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Re: Theoretical FTL
« Reply #5 on: 06/23/2008 08:13 PM »
According to this paper

A `warp drive' with more reasonable total energy requirements
Chris Van Den Broeck
Class. Quantum Grav. 16 No 12 (December 1999) 3973-3979

Even if antimatter responded to gravity in an opposite way to matter, you would still need -10^30 kg of it for a warp drive.
e^(pi)i = -1

Offline Martin FL

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Re: Theoretical FTL
« Reply #6 on: 06/23/2008 09:34 PM »
Here's a curveball, but this area of science is all theory, what is there are gaps in the facts and FTL is possible?

Possible, no chance, I should go back to reading about shuttles? ;)
« Last Edit: 06/23/2008 09:34 PM by Martin FL »

Offline scienceguy

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Re: Theoretical FTL
« Reply #7 on: 06/23/2008 11:34 PM »
Miguel Alcubierrre (1994) published a paper that showed that a warp drive is at least mathematically possible, although it would require huge amounts of negative energy. Pfenning and Ford (1997) showed that a warp bubble wall as proposed by Alcubierre would have to be impossibly thin in order to work. Low (1999) showed that a warp in spacetime could travel no faster than the speed of light and that such a warp would require exotic matter (negative energy). Natario (2002) had a little more positive result: he showed that warp drives could be possible in that they wouldn’t need to compress spacetime ahead of themselves and stretch it behind in order to move. Lobo and Visser (2004) most recently published on this and they showed that in order for a warp drive to work, a couple of things need to happen:
1.   The spaceship can’t travel faster than light
2.   The amount of negative energy must be a significant fraction of the mass of the ship.
As I understand it, a spaceship using a warp drive can’t travel faster than light because gravity only travels at the speed of light, and such a ship would be relying on a negative gravitational force generated by the negative energy it is carrying along in its warp of spacetime.

References

The warp drive: hyper-fast travel within general relativity
Miguel Alcubierre
Class. Quantum Grav. 11 No 5 (May 1994) L73-L77

Fundamental limitations on 'warp drive' spacetimes
Francisco S N Lobo and Matt Visser
Class. Quantum Grav. 21 No 24 (21 December 2004) 5871-5892

Speed limits in general relativity
Robert J Low
Class. Quantum Grav. 16 No 2 (February 1999) 543-549

Warp drive with zero expansion
J Natario
Class. Quantum Grav. 19 No 6 (21 March 2002) 1157-1165

The unphysical nature of `warp drive'
M J Pfenning and L H Ford
Class. Quantum Grav. 14 No 7 (July 1997) 1743-1751
e^(pi)i = -1

Online hop

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Re: Theoretical FTL
« Reply #8 on: 06/24/2008 12:29 AM »
No, gravitation equally affects on a matter and an antimatter.
AFAIK, this is current strong consensus of people in the field, but hasn't been verified experimentally yet.

edit:
Not that FTL or antigravity would necessarily follow even if some difference was detected.
« Last Edit: 06/24/2008 12:30 AM by hop »

Offline khallow

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Re: Theoretical FTL
« Reply #9 on: 06/24/2008 04:14 AM »
My take is that if FTL was possible, we'd probably have seen it by now in particle accelerator experiments and supernova observations. High energy events cover a lot of theoretical possibilities. If there were FTL possibilities, one would need to explain why those possibilities aren't been seen in the trillions of recorded collisions by particle accelerators and why we don't see anything precede the neutrino (and sometimes gamma ray) burst from a supernova.

A technology that might be feasible is the wormhole. Mathematically, it's a "handle" or hole in space-time, that provides an alternate path to a destination that isn't equivalent to the usual way of going between two points. In particular, at no time is anything traveling faster than the speed of light. This changes the topology of space which may or may not be possible.

Optimistically, this new path is considerably shorter than the usual one. For example, Alpha Centauri is 4+ light years away from Earth. A wormhole might provide an alternate path that is say 20 AU long instead. That might be useful merely for communication (under six hours round trip communication time) or even for travel if the hole can be made wide enough (and the environment inside the wormhole is survivable for a vehicle).

As I understand it, the two ends of the wormhole would be created next to one another. Each end would go to an appropriate destination. I have no idea how you'd move it around, keep it from pinching shut, or change its length.
Karl Hallowell

Offline TyMoore

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Re: Theoretical FTL
« Reply #10 on: 06/24/2008 03:43 PM »
Miguel Alcubierre's "Warp Metric" relies on the bizarre behavior that a negative energy mass and a positive energy mass will have for each other: the positive mass attracts the negative mass, but the negative mass repels the positive mass. Or more correctly, the positive mass has the usual gravity field, but the negative mass has a gravity field with a negative sense (as felt by the positive mass.) So a system composed of two equal magnitude but opposite sensed masses (total energy of system: zero) will accelerate in the direction of the positive mass.

Miguel Alcubierre took the idea to the extreme by positing large masses: neutronium density or more. Further he used a nifty little gravitational trick: the gravity field inside a spherically symmetric shell of mass is zero--in general relativity terms, the spacetime inside a spherical shell is approximately flat. So putting the two ideas together you get a spherical shell with the forward end composed of positive energy matter, the aft half is composed of negative energy matter, and the 'vessel' or transport is at the center of the shell in the flat spacetime 'island' in the middle. Increase the density of the shell until it comes close to the density of neutronium, and voila you have massive acceleration that the occupants inside won't feel (they're in free fall.)

The system does not appear to violate conservation of energy as long as the spherical shell has a net-zero energy (sum of the positive energy mass and negative energy mass is zero;) the vessel inside does not possess any more or less kinetic energy than what it started out with since the 'spacelike' FTL movement is similar in some regards to expansion of the early universe.

This is what I got out of Mr. Alcubierre's paper (without being able to do the General Relativistic Tensor mathematics involved in the transforms!)

Offline gospacex

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Re: Theoretical FTL
« Reply #11 on: 06/24/2008 04:21 PM »
Further he used a nifty little gravitational trick: the gravity field inside a spherically symmetric shell of mass is zero--in general relativity terms, the spacetime inside a spherical shell is approximately flat. So putting the two ideas together you get a spherical shell with the forward end composed of positive energy matter, the aft half is composed of negative energy matter,

Well, spherical shell's interior has zero gravity field _only if_ the density and thickness of the shell is the same eveywhere. The above description seems to violate that.

Offline colbourne

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Re: Theoretical FTL
« Reply #12 on: 06/26/2008 02:18 AM »
If anti-matter did respond to gravity differently to normal matter one of the results might have been after the big bang all the anti-matter would have quickly accelerated away at faster than light speed which may explain why there appears to be an absence/shortage of anti-matter in the universe.

This space craft seems expensive but as with everything you get what you pay for. I would say it is a bargain if it really could be built !!!

Initially once we get some results proving how gravity and anti-matter are linked , it might be a useful study for the SETI people.

If my assumptions were correct could we build a communications device that would work ?

Online hop

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Re: Theoretical FTL
« Reply #13 on: 06/26/2008 02:56 AM »
If anti-matter did respond to gravity differently to normal matter one of the results might have been after the big bang all the anti-matter would have quickly accelerated away at faster than light speed which may explain why there appears to be an absence/shortage of anti-matter in the universe.
No, as previously pointed out, even if antimatter doesn't respond as we expect to gravity (which itself would be a huge surprise) that doesn't imply FTL.

Offline Suzy

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Re: Theoretical FTL
« Reply #14 on: 06/26/2008 06:11 AM »
As I understand it (not being a physicist!), you can't go Faster-than-light at all, but there are ways around this (in science fiction, at least!). One as mentioned is to use a wormhole. Two points in space are brought together and a hole is poked through spacetime, and the starship just pops through without traversing any distance in real space. (If anyone saw the movie Event Horizon there is a scene where Sam Neil explains this with a piece of paper and a pencil). A wormhole is a hole, not a tunnel (as incorrectly depicted in some sci-fi films).

A similar concept is folding space - I am not sure if it is the same as a wormhole - where a starship pulls or warps space toward it until it reaches the place it wants to be (without actually moving itself physically).

My take is that if FTL was possible, we'd probably have seen it by now in particle accelerator experiments and supernova observations. High energy events cover a lot of theoretical possibilities. If there were FTL possibilities, one would need to explain why those possibilities aren't been seen in the trillions of recorded collisions by particle accelerators and why we don't see anything precede the neutrino (and sometimes gamma ray) burst from a supernova.

A technology that might be feasible is the wormhole. Mathematically, it's a "handle" or hole in space-time, that provides an alternate path to a destination that isn't equivalent to the usual way of going between two points. In particular, at no time is anything traveling faster than the speed of light. This changes the topology of space which may or may not be possible.

Optimistically, this new path is considerably shorter than the usual one. For example, Alpha Centauri is 4+ light years away from Earth. A wormhole might provide an alternate path that is say 20 AU long instead. That might be useful merely for communication (under six hours round trip communication time) or even for travel if the hole can be made wide enough (and the environment inside the wormhole is survivable for a vehicle).

As I understand it, the two ends of the wormhole would be created next to one another. Each end would go to an appropriate destination. I have no idea how you'd move it around, keep it from pinching shut, or change its length.

« Last Edit: 06/26/2008 06:13 AM by Suzy »

Offline Lampyridae

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Re: Theoretical FTL
« Reply #15 on: 06/26/2008 06:37 AM »
I forget who, but somebody one suggested the force of negative gravity be referred to as "levity."

It's probably not a good idea to try to prognosticate the enabling technologies of soft SF (unless you're a high-end theoretical cosmologist or something). FTL, teleportation, time-travel, etc. do for SF what magic wands and incantations do for fantasy. One of their hallmarks is, they enable secondary technologies that allow us to bypass the secondary (practical) limitations imposed by physics. For example, if you have teleportation, you instantly have fuelless rockets. You sink a transmitter in Jupiter's atmosphere, a receiver at the back end of your spaceship, and la voila! The ignored magic trick is the energy density required for something like teleportation to work. They are all effectively perpetual motion machines, and if you had the command of physics necessary to make them work, you wouldn't need them.

The issue with trying to get past the contraints imposed by physics as we know it is, first you have to get past the contraints imposed by practical engineering. Somebody comes up with a theory that allows FTL, and Step 1 turns out to be, "Accummulate 400 vigintillion tonnes of neutronium and shape it into a rotating torus 4cm in diameter..."

A brilliant example of the borderland of achievable technology was Arthur C. Clarke's black-hole rocket engine in "Imperial Earth."

A classic thought experiment exists on the teleportation idea. Drill a hole through the Earth (yes, yes, I know...), evacuate it and drop an object down it. It will travel down, pop up in Australia or wherever the exit is, allowing you to catch it. Zero energy is required (apart from the catch) so in effect you have teleportation for nothing (after drilling the hole through Earth...).

It's a way of using potential energy to move something, and not actually pay the gazillion dollar energy bill. So it may therefore be possible to use potential energies such as casimir effect (which theoretically can only be tapped once, like dropping a ball is for gravitational potential) and using it for whatever purpose. I don't believe we will manipulate gazillion tonnes of neutronium anytime soon but the ability to manipulate if not harvest quantum effects might give you would give you options into these FTL options.

As for FTL itself, nothing prevents you travelling faster than light (in special relativity), it just prevents you from accelerating past the lightspeed barrier. Decelerating from FTL is also bad; you re-enter normal space as a blinding cascade of Cherenkov radiation... but then again wasn't it Stephen Hawking who made that bet about "information never being able to leave a black hole?"

A lot of basic assumptions have been spectacularly demolished over recent years, and have been replaced by "erm, we don't know." Case in point, the inflationary universe. So our standard physics models may be due for updates soon. It's the nature of science.
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Offline scienceguy

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Re: Theoretical FTL
« Reply #16 on: 06/27/2008 07:48 PM »
Let's say antimatter responds to gravity in an opposite manner to matter. Would it be cheaper to harvest it from Jupiter's radiation belts or dedicate a single particle accelerator to make it?
e^(pi)i = -1

Offline khallow

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Re: Theoretical FTL
« Reply #17 on: 06/29/2008 07:48 AM »
Probably neither. It'd probably be easier to build a large scale solar powered plant in close orbit around the Sun (say a few million kilometers out or less) and farm the solar wind.
Karl Hallowell

Offline Suzy

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Re: Theoretical FTL
« Reply #18 on: 07/08/2008 08:28 AM »
...A brilliant example of the borderland of achievable technology was Arthur C. Clarke's black-hole rocket engine in "Imperial Earth."

An explanation of the Asymptotic Drive (from here):

The main character takes a trip from the Saturnian moon of Titan to Earth in a vessel powered by the “Asymptotic Drive” which is basically a small mass black hole (in the book it was one with “one or two thousand tons mass” – something which would be proton-sized or thereabouts) suspended in a very powerful magnetic field. The way it works is like this: The black hole “eats” matter as we all know, but it can only consume matter at a set rate depending on its mass and the size of the Event Horizon which surrounds the singularity. Now, (as Clarke visualizes) you dump a few grams per second of plain hydrogen onto the black hole which attempts to consume all of the hydrogen but can’t so the remaining hydrogen compresses against itself and the event horizon to the point that it gets hot.

Very hot.

Hot enough to fuse.

Now the singularity is suspended via powerful magnetic fields at the end of a tube open at one end to space and the superheated hydrogen jets out of the open end of the tube. This superhot gas is plasma which means it is electrically active and also means it can be shaped, focussed and directed by magnetic fields. The result is one has a fusion powered rocket which creates thrust with a nozzle velocity far in excess of anything a chemically powered rocket could produce, and do it for weeks on end. In the book, the billion-mile trip from Titan to Earth took 20 days with 10 days accelerating and 10 days decelerating.


You're still stuck going through normal space, though.

In the Event Horizon movie a "black hole drive" was used to somehow fold space so the ship could jump instantly from one point in space to another. Any idea of the details of how that could work?

Online Eerie

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Re: Theoretical FTL
« Reply #19 on: 07/08/2008 01:18 PM »
Suzy, you could just use a fusion rocket, without messing with a HEAVY black hole.

And antimatter rocket would be better anyway.
Quote from: Jim
Wrong.

Offline Suzy

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Re: Theoretical FTL
« Reply #20 on: 07/08/2008 08:42 PM »
Suzy, you could just use a fusion rocket, without messing with a HEAVY black hole.

And antimatter rocket would be better anyway.

But black holes are cooler;D

Offline josh_simonson

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Re: Theoretical FTL
« Reply #21 on: 07/08/2008 11:22 PM »
For conservation of energy to maintained, a wormhole or similar conveyance would require a minimum energy input of the difference in potential and kinetic energy between one and and the other in order to work, or perhaps it'd only be possible to fold space to a point of equal energy.   

Traveling at the speed of light is instantaneous to the traveler, so I suspect that c is effectively infinite speed, and it's just simply a matter of the ways we perceive and measure time and space don't work well at such extremes.  Looking out across the universe, a star 1 light year away is seen as it was one year ago - so the x,y and z coordinates can be viewed as distances in time.  Then c is 1s/s, or just 1 without units and you can't travel faster than 1.  There, now that sounds better than you can't travel faster than ~3e8m/s.

Offline gospacex

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Re: Theoretical FTL
« Reply #22 on: 07/09/2008 08:09 AM »
For conservation of energy to maintained, a wormhole or similar conveyance would require a minimum energy input of the difference in potential and kinetic energy between one and and the other in order to work

Global conservation of energy is not enforced by General Relativity, only local. It is possible to construct a setup where energy is not only not conserved, but where it is impossible to define a notion of "energy" globally.

Quote
Traveling at the speed of light is instantaneous to the traveler, so I suspect that c is effectively infinite speed, and it's just simply a matter of the ways we perceive and measure time and space don't work well at such extremes.  Looking out across the universe, a star 1 light year away is seen as it was one year ago - so the x,y and z coordinates can be viewed as distances in time.  Then c is 1s/s, or just 1 without units and you can't travel faster than 1.  There, now that sounds better than you can't travel faster than ~3e8m/s.

It sounds not better, but bizarre. Reading more on subject of Special Relativity might help you to get a firmer grasp on what's going on. Wikipedia article is not a bad start.

Can't agree on "c is instantaneous", why radar bounces off planets come back with delay?

Time and space are definitely different dimensions, since they enter into equations with opposite signs, like in ds^2 = dt^2 - dx^2 - dy^2 - dz^2.

Online Eerie

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Re: Theoretical FTL
« Reply #23 on: 07/09/2008 01:59 PM »
Can't agree on "c is instantaneous", why radar bounces off planets come back with delay?

C is instantaneous from POV of the traveller. But you will have to be massless.
Quote from: Jim
Wrong.

Offline Suzy

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Re: Theoretical FTL
« Reply #24 on: 07/29/2008 05:39 AM »
Discovery.com article, 28/7: "Warp Drive Engine Would Travel Faster Than Light".

Offline TyMoore

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Re: Theoretical FTL
« Reply #25 on: 07/29/2008 03:48 PM »
With regards to using blackholes as power sources. A 1000 metric ton black hole will evaporate by Hawking Radiation in less than a microsecond. You'd get a very big bang, but little propulsion!

If you go smaller, much smaller: milligram mass blackholes, and you make them dozens of times a second, then the emissions should be predominantly gamma-rays, and electron/positron pairs, which will annhilate to gamma-rays. Use the gamma-rays to impinge on something dense, like tungsten balls in a pressure vessel and nozzle: you have something akin to a nuclear thermal rocket. Or you could use a closed Brayton cycle and use the electricity to power conventional ion thrusters.

Or if you really want to go wild, why not use the intense gamma-rays to heat something else: like lunar regolith and use that as your working fluid! Who cares if its inefficient from Isp point of view: with enough gamma-rays the plasma will be at tens of millions of degrees anyway. And the drive flare should be visible all the way across the solar system. Cool!
« Last Edit: 07/29/2008 03:50 PM by TyMoore »

Offline ChevalierGuard

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Re: Theoretical FTL
« Reply #26 on: 07/29/2008 11:05 PM »
Kaluza Klein Theory...

CG

Offline khallow

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Re: Theoretical FTL
« Reply #27 on: 07/29/2008 11:43 PM »
Kaluza Klein Theory...

What about Kaluza Klein theory? As far as I know, it's the idea that you can start with a higher dimension massless/pure geometry model and reduce by the extra dimensions to get a model with our observed spacetime and physical properties like mass/energy (including curvature and possibly a cosmological constant or "dark energy") or electric current flows.
« Last Edit: 07/29/2008 11:46 PM by khallow »
Karl Hallowell

Offline ChevalierGuard

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Re: Theoretical FTL
« Reply #28 on: 07/30/2008 10:23 PM »
Kaluza klein theory...

Not exactly...as far as I know the equations don't show dark energy or matter..

However, there is a compactification.. but primarily it links gravity equations to EM... and vice versa.. 
I speaking of the 5D case of course.. the other stuff really is nonsense.
speaking of the 11 dimensions..

Not to bore with equations, here is a simple definition from wikpedia..

In physics, Kaluza–Klein theory (or KK theory, for short) is a model that seeks to unify the two fundamental forces of gravitation and electromagnetism. The theory was first published in 1921 and was discovered by the mathematician Theodor Kaluza who extended general relativity to a five-dimensional spacetime. The resulting equations can be separated out into further sets of equations, one of which is equivalent to Einstein field equations, another set equivalent to Maxwell's equations for the electromagnetic field and the final part an extra scalar field now termed the "radion".

This is part of the solution...

Nice chatting with you...

Wish NASA would give pic EM and Beamline and Klystron codes freely.  You could do alot with a small Linux cluster..

Nice chatting..

CG






Offline colbourne

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Re: Theoretical FTL
« Reply #29 on: 08/01/2008 07:28 AM »
This weeks New Scientist (1 August 2008) has an article about how antimatter particles sometimes bounce off normal matter.
This possibly supports my previous assumption about the possible anti-gravity that might occur with anti-matter.

http://www.newscientist.com/channel/fundamentals/mg19926674.600-antimatter-plus-matter-doesnt-always-equal-bang.html

The "Colbourne" drive still might work. I expect we will know soon.


Offline gospacex

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Re: Theoretical FTL
« Reply #30 on: 08/01/2008 10:35 AM »
This weeks New Scientist (1 August 2008) has an article about how antimatter particles sometimes bounce off normal matter.

I think proton/antiproton collision was never thought to 100% reliably result in annihilation, they may just scatter on each other.

Quote
This possibly supports my previous assumption about the possible anti-gravity that might occur with anti-matter.

Magnitude of gravitational interaction in proton-antiproton (or proton-proton) pair is on the order of 10^37 times weaker than electromagnetic. Likely not detectable.

Offline khallow

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Re: Theoretical FTL
« Reply #31 on: 08/01/2008 05:47 PM »
Kaluza klein theory...

Not exactly...as far as I know the equations don't show dark energy or matter..

However, there is a compactification.. but primarily it links gravity equations to EM... and vice versa.. 
I speaking of the 5D case of course.. the other stuff really is nonsense.
speaking of the 11 dimensions..

If you instead contract (collapse the direction in question) a 5 dimensional space (4 spatial/1 time dimensions) along a radial direction rather than along a single spatial dimention, you can get de Siter and anti-de Siter spaces. The idea is to treat each ray coming from the origin as a point in a 4 dimensional space. If this were a regular 5 dimensional Euclidean space, the result is a sphere centered at the origin (each ray passes once through this sphere). With one timelike dimension, you end up with a hyperboloid sheet instead (again each ray passing once through the sheet). The cosmological constant shows up as the inverse of a "radius" of this sheet.

Also, given that we observe a strong and weak force, this encourages the consideration of higher dimensional models. They may have limited physical relevance, but it is a good way to generate potential models for the interaction of the four forces and the math might be applicable to a better model. That is, it might turn out that a "good" model has a 10, 11, 26, etc dimensional extension that simplifies the math of the original model. You just need to know how to go from the manipulations of the higher dimension space to the real world space.
Karl Hallowell

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Re: Theoretical FTL
« Reply #32 on: 08/02/2008 07:35 AM »


Miguel Alcubierre took the idea to the extreme by positing large masses: neutronium density or more. Further he used a nifty little gravitational trick: the gravity field inside a spherically symmetric shell of mass is zero--in general relativity terms, the spacetime inside a spherical shell is approximately flat. So putting the two ideas together you get a spherical shell with the forward end composed of positive energy matter, the aft half is composed of negative energy matter, and the 'vessel' or transport is at the center of the shell in the flat spacetime 'island' in the middle. Increase the density of the shell until it comes close to the density of neutronium, and voila you have massive acceleration that the occupants inside won't feel (they're in free fall.)

I wonder if this 'shell' would also act as a 'deflector shield' and/or a 'cloaking device'.  seems to me that something as dense as 'nuetronium' would be damned tough to see thru, if it let any EM radiation thru at all.
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Offline khallow

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Re: Theoretical FTL
« Reply #33 on: 08/02/2008 06:00 PM »
OTOH, everyone who detects the neutronium would suspect you were hiding something. An analogy is a 50 pound lead brick. There are all sorts of tricks for hiding a brick and usually it's not that hard. It's not particularly big and very few people really care about where you go with a lead brick. But don't try to pass one through an airport X ray security system.

Due to the density of the lead brick, you can stick anything in the center and it won't be scannable by X ray machines. But what would be the point? Most circumstances where the shielding matters, the brick itself would raise suspicion. The biggest exception is when the hidden item generates a signal somehow (say because it is a kilogram of plutonium 239).
« Last Edit: 08/02/2008 09:54 PM by khallow »
Karl Hallowell

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Re: Theoretical FTL
« Reply #34 on: 08/03/2008 01:33 AM »
Creation of Mini black holes?

and capturing virtual particles?

any thoughts, known papers, etc?

CG

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Re: Theoretical FTL
« Reply #35 on: 08/03/2008 04:58 AM »
Creation of Mini black holes?

Very small rotating black holes do appear to be promising. I wouldn't recommend doing it on a planet or near a star. But it does look a good way to store energy.

Quote
and capturing virtual particles?

any thoughts, known papers, etc?

My take on virtual particles is that they are artifacts of particular models. For example, quantum electrodynamics (or QED, a quantum field theory used to describe electromagnetism) requires "virtual photons" to adequately describe the interaction between charged particles. Normal photons have two vibration modes (usually called "degrees of freedom") while virtual photons have the full four modes of vibration (sound waves are an example of waves that have four vibration modes). If one uses the QED model and attempts to observe a virtual photon, a strange thing happens. The two modes that we see have the expected positive probability of being observed. But the other two modes have a negative probability of being observed. This leads to the convention that observable states are only the states with positive probability.

Still the talk of black holes and virtual particles does allow for the possibility of gravitational capture of hard to observe particles. For example, any sufficiently dense object (possibly a neutron star just a bit shy of unrestrained collapse) can have a photon sphere. That is, the object through it's deep gravity well can actually trap photons in orbit around the object. Anything moving slower than that will be trapped in higher orbits. One can then attempt to scatter observable stuff off of what is in the photon sphere.
« Last Edit: 08/03/2008 04:59 AM by khallow »
Karl Hallowell

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Re: Theoretical FTL
« Reply #36 on: 08/04/2008 03:02 AM »
Karl,

Thanks for the link Photon sphere link...  I knew of virtual particles (QED based stuff) thought you might have additional info..

Has anyone modeled collisions or merges of mini black holes? Cactus simulations?

I haven't modeled anything astronomical in years..  need to get a Linux cluster up and running...
Recently only working on beamline stuff... O and M devices..

I heard that
Physicists are actually trying to probe other spatial dimensions using particle physics experiments?
True? if so, papers?

thx

CG



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Re: Theoretical FTL
« Reply #37 on: 08/04/2008 09:42 AM »
any sufficiently dense object (possibly a neutron star just a bit shy of unrestrained collapse) can have a photon sphere. That is, the object through it's deep gravity well can actually trap photons in orbit around the object. Anything moving slower than that will be trapped in higher orbits. One can then attempt to scatter observable stuff off of what is in the photon sphere.

I don't think so. Photon sphere is not a stable orbit, you can't "accumulate" orbiting photons there. IIRC lowest stable orbit around non-rotating black hole has a radius of 3*Rs.

Offline khallow

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Re: Theoretical FTL
« Reply #38 on: 08/04/2008 10:35 PM »
any sufficiently dense object (possibly a neutron star just a bit shy of unrestrained collapse) can have a photon sphere. That is, the object through it's deep gravity well can actually trap photons in orbit around the object. Anything moving slower than that will be trapped in higher orbits. One can then attempt to scatter observable stuff off of what is in the photon sphere.

I don't think so. Photon sphere is not a stable orbit, you can't "accumulate" orbiting photons there. IIRC lowest stable orbit around non-rotating black hole has a radius of 3*Rs.

I'm not sure I understand what you're saying. This would be an orbit, then you effectively have that photon trapped in this zone. It can still escape either by hitting other things or due to the quantum nature of the photon, tunneling either into the massive object or out of the system.
« Last Edit: 08/04/2008 10:35 PM by khallow »
Karl Hallowell

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Re: Theoretical FTL
« Reply #39 on: 08/05/2008 02:54 AM »
Gentlemen,

Using miniblack holes to capture virtual particles and hence using the miniblackhole as storage device may not be the trick...Remember, Stephen Hawking predicted that black holes eventually evaporate!

Darn that negative energy virtual particle..

CG

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Re: Theoretical FTL
« Reply #40 on: 08/05/2008 08:22 AM »
any sufficiently dense object (possibly a neutron star just a bit shy of unrestrained collapse) can have a photon sphere. That is, the object through it's deep gravity well can actually trap photons in orbit around the object. Anything moving slower than that will be trapped in higher orbits. One can then attempt to scatter observable stuff off of what is in the photon sphere.

I don't think so. Photon sphere is not a stable orbit, you can't "accumulate" orbiting photons there. IIRC lowest stable orbit around non-rotating black hole has a radius of 3*Rs.

I'm not sure I understand what you're saying. This would be an orbit, then you effectively have that photon trapped in this zone. It can still escape either by hitting other things or due to the quantum nature of the photon, tunneling either into the massive object or out of the system.

Stable orbit is an orbit where small perturbations result in small changes of orbit.

The "photon sphere" is not such an orbit, neither any other orbit closer than three Schwarzschild radii. Even though theoretically an object (or photon) with *exactly* the right kinetic energy and direction of flight can be put on these orbit, even tiniest error in speed or direction will change this orbit into a spiral trajectory either falling into the hole or going outward until the object is on orbit >= 3 Rs.

The closest such unstable orbit is at 3/2 Rs and it requires "objects" to have v=c. In other words, only photons can be put on this orbit. But "can be put" is not equal to "there are lots and lots of photons on this orbit". Actually, most of the time (read: always) this orbit is empty.
« Last Edit: 08/05/2008 08:23 AM by gospacex »

Offline sandrot

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Re: Theoretical FTL
« Reply #41 on: 08/13/2008 10:02 PM »
"Paper planes do fly much better than paper spacecrafts."

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Re: Theoretical FTL
« Reply #42 on: 12/04/2011 11:32 AM »
Have we discovered any more about the properties of anti-matter to answer the ideas raised in this thread yet ?


I think it is fair to say that we have more doubt now on the definite limits imposed by Einsteins theories and scientists are willing to speculate on the possibility of FTL.

This thread is also relevant :-

http://forum.nasaspaceflight.com/index.php?topic=24858.0

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Re: Theoretical FTL
« Reply #43 on: 12/04/2011 02:55 PM »
Why don't we prove the characteristics of anti-matter first?  It takes very little thought, and not that much more typing to come up with usefull applications for anti-gravity.
Sometimes I just flat out don't get it.

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Re: Theoretical FTL
« Reply #44 on: 12/04/2011 08:19 PM »
Assumption 1
===========
I am assuming that anti-matter wil be affected by gravity in the reverse to normal matter.

Assumption 2
===========
Therefore if we can create an anti matter object we should be able to accelerate it up to FTL. This in itself should allow FTL communications.

Assumption 3
===========

We can currently contain anti-matter by magnetic means, so we should be able to contain normal matter by a similar means inside our anti-matter spacecraft.

I expect the new CERN accelrator will be able to answer my probably incorrect assumptions.


Nope, basic knowledge will do.

First two are wrong.
Third is irrelevant.
JIMO would have been the first proper spaceship.

Offline colbourne

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Re: Theoretical FTL
« Reply #45 on: 12/04/2011 08:29 PM »
Assumption 1
===========
I am assuming that anti-matter wil be affected by gravity in the reverse to normal matter.

Assumption 2
===========
Therefore if we can create an anti matter object we should be able to accelerate it up to FTL. This in itself should allow FTL communications.

Assumption 3
===========

We can currently contain anti-matter by magnetic means, so we should be able to contain normal matter by a similar means inside our anti-matter spacecraft.

I expect the new CERN accelrator will be able to answer my probably incorrect assumptions.


Nope, basic knowledge will do.

First two are wrong.
Third is irrelevant.

How did you know that the first two were wrong ?

Offline Joris

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Re: Theoretical FTL
« Reply #46 on: 12/04/2011 08:37 PM »
How did you know that the first two were wrong ?

Observed since the moment we discovered anti-particles.

An example:
An electron and a positron are antiparticles of each other.
They exhibit perfectly predictable behavior.

Can I ask:
How big is your understanding of physics, it is good to know before continouing this discussion?
JIMO would have been the first proper spaceship.

Offline colbourne

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Re: Theoretical FTL
« Reply #47 on: 12/05/2011 01:15 PM »
How did you know that the first two were wrong ?

Observed since the moment we discovered anti-particles.

An example:
An electron and a positron are antiparticles of each other.
They exhibit perfectly predictable behavior.

Can I ask:
How big is your understanding of physics, it is good to know before continouing this discussion?

I think you better let CERN and other research establishments know, as they are spending a fortune to confirm the properties of anti-matter. As far as I know the exact properties have not been confirmed yet.

I only have a BSc in Physics

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Re: Theoretical FTL
« Reply #48 on: 12/05/2011 01:35 PM »
I think you better let CERN and other research establishments know, as they are spending a fortune to confirm the properties of anti-matter. As far as I know the exact properties have not been confirmed yet.

I only have a BSc in Physics

Oh sure they do, but it is more to check much more subtle things that wether their mass is negative.

We know antimatters charge is reversed (positronium is bound for example), we thus know from electromagnetic effects on antimatter that its inertial mass is positive. We don't strictly know that the gravitational mass is positive, no one has meassured the gravitational mass of antimatter (it is very hard to do), but having positive energy and negative gravitational mass would be very hard to reconcile with general relativity.

Offline KelvinZero

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Re: Theoretical FTL
« Reply #49 on: 12/05/2011 06:07 PM »
Here is a wiki link. Very strongly expected to have the usual gravity though not yet experimentally confirmed.
http://en.m.wikipedia.org/wiki/Gravitational_interaction_of_antimatter

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Re: Theoretical FTL
« Reply #50 on: 12/05/2011 08:15 PM »
Okay fine let us assume anti-matter induces anti-gravity.
This raises a few questions:

A photon is its own antiparticle, how does it act under gravity?

How will particle-antiparticle parirs act under gravity? (charmonium, for example.)

Will an object that has a left side made of antimatter accelarate to the right?

The first one is observed, albeit raises questions about whether gravity is a two component force. (Mass-gravity and energy-gravity.)

The second two are thought-experiments, untill tested, but make me doubt it.


(IMHO, I think that it is best to assume that antimatter acts as predictable as matter with respect to the Standardmodel. At least untill we have an explanation for gravity.)

On a side note: I'm interested what direction you went after getting your BSc in physics: business, research, education, something else?
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Re: Theoretical FTL
« Reply #51 on: 12/05/2011 08:37 PM »
Even this business major knows that gravity is considered to be a function of mass, not of charge.

There is no such thing (so far) as 'antimass'.
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Re: Theoretical FTL
« Reply #52 on: 12/05/2011 09:18 PM »
I am just saying that we have no knowledge of how gravity affects anti-matter and there is thus a possibility that it will act differently to normal matter with gravity. If so it might explain the discrepancy between the amount of matter versus anti-matter in the observed universe (It has simply accelerated away from us and could explain the accelerating expansion of the universe, removing the requirement for dark matter).

I designed visual systems for Singer flight simulators after getting my BSc.

Offline Tass

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Re: Theoretical FTL
« Reply #53 on: 12/06/2011 08:18 AM »
Even this business major knows that gravity is considered to be a function of mass, not of charge.

That is hardly relevant. Antiparticles are not just charge reversed. They are apparently everything-but-mass reversed. Some people speculate that they may be mass reversed as well. You are right there is probably no anti-mass. It is very unlikely, but the premise of this thread is "what if". 

Offline KelvinZero

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Re: Theoretical FTL
« Reply #54 on: 12/06/2011 08:37 AM »
Even this business major knows that gravity is considered to be a function of mass, not of charge.

That is hardly relevant. Antiparticles are not just charge reversed. They are apparently everything-but-mass reversed. Some people speculate that they may be mass reversed as well. You are right there is probably no anti-mass. It is very unlikely, but the premise of this thread is "what if". 

Also many physicists are dedicating themselves to somehow unifying the concepts of gravity and charge. Im probably misusing the terms a bit but that is essentially what the search for the Grand Unified Theory is all about.
http://en.wikipedia.org/wiki/Grand_Unified_Theory

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Re: Theoretical FTL
« Reply #55 on: 12/06/2011 12:53 PM »
Quote from: Colbourne
I think you better let CERN and other research establishments know, as they are spending a fortune to confirm the properties of anti-matter. As far as I know the exact properties have not been confirmed yet.

It is true that all the properties of anti-m have not yet been discovered.  It is your first assumption, made without specific knowledge of the properties, that anti-m would also have anti-g properties.  Since some properties of anti-m are known, it is currently accepted that there is no such thing.  Like Kelvin said; "Very strongly expected to have the usual gravity though not yet experimentally confirmed".

But since, as Tass observes, "the premise of this thread is 'what if'", then one is free, more or less, to talk up the fantastic possibilities of FTL.  It is very easy to do.  Is that all you wish to do?
Sometimes I just flat out don't get it.

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Re: Theoretical FTL
« Reply #56 on: 12/06/2011 03:46 PM »
I will just note that anti-gravity would still not enable faster-than-light.

Negative gravitational and inertial mass would, however, allow you to accelerate without bound.

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Re: Theoretical FTL
« Reply #57 on: 12/06/2011 05:33 PM »
Wouldn't negative mass be both antigravity and negative inertia? I'm thinking of papers by Bondi (1957) and Forward (1990).

Bondi, H. (1957) Negative mass in general relativity. Reviews of Modern Physics 29(3):423-428

Forward, R. L. (1990) Negative matter propulsion. Journal of Propulsion and Power 6(1):28-37
e^(pi)i = -1

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Re: Theoretical FTL
« Reply #58 on: 12/06/2011 05:46 PM »
Oops! I realize the authors in those papers distinguish between negative inertial mass and negative gravitational mass.
e^(pi)i = -1

Offline RanulfC

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Re: Theoretical FTL
« Reply #59 on: 12/06/2011 06:07 PM »
I recall a lot of "speculative-fiction" about anti-matter when it was first discovered/postulated, much of it dealing with the concepts and ideas of what-and-how "contra-terrene" (Cee-Tee was the "popular" name at the time) matter would "interact" with the "standard" universe.

Nothing in the theoretical or observered work indicates "anti-gravity" properties and other than the "mutual-anihilation" aspect antimatter was supposed to simply be a "negativily" charged analog to normal matter. However one rather "glaring" early assumption seems to be "missing" from observed anti-matter phenomon; we don't find mucn (if any) actual "anti-matter" in the universe around us.

The theory (and assumptions) have always been that IF antimatter exists in nature then it SHOULD behave similarly to normal matter in that it SHOULD aggrate together into particles, molecules, and solid representations of "anti-matter"... So the question is where IS the "anti-asteroids," "anti-planets," and "anti-suns" one would expect to find? (Of course one then needs to delve into the exact details of "how" you'd tell the difference barring the catastrophic method of verification :)

Now I'm pretty much expecting my memory is wrong but I seem to recall that a question that has been raised during work on the various things like the "Mach-Effect" and other "alternative" theories on the nature of the universe that struck me was; "We have always pretty much "assumed" that Mass generates gravity, the more mass the higher the gravity. An interesting question though is this: What if mass does NOT 'generate' gravity as we understand it but it is simply that normal matter "concentrates" gravity?"

This leads to the thought that the lack of observed mass' of "anti-iron" etc, might be because anti-matter since it isn't "normal" matter might actually have the opposite effect? Note that this is NOT "anti-gravity" though it's possible it could produce a somewhat similar effect given enough of it, the problem would be since normal matter SEEMS to acumulate due to an increasing mass/increasing gravity in-falling effect, anti-matter would NOT act the same and in fact would be almost impossible for it to accumulate in the "normal" manner.

Thoughts?
(Ok, OTHER than the ones about me being "Crazy" and a "Freak-a-zoid-Nut-Case" Lets concentrate on the "concept" and not my already diagnosed mental issues :) )

Randy
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Offline alexw

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Re: Theoretical FTL
« Reply #60 on: 12/07/2011 03:04 AM »
I recall a lot of "speculative-fiction" about anti-matter when it was first discovered/postulated, much of it dealing with the concepts and ideas of what-and-how "contra-terrene" ...
     You do? That was 1928-1932. How much speculative fiction was written at the time, and were you born circa 1910?
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Offline RanulfC

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Re: Theoretical FTL
« Reply #61 on: 12/07/2011 01:04 PM »
I recall a lot of "speculative-fiction" about anti-matter when it was first discovered/postulated, much of it dealing with the concepts and ideas of what-and-how "contra-terrene" ...
     You do? That was 1928-1932. How much speculative fiction was written at the time, and were you born circa 1910?
    -Alex
Why yes "I do" it's called a "small-town-library" and a good majority of the "Science Fiction" section dated from that period yes :)

But the majority of the stuff I'm thinking of was written around the mid-to-late 40s and beyond.
http://beamjockey.livejournal.com/73304.html

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Randy
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Offline JohnFornaro

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Re: Theoretical FTL
« Reply #62 on: 12/07/2011 02:01 PM »
Dang.  Foiled again!
Sometimes I just flat out don't get it.

Offline colbourne

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Re: Theoretical FTL
« Reply #63 on: 12/21/2016 02:55 AM »
http://www.cbc.ca/news/technology/scientists-measure-antimatter-atom-for-1st-time-1.3903268

"The next phase of the group's experiment, ALPHA-G, will study gravitational forces on antihydrogen, and is expected to take place at the end of 2017. Specifically, the researchers want to see if antihydrogen will "fall up," suggesting that the two repel each other. If it does — which Menary is somewhat skeptical about — it could mean that half the galaxies we see are antimatter galaxies.

The physicists hope that eventually their experiments will provide scientists with yet another piece in the puzzle as to how our universe came to be."

So we should find out whether this will work within a couple of years. As a means of transport I think it is unlikely to ever be of use but it may have potential for use in communications.

Offline Stormbringer

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Re: Theoretical FTL
« Reply #64 on: 12/21/2016 03:01 AM »
there is more articles today related to the above article topic. They have measured the emission spectra for the s1 to p something or the other transition of anti-hydrogen. it is pretty close to the measured spectra for regular hydrogen with the remainder probably down to measurement precision.
When antigravity is outlawed only outlaws will have antigravity.

Offline colbourne

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Re: Theoretical FTL
« Reply #65 on: 02/02/2017 04:12 AM »
http://newatlas.com/dipole-repeller-void-pushing-milky-way/47648/?utm_source=Gizmag+Subscribers&utm_campaign=3a3d9a1e90-UA-2235360-4&utm_medium=email&utm_term=0_65b67362bd-3a3d9a1e90-90223594


Enormous extragalactic void is pushing on the Milky Way. Astronomers have now discovered a huge extragalactic void, called the Dipole Repeller, that's pushing us away.

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Re: Theoretical FTL
« Reply #66 on: 03/23/2017 08:16 PM »

Offline dustinthewind

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Re: Theoretical FTL
« Reply #67 on: 03/24/2017 12:30 AM »
http://newatlas.com/dipole-repeller-void-pushing-milky-way/47648/?utm_source=Gizmag+Subscribers&utm_campaign=3a3d9a1e90-UA-2235360-4&utm_medium=email&utm_term=0_65b67362bd-3a3d9a1e90-90223594


Enormous extragalactic void is pushing on the Milky Way. Astronomers have now discovered a huge extragalactic void, called the Dipole Repeller, that's pushing us away.

I think it might be possible that the dark voids are another universe where gravitational objects what pull in their space expel it out into our universe.  We experience the gravity of this other universe as negative gravity.  This universe may have an excess of anti-matter rather than matter.  Anti-matter possibly being negative energy matter but its time runs backwards.  Negative energy matter already behaves as if its time arrow is backward so reversing time for it makes it behave as if its time arrow runs forward. 

Gravity appears to contract space into it pulling in whats around it.  Think of it as a Lorentz contraction in an accelerating frame.  So if space flows in where does it go?  Into the other universe maybe.  How does their universe perceive our gravity.  As repulsive possibly or as space flowing out which is repulsive to the matter in the other universe as well.  So they perceive us as dark matter and maybe we perceive them as dark matter.  That is they expel space from their dimension into ours and also appear repulsive.  Dipole repulsers.  The only thing different in this universe is because of the dominance of anti-matter time generally runs in reverse but its not a problem because all the matter is negative energy matter so it just behaves like normal matter in reverse time. 

Anyways just some speculation on my part.  Thought you all might find it interesting. 

Offline Spaniard

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Re: Theoretical FTL
« Reply #68 on: 04/05/2017 07:45 AM »
Assuming that antimatter generates antigravity, I think that there is some bad concepts around it. It's not that antimatter was repealed by gravity. It was that antimatter would generate a negative space curvature.
So, the answers to your questions will be the same that the standard model.

It will change other things. For example, photons shouldn't generate space curvature/gravity (never tested as you need a enormous quantity of photons in a small place to "weight" something).
Antimatter would be generate negative curvature, so it will never form planets or stars. Most antimatter would be in intergalactic space. It would generate negative pressure on galaxies.


Offline dustinthewind

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Re: Theoretical FTL
« Reply #69 on: 04/10/2017 01:07 AM »
Assuming that antimatter generates antigravity, I think that there is some bad concepts around it. It's not that antimatter was repealed by gravity. It was that antimatter would generate a negative space curvature.
So, the answers to your questions will be the same that the standard model.

It will change other things. For example, photons shouldn't generate space curvature/gravity (never tested as you need a enormous quantity of photons in a small place to "weight" something).
Antimatter would be generate negative curvature, so it will never form planets or stars. Most antimatter would be in intergalactic space. It would generate negative pressure on galaxies.

No, it is believed anti-matter generates normal gravity as far as I know.  It also takes positive energy to make anti-matter.  What I was speculating is that anti-matter is negative energy in reverse time which makes it behave like normal matter but when it comes into contact with normal matter the time and then energy cancel out inducing a wave in the vacuum which carries the effective mass elsewhere.  This being why when an electron and positron annihilate their mass isn't lost.  It is carried off in the light which is the result of the annihilation. 

The negative gravity speculation was just that, but speculating that dark matter is actually matter in a parallel dimension much like our own.  In this other dimension time runs backward and most matter that exist is anti-matter.  My speculation tries to answer the question - "where did all the anti-matter go?"  You see when we create matter - particles we always create equal amounts of matter+anti-matter.  So where did all this matter come from and where is all the anti-matter.  My speculation indicates maybe it is in a parallel dimension where time is running in reverse and it is considered dark matter to our dimension where it expels space into our dimension. 

Offline MrHollifield

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Re: Theoretical FTL
« Reply #70 on: 05/04/2017 07:55 PM »
I think it might be possible that the dark voids are another universe where gravitational objects what pull in their space expel it out into our universe.

...

Gravity appears to contract space into it pulling in whats around it.

AIUI, gravity is our experience of spacetime contracted by the creation of matter from energy. When the energy in that matter is released, say during fusion in a star, spacetime expands outward, reducing the gravitation of the star. In the dark voids, there are no stars releasing energy, so there could be no expansion generated in the voids. More likely, the spacetime expanding out of the luminous regions with many stars is pushing against these voids to expand the universe.

Offline Bob012345

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Re: Theoretical FTL
« Reply #71 on: 05/08/2017 02:30 PM »
Assuming that antimatter generates antigravity, I think that there is some bad concepts around it. It's not that antimatter was repealed by gravity. It was that antimatter would generate a negative space curvature.
So, the answers to your questions will be the same that the standard model.

It will change other things. For example, photons shouldn't generate space curvature/gravity (never tested as you need a enormous quantity of photons in a small place to "weight" something).
Antimatter would be generate negative curvature, so it will never form planets or stars. Most antimatter would be in intergalactic space. It would generate negative pressure on galaxies.

No, it is believed anti-matter generates normal gravity as far as I know.  It also takes positive energy to make anti-matter.  What I was speculating is that anti-matter is negative energy in reverse time which makes it behave like normal matter but when it comes into contact with normal matter the time and then energy cancel out inducing a wave in the vacuum which carries the effective mass elsewhere.  This being why when an electron and positron annihilate their mass isn't lost.  It is carried off in the light which is the result of the annihilation. 

The negative gravity speculation was just that, but speculating that dark matter is actually matter in a parallel dimension much like our own.  In this other dimension time runs backward and most matter that exist is anti-matter.  My speculation tries to answer the question - "where did all the anti-matter go?"  You see when we create matter - particles we always create equal amounts of matter+anti-matter.  So where did all this matter come from and where is all the anti-matter.  My speculation indicates maybe it is in a parallel dimension where time is running in reverse and it is considered dark matter to our dimension where it expels space into our dimension.


Some think that electrons actually are not affected by gravity. The paper below measures gravitational force as 0.09mg. The authors though interpret that there is an induced electromagnetic force in the apparatus that counters gravity but others disagree with that interpretation.

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.19.1049


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