This question has been asked so often (along with the variant why is
AI considered possible but not FTL) that we decided to dedicate a
separate FAQs page to it.
Note that the arguments on this page pertain to a hard science setting based on a
causal relativistic physical universe.
In no way are we saying you can't have FTL in your universe, or in your
favourite Sci Fi scenario; nor are we criticizing other science fiction
franchises or universes that do incorporate FTL. These FAQs are written
to answer questions or criticisms levelled against the OA scenario as
regards our stand on this matter.
Why is there no FTL in the OA Universe?
Why do you allow wormholes, and the exotic
materials used to create them, but do not allow FTL or even
“hyperspace”?
Why do you allow wormholes, but not warp drive? Both
are possible with exotic matter.
With warp drive you never leave your own light cone, so
why do you say that a warp drive will create a paradox?
Why can't you use clarketech for FTL?
Why not use quantum entanglement to create an FTL
communication system?
Why not explain FTL in terms of imaginary mass?
Why is there no FTL in the OA Universe?
Because this question is asked so often, we have decided to devote
an entire section of the FAQ pages to answering it. Please note that
the arguments we present here are in keeping with a hard science
scenario based on a causal relativistic physical universe. We are not
criticizing other franchises for their choice to include such
phenomena. These FAQs are purely to answer the questions addressed to
the Orion’s Arm Universe and our stand on the matter.
Why do you allow
wormholes, and the exotic materials used to create them, but do not
allow FTL or even “hyperspace”?
The concept of wormholes, inflated from the quantum foam, and held open
with negative energy/exotic matter is one of the few feasible solutions
to FTL travel.
We have incorporated a version of the Alcubierre Warp drive within the
scenario, albeit an STL version, we call a void mote. These are
extremely difficult to produce and fairly limited in capability. None
of the works of Alcubierre, Van Den Broeck, Hillman, Natario or the
Loup et. al. proposal has demonstrated a solution to the causality
paradox inherent in FTL travel. This is because you cannot have FTL,
relativity, and causality in the same universe. A causal FTL universe
would require the assumption that Einstein was wrong and only Newtonian
physics apply. Because wormholes are not technically FTL travel they do
not conflict with causality.
A brief essay on causality:
I need the help of my friends from the Canadian Space Corps to help me
violate causality. I arrange for Alice to move out into space, and then
assume a position at rest relative to me. Bob has to fly past me at
event C, and Carol has to fly past Alice at event B. Things are
arranged so that Bob and Carol are moving with the same speed, and both
are moving in the direction from me towards Alice. At event A I use my
ansible to transmit a message instantaneously to Alice at event B.
Alice gives a copy of the message to Carol, who is flying past at the
time that Alice receives my transmission. Now, Carol and Bob are in a
different inertial frame to Alice and me, so they have a different
slice through spacetime that they consider the present. This means that
if Carol transmits the message to Bob with her ansible, then it will
arrive at event C, just as Bob's ship if flying past me. Bob can then
give me a copy of my message. The net result is that I have transmitted
a message into my own past. For any faster-than-light system there will
be some inertial frame in
which it appears to act instantaneously, and so the same argument may
easily be applied to any such system. Notice that you have to use the
ansible twice to make a causality
violation. You might think that things would be okay if your system
only worked once in the entire history of the universe, but this won't
work - in general there is no way in which to decide which use of the
system was the first. Another possible way to avoid causality
violations is to say that all the ansibles only work if they are at
rest relative to each other, so that they share the same
simultaneities. This, however, defines a preferred frame, so you'd have
to throw away the principle of relativity. Note that this violation of
causality does not involve a
closed timelike curve (parts of the message's trajectory are spacelike).
Hyperspace, otherwise known as large extra dimensions, exists in a
separate landscape at energy densities commensurate with the Big Bang.
At the current temperature of the universe, it has been compactified
down to a 3+1dimensional brane; the higher dimensional bulk is
fundamentally inaccessible except via gravitons.
As a final thought, although we have chosen to include wormholes, we
also understand they are purely theoretical, albeit on a pretty firm
basis with respect to General Relativity (a wormhole
“No-Go” theorem has yet to be proven; on the other hand,
ANEC violations are already found to exist in nature). It is a razors
edge, but the Orion’s Arm scenario is ultimately science fiction.
We have quite simply selected wormholes as the solution that, as far as
we know, does not violate modern understanding of the universe.
Why do you allow
wormholes, but not warp drive? Both are possible with exotic matter.
We do allow both. Wormholes do not violate causality, as they are an
artifact of non-simply connected manifolds in General Relativity. Warp
drives may violate causality; we allow warp metrics that do not possess
closed timelike curves (e.g., are non-FTL).
With warp drive
you never leave your own light cone, so why do you say that a warp
drive will create a paradox?
The warp drive metric creates a closed timelike curve the instant v
> c (with v being a property of the warp metric), which violates
causality. (If you prefer, causes a Cauchy horizon to form.)
Why can't you use
clarketech for FTL?
Even clarketech must ultimately obey the laws of physics. It may be
able to do things we find miraculous, but it cannot do things that are
logically or physically impossible.
Why not use
quantum entanglement to create an FTL communication system?
In order for information to be sent via quantum entangled qubits, a
classical bit of information describing the measurement basis must also
be sent, which adheres to v <= c.
Why not explain
FTL in terms of imaginary mass?
Because it has no basis in physics. All imaginary quantities found in
physics (e.g., quantum mechanical eigenstates) reduce to real
eigenvalues when measured. This property, called Hermiticity, is rooted
quite firmly in the mathematical basis of physics, and all possible
physical theories that describe the quantum behavior of the universe.
Related Pages:
Why is
there no time travel in OA?
Why
are certain things excluded?
