On 21 Jul 2010 at 23:00, wrote:
> HOLD THE PHONE!!! Your mass doesn't change *from your own
> perspective*!!! So the effects of relativity *do not affect you*,
> only how other's see you?
They aren't really "effects" in the sense that you are thinking.
Relativity is about the geometry of space-time.
A more "everyday" example:
Imagine you have several points marked on a sheet of paper. And you
and a friend both have ytransparent sheets of plastic marked with an
X-Y grid.
The paper is on a circular table. Each of you is asked to lay your
grid on the table with the X axis being left to right and the y axis
going away from you. Then you are to plot X-Y co-ordinates of each
point.
You both get *different* co-ordinates unless you sit at the same
spot.
But if you are asked to calculate the distances between the points
from your co-ordinate lists, you'll get the same distances:
d = sqrt((x1-x2)^2 + (y1-y2)^2)
Your corodinate axes were rotated with respect to each other (sand
had different origin point) which is why the co-ords for each of you
came out differently.
You can at a Z axis and the formula is
d = sqrt((x1-x2)^2 + (y1-y2)^2 + (z1-z2)^2)
Okay, fine.
When you add time, things get wonky. Instead of "distance" you are
measuring a quantity called "interval". And due to time being
"special" (or rather the way time is joing to space being a bit odd)
the formula gets weird.
s = sqrt((x1-x2)^2 + (y1-y2)^2 + (z1-z2)- (c*t1-c*t2)^2)
While observers may disagree as to the space and toime co-ordinates
of events, they will always agree on the interval between any pair of
events.
> So, really, *you* can go faster then light, you just can't be
> observed doing it? No, wait. In order to think of yourself moving at
> that speed you need to accelerate the universe around you to that
> speed, and if that universe is suffering from the same affect that it
> thinks you are suffering from...aaaarrrrggghh.
See https://secure.wikimedia.org/wikipedia/en/wiki/Special_relativity
It answrs all your questions and more.
But basically you can have any *two* of these three:
1. Relativity (special relativity is *very* well tested, any
replacement would have to predict the exact same measurements for all
the observations and experiments we have)
2. FTL
3. causality (ie effects must have causes)
If you go for *strict* causality (effects must preceed causes
according to all observers) you *cannot* have FTL without throwing
out relativity.
Also, remember that formula for interval?
If you work it out for observers at different velocities, youll find
that *any* situation where you have event A (ship at starting point)
and event B (ship at destination) such that in some frame the ship
arrived faster than light could cross the distance, there will ve a
set of velocities such that those observers saw the ship arroive
before it left.
FTL is *always* time travel in at least one frame of reference.
Doesn't matter if you go thru another universe, because wat matters
are the spacetime coordinates of your departure and arribal, not
"how" you got between them.
It's possible to have FTL and preserve *global* causality, but not
"local" causality.
So in such a universe some events will be seen by some observers to
have effects that occur before the cause.
Such a universe could have causal loops (ie I did X because someone
from the future came back and told me to, but he did that because
what I did required that he come back)
But it can't have paradoxes. In fact, there are a number of papers
working from quantum physics to show that in such a universe you
*can't* change the past. Trying would result in "random" quantum
events changing probability to *force* the outcome.
Om the other hand, much like the bit where quantum states don't
"collapse" until observed, you'd be free to do what you wanted on a
trip to the past as long as you had no idea what was "supposed" to
happen (it's rather more complex than that, but that gets across the
general idea).
For example, if you *can* shoot that guy, he wasn't your grandfather.
:-)
Oh yeah, if you buld a time machine (or a time communicator) you
can't go back before the moment it was turned on for the first time.
:-)
sopme folks over on the TML worked out what it'd take to go back in
time (or send messages to the past) using Traveller tech. Doable, but
a bit of a pain. And not very useful.
> So then, I would guess that the rest of the universe would seem more
> massier? Hmmmmmm.
>
> Hang on, if your twin sees you as moving at .9c and you are seeing
> him move at .9c, why does anyone age differently?
Assume we can boost the one twin to .9 c instantly, so we don't have
to worry about how he ages *during* the acceleration.
So, at this point *each* twin sees the other aging more slowly.
So we accelerate the twin again and bring him back.
He's aged more slowly. But that's becauuse he's been accelerated
*twice* and the other hasn't. Non-symmetrical situation. If we don't
bring them together, which one is aging slower is a nonsense question
(it depends on who is observing and from where).
--
Leonard Erickson (aka shadow)
shadow at shadowgard dot com