(fwd) Where Do We Go From Here?

incorrect. we can not know that without being their.

ALL we know is that LIGHT is not escaping.

based on that we ASSUME that the matter must be going faster than c.

this is a false assumption.

for all we know some as yet unknown property of the universe prevents the light from escaping.

in theory you would sit their just inside the ven horizon for eternity. can not escape and with infinite mass the black hole can not pull you further in since that would require infinite energy etc..

we are not even CERTAIN that black holes exist. we suspect with a high degree of possibility that they do or something like them.

we have yet to see/experience/measure etc.. a black hole directly.

Explain this. Please explain why FTL has ANYTHING to do with Time Travel.

if I travel to alpha centauri at 1c and 2c the only difference is that the first takes (roughly) 4 years and the second takes 2 years. positive time still to me.

I do not see how time travel occurs or causaulity is broken etc..

and even if time IS reversed or some such thing it matters not. only RELATIVE time (IE time for the objects moving in the referenced scenario) is affected.

and if time starts to go backwards so to speak that does NOT mean you would get younger. it could but that is not certain (till we try it)

Causaulity is not broken and time travel DOES NOT OCCUR

the speed with which relative time progresses for you make change but NO time traveling is occuring.

Chris Taylor

Mass fraction is how much of your rocket is propellant. If a 4 pound rocket has 1 pound of propellant, the mass fraction is 25%, for example. If the propellant performance is the same, the rocket with the highest mass fraction will gain the most velocity.

-dave w

Chris,

Your problem is, you think there's a universal "now." According to relativity, there isn't. Different observers of an FTL ship cannot agree on when something occurs.

The result is that you can screw up cause and effect.

The classic example is two spaceships going past each other at FTL, each with one missile. In the reference frame of the first ship, it can fire on the second ship and damage it. In the reference frame of the second ship, because of the FTL speeds, it will be hit by the missile before the other ship fires the missile. A quick thinking captain on the second ship can fire a missile at the first ship, destroying the missile before it's fired.

It's all about reference frames.

So how can the second ship have been shot if the missile on the first ship was blown up?

Any time machine can be turned into a faster-than-light rocket. Put a normal rocket capable of .999c into the time machine. Send it back 4.2 years. Launch the rocket four years ago. The rocket, from an observer on earth, takes one day to get to Alpha Centauri (if you time it right, at least). That works out to about 1500 times the speed of light or so. A massive cylinder, rotating at about half the speed of light, will make an excellent time machine for this purpose. That's the time machine from Frank Tipler's "Rotating Cylinders and the Possibility of Global Causality Violation." If you know tensor DiffEq., it's not a bad paper to read. If you don't, check out Larry Niven's story by the same title. (BTW: "Global Causality Violation" is the way you say "time travel" if you wanted someone to publish your physics paper back years ago.)

There's also a cute trick with wormholes, where you get one end moving at .999c. Your Deep Space Nine plot device becomes a cute little time machine.

Again, the book by Kip Thorne is a good read, although it sounds like a basic text on Special Relativity will help you and would be a first good read for you.

Being able to work the equations will give you a feeling for how it works.

Zooty

We know quite well why light does not escape a black hole. The escape velocity from a black hole is greater than the speed of light.

This in no way implies that anything inside a black hole moves faster than light. At the singularity in the center, our theories break down since there's no good theory of quantum gravity. But until that point, the equations say the matter is falling at near lightspeed.

Of course, as you point out, since it's inside the event horizon, it could be putting on a puppet show for all we know. If a black hole is, in fact, a new universe (as some theorists have suggested), then there may indeed be someone inside a black hole putting on a puppet show....

Even gravity inside the black hole cannot travel faster than the speed of light.

One of Stephen Hawking's grad students tried to explain this one to me in the early 1980s. Frankly, he threw up equations faster than I could believe, so I know that the math works, but don't ask me to explain it. I'm not sure there is a "physical" explanation other than "that's the way the math works out."

Heck, I doubt I can do that much tensor calculus and stuff any more, and I only had one semester of QM (or was that two? I forget). I'm not up for that level of math. That's worse than acting as a translator for two people, one who only speaks German, one who only speaks Portuguese. I've done it, but the headache afterward is devastating.

BTW: When Hawking first proposed evaporating black holes, everyone thought his Amyotrophic Lateral Sclerosis had finally gotten to his brain. They all forgot two things:

1. ALS doesn't affect the brain that way.
2. She who is Thermodynamics must be obeyed.

Hawking had the last laugh. And quite a few since.

Zooty

I love it when people say FTL travel isn't possible because it screws up causality... when in fact it doesn't, any more than a thunderstorm screws up causality. You know that there's been a lightning strike when you see the flash - you don't have to wait for the thunder to know that it happened. The same *may* be true for FTL travel - the ship can get to its' destination before the light of its' drive system, but that doesn't mean it travelled back in time.

It's more than just an optical illusion.

As I pointed out, you can set up situations where observers can't agree on what happens first. When it involves shooting missiles and watching them destroy the missiles before they're launched, it's more than an optical illusion.

Are you familiar with light cone diagrams? Look at where a time machine puts you on the diagram, and look at where FTL puts you on the diagram.

Right there, you should be able to see that one is equivalent to the other.

Zooty

It's very similar to "Don't Matter"...

David Erbas-White

Actually I understand the no universal now concept quite well that is why I have a problem with your statement.

THEIR IS NO "now" so their can be no "time travel" since time travel would require a now "reference" for you to be able to say I went forwards of backwards etc..

also please explain how cause an effect would be screwed up.

it amazes me how even nasa screws this one up. I see it so simply

you have "time" and you have relative time.

Here is the theory.

make a wormhole. or find one.

spin one end of the wormhole up to near C and hold it their for a period of time exceeding how long it would take you to get from the other entrance back to here.

theory being you would see yourself enter the wormhole.

this is utterly bogus and incorrect.

TIME IS NOT STOP.

time for the WORMHOLE entrance is slowed down.

so lets place some clocks.

1 in your ship and one at each worm hole opening.

lets say they all say 1200 hours.

now spin one up to C for 1 hours.

now all the clocks say 1300 except the spinning one it says 1200 still.

When you ENTER the wormhole you clock will say 1300 while INSIDE the wormhole your clock will say 1300 and when you EXIT it will say 1300

when you get back to the other hole 1 hour will have passed and your clock will say 1400 so will the exit clock. the entrance clock will still show

1200

but time is ONLY AFFECTED for the CLOCK and Wormhole entrance physically. NOT for your shipping passing into it.

even the nasa folks screw the pooch in THINKING that this dilation affects the rest of the universe. it does not. it only affect the specific matter that is moving near C

no time travel occurs. just the rate at which the passage of time appears to be progressing is affected.

in fact I do not even think ANY Time dilation is occuring at all. (this is my theory now)

I think time is completely unaffected. I think as matter speeds up motion SLOWS DOWN

this slow down also SLOWS DOWN clocks and their mechanisms

when you hit C mass is infinite and time is not frozen. MOTION is since it would require infinite energy to move an infinite mass.

just my theory. time after all is mearly motion when you really boil it down.

People also use this pathetic example to prove this casuality issue.

I lift off from earth. travel at 2c to a planet and then using a telescop watch myself lift off.

casuality is therfore broken. hagwash.

that is like saying if someone video tapes me leaving my house and then after getting to my destination I watch myself leaving my house on the video I am some how breaking casuality. Hogwash.

I firmly believe that time travel is utterly impossible. more than that I think the term time travel is a falsity. you can not travel in time. I also do not really see time as a dimension (will have to research this one more)

are inches a dimension ? no. inches are a means to MEASURE a dimension.

I see time the same way. simply a way to measure dimensions.

So when the astranauts go up is time slowing down or is just the matter slowing down resulting in the clock running slower ?

Please show me ONE example of how going faster than 670 million miles per hour can result in anything except me getting from a to b a little faster than if I was going 669 million miles per hour.

show me how time is affected in such a way as to cause "time travel" or casuality issues.

ALSO the term time travel is "nonsensical" unless you agree on a universal "now" to be in force.

that is NOT casuality.

that is PERCEPTION

if I shoot a video of you throwing a baseball.

I then show this video to 2 people at two different time is casuality broken ?

Off course not. who is right on when you threw the ball ? well me off course since I saw you do it live.

light is mearly polaroids of what happens.

just because the mail was late in getting you (your planet observers) your images that has NOTHING to do with casuality.

Chris,

The problem is, you see me blow up your spacecraft and so you blow up my spacecraft before I can blow up your spacecraft.

That is a definite causality violation. It's not just perception.

Zooty

In any reference frame, space-time can be divided into "space-like" and "time-like" zones.

Here's a web site that explains space-time diagrams:

Here's a web site that goes over the same problem in a different form, showing that FTL implies time travel:

If you want an explanation for the mouth of the wormhole, read the Kip Thorne book.

Part of the frustration you are experiencing is because we are not going through the actual math of these problems.

A course in special and general relativity would allow you to see your mis-interpretation of this theory. Unfortunately, there's no way I'm going to teach you that over the Internet.

Frankly, I don't have the time, and typing normal equations in ascii is just plain nasty. Typing tensor calc can be done, but I'd rather stick my finger in a light socket.

Zooty

DAMN, that was easy! I found on on "Star Trek, the Next Generation". What do I do next?

Uh, let's see - push the button labeled "extra spin cycle", right?

All your base are belong to us!!!

"Push the extra spin button 60 times"....

No, but some settling of contents may occur during handling.

THAT'S a wash cycle I've never heard of! Does it work on all hags, even the ones labeled "dry-clean only"?

Ahem - from the viewpoint of the outside observer, matter does not enter the black hole but merely hovers forever at the event horizon. This may be interpreted to mean that an infinite amount of energy IS needed to get it across the horizon, since it is being subject to a very large force forever, without actually making it across.

You showed me NO casuality violation.

your example was non sensical. explain it in more detail.

If I see you blow up my spacecraft then I am not longer "here" to blow up yours. (if its my spacecraft then well duh I am in it :-)

also anything SEEN from outside the perspective has already happened. IE its in the past.

NO casuality is broken.

Casuality deals with Cause and Effect. NOT percieved Cause an effect. that is not relevant.

Only what ACTUALLY occured before and after.

BB,

Thanks for the laugh! After a day of physical therapy and Doctors, I needed that.

Thanks again,

Patrick - physics ex-junkie, now look>"Chris Taylor Jr" wrote:

I do next?

Hey, no problem! I'm booked here 'til Friday, when it's on to Vegas. Try the fish!

Chris,

Go take a college class on Special Relativity. I'd have to teach you at least the first half of the semester so that you could work through the math.

If you ask the professor, I'm sure he'd be glad to work through the problem for you.

Then you can come back and tell me that, while I did a crappy job of explaining it, I was right.

Zooty

alas I do not think you are.

in order for causality to be broken time travel MUST occur.

you have not show me how going faster has anything to do with TIME TRAVEL and not just relative time but time for everyone else since that is the time that matters when causality is an issue.

I actually have a pretty good mental understanding of this kind of stuff. not the math but the mental aspect of it IE understanding it.

the math is simply our way of trying to put reason to what is seen. I do not need to know how much mass two objects have in order to say which is heavier.