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Author Topic: Causality
Jonathan Singh
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Icon 1 posted September 20, 2003 15:51      Profile for Jonathan Singh     Send New Private Message       Edit/Delete Post 
Ok, Faster than light travel is possible, plenty of things go faster than it, even in vaccuum...

so then, wouldn't that violate causality? EPR paradox: The particle will get there before it gets there... sort of, so the reaction comes before the action

does that make the reaction the action and vice versa? or does it just not work?

and what about time travel? If i go back into time and kill my grandfather before my father is born, what happens? I can't kill my grandpa if i'm not born, and if i kill him, i'm not born.

and when particles that we know of travel faster than the speed of light, they appear to get there before they have even left.

it's weird, so does this mean that anything on a day to day basis will change? or just that our universe just gets bigger and bigger and more and more enigmatic with everything we know.

the more we know, the more we know we don't know?

so then, another theory is that since the particles are able to get there before they leave, that at a sub-atomic level, every single point is the same, meaning that, well, everywhere is here.

It's like that episode of voyager where they attain warp 10, speed = infinity, they are everywhere all at once.

what do you guys think?

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The Famous Druid

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Icon 1 posted September 20, 2003 16:30      Profile for The Famous Druid     Send New Private Message       Edit/Delete Post 
quote:
Originally posted by Jonathan Singh:
so then, wouldn't that violate causality?

No, it wouldn't violate causality, any more than seeing the baseball bat hit the ball before you hear the 'crack' does.

We have this notion of causality because Einstein told us that nothing can travel faster than light, so the causal link between 2 events is limited to c.

If we later find out that, for example, tachyons can travel at speeds greater than c, then that would be the new speed limit of causality, and we'd get used to the idea that some causes can produce an effect before we've seen the cause.

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If you watch 'The History Of NASA' backwards, it's about a space agency that has no manned spaceflight capability, then does low-orbit flights, then lands on the Moon.

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Lex
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Icon 1 posted September 20, 2003 19:34      Profile for Lex   Author's Homepage     Send New Private Message       Edit/Delete Post 
The only particles I've heard of that can exceed light speed are the massless ones, notably light itself.

As for the grandfather paradox, it depends on your model. The usual model goes something like this: Your very existence proves that, whatever you do in the past, you will fail to be able to do anything that changes the future. Because it has already happened. You were already there. Perhaps your grandpa had an odd experience when he was young in which he was assaulted by a strangely dressed and very persistent man, whom he finally killed out of self defense.

Another model involves one-way parallel time streams. You can't go into your own past, but you can go into parallel pasts. In which case killing your grandfather is meaningless because he isn't really your grandfather.

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Icon 6 posted September 20, 2003 20:21      Profile for unclefungus   Author's Homepage     Send New Private Message       Edit/Delete Post 
I find it best to not think about things like that. But if you want to boggle the mind, I try to figure out real world things may accually make a difference like:

Why do we park on a driveway and drive on the parkway?
why are apartments together?
If corn oil is made from sqeezing corn, what is baby oil made from?

OK, I'll stop. [Big Grin]

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The Famous Druid

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Icon 1 posted September 21, 2003 00:39      Profile for The Famous Druid     Send New Private Message       Edit/Delete Post 
quote:
Originally posted by Lex:
As for the grandfather paradox, it depends on your model. The usual model goes something like this: Your very existence proves that, whatever you do in the past, you will fail to be able to do anything that changes the future. Because it has already happened. You were already there. Perhaps your grandpa had an odd experience when he was young in which he was assaulted by a strangely dressed and very persistent man, whom he finally killed out of self defense.

Another model involves one-way parallel time streams. You can't go into your own past, but you can go into parallel pasts. In which case killing your grandfather is meaningless because he isn't really your grandfather.

A few variations I've read of in Science Fiction.

1. Parallel Universes. If you travel back in time and change something, you create a new 'fork'. Your own time stream remains, but now there's another where your granddad was murdered.

2. The "time protects itself" model, from "The Doomsday Book" (not entirely sure of the title). Basically, if you armed yourself and went into your time-machine with the intent of murdering your granddad, the machine would simply refuse to let you travel, or would deposit you at a time after your granddad had already died of natural causes. Only by making the most rigourous precautions to prevent such damage could you time travel at all. Many attempted time trips failed for no readily apparent reason, but presumably because had they gome ahead, some such event would have happened by accident, so the trip never happened. Don't think about this too carefully, you'll get a headache.

3. The "You Can't Change Anything" model. You can go back in time and observe, but not interact. No one can see you, you can't move objects, etc. Set off a bomb in the delivery room where Hitler is being born, no-one in the room will notice.

4. The "You Can't Change Anything" model (mark II). You can go back and blow up Hitler, but when you return to your own time, nothing has changed, Hitler still did his thing, WW2 still happened, there's no record of your assasination ever happening.

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If you watch 'The History Of NASA' backwards, it's about a space agency that has no manned spaceflight capability, then does low-orbit flights, then lands on the Moon.

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Jonathan Singh
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Icon 1 posted September 21, 2003 08:39      Profile for Jonathan Singh     Send New Private Message       Edit/Delete Post 
So then, if we use Minority Report for an example, what if we see the future, then stop the reaction before the action?

I.E. Stopping the murder before the murder.

The murder is the action, and the aprehending of the murderer is the reaction.

but the reaction comes before hand.

but those two are corelated, not causality related... damn

so then what about the EPR paradox, with the two particles? And every single point being the same at a sub-atomic level?

P.S. Go to the reviews section and reply to the half-life/BF1942 thread!!!

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Xanthine

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Icon 1 posted September 21, 2003 16:43      Profile for Xanthine     Send New Private Message       Edit/Delete Post 
quote:
Originally posted by Jonathan Singh:
Ok, Faster than light travel is possible, plenty of things go faster than it, even in vaccuum...

Pardon my ignorance, but what's faster than c?

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Jonathan Singh
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Icon 1 posted September 21, 2003 19:02      Profile for Jonathan Singh     Send New Private Message       Edit/Delete Post 
plenty of things, a university (either Berkley or MIT) managed to accelerate a particle at to roughly 2C. What they observed (and all the computer data they collected) was that the particle arrived there before it left. It knew what was going to happen.

and the EPR paradox, where 2 particles are emited from a source at the same time. They should always have oposite spin, i think. When the distance between the two becomes very great, if you change the rotation of one particle, the other one changes instantly, which means that something is telling the other particle to change at faster than light speeds.

i'm not sure if that's the EPR paradox, somebody correct me.

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The Famous Druid

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Icon 1 posted September 21, 2003 19:27      Profile for The Famous Druid     Send New Private Message       Edit/Delete Post 
quote:
Originally posted by Xanthine:
quote:
Originally posted by Jonathan Singh:
Ok, Faster than light travel is possible, plenty of things go faster than it, even in vaccuum...

Pardon my ignorance, but what's faster than c?
C++ ?
[Big Grin]

--------------------
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dragonman97

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Icon 1 posted September 21, 2003 20:13      Profile for dragonman97   Author's Homepage     Send New Private Message       Edit/Delete Post 
quote:
Originally posted by The Famous Druid:
quote:
Originally posted by Xanthine:
quote:
Originally posted by Jonathan Singh:
Ok, Faster than light travel is possible, plenty of things go faster than it, even in vaccuum...

Pardon my ignorance, but what's faster than c?
C++ ?
[Big Grin]

Nah, much more bloated...linking of objects at startup would make that nearly impossible.

Perl, OTOH...nah, not really :-P.

Besides, she said 'c.' Unless it's VB we're talking about, 'c' != "C" [Big Grin] .

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The Famous Druid

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Icon 1 posted September 21, 2003 20:47      Profile for The Famous Druid     Send New Private Message       Edit/Delete Post 
quote:
Originally posted by dragonman97:
quote:
Originally posted by The Famous Druid:
quote:
Originally posted by Xanthine:
quote:
Originally posted by Jonathan Singh:
Ok, Faster than light travel is possible, plenty of things go faster than it, even in vaccuum...

Pardon my ignorance, but what's faster than c?
C++ ?
[Big Grin]

Nah, much more bloated...linking of objects at startup would make that nearly impossible.

Actually, there are some tricks with templates that can cause fairly substantial bits of code to be evaluated at compile time.

You can't beat no time at all for speed.

Unless you start producing the result _before_ the program is written, but that would violate causality.....

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spungo
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Icon 1 posted September 22, 2003 02:37      Profile for spungo     Send New Private Message       Edit/Delete Post 
quote:
Originally posted by Jonathan Singh:
plenty of things, a university (either Berkley or MIT) managed to accelerate a particle at to roughly 2C.

Bullsh*t. Any particle with any mass at all would require infinite energy to get to c and, in doing so, would acquire infinite mass.

How 'bout a link, pal?

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littlefish
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Icon 1 posted September 22, 2003 03:35      Profile for littlefish   Author's Homepage     Send New Private Message       Edit/Delete Post 
I thought that certain (hypothetical) particles (tachyons?) were allowed to travel faster than light, as long as they never travelled slower (or something like that). It doesn't take infinite energy to travel faster than c, it just takes infinite energy to accelerate something to c. Thus if you create a particle that is travelling faster than light when it is created, then it is all good.

Also, there are particles with no mass at rest.

But I haven't done any physics for 7 years (unless you count physical chemistry), and am probably mostly wrong.

So remember kids, don't try to replicate this at home. Stop trying to manufacture photons and tachyons! A little knowledge is a dangerous thing!

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littlefish
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Icon 1 posted September 22, 2003 03:44      Profile for littlefish   Author's Homepage     Send New Private Message       Edit/Delete Post 
Well, a quick google found me here
It seems that quantum tunneling allows you to observe things moving faster than light, but it doesn't violate causality. Or something.

As Bohr once said, "If you are not shocked by quantum theory, then you have not understood it"

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The Famous Druid

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Icon 1 posted September 22, 2003 05:01      Profile for The Famous Druid     Send New Private Message       Edit/Delete Post 
quote:
Originally posted by littlefish:


As Bohr once said, "If you are not shocked by quantum theory, then you have not understood it"

LOL !

I remember my physics lecturer at the end of the Quantum Physics part of the course, asking
"Who's understood what we've covered in this unit?"
About 1/10 of the class raised their hands (I wasn't one of them)
He pointed accusingly at one and said
"Well, you just haven't been paying attention! "

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If you watch 'The History Of NASA' backwards, it's about a space agency that has no manned spaceflight capability, then does low-orbit flights, then lands on the Moon.

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Icon 3 posted September 22, 2003 16:02      Profile for MacManKrisK     Send New Private Message       Edit/Delete Post 
quote:
Originally posted by littlefish:
I thought that certain (hypothetical) particles (tachyons?) were allowed to travel faster than light, as long as they never travelled slower (or something like that).

Ah! Finally, the last episode of Star Trek : The Next Generation makes sense to me!

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get rich and you still die"


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Xanthine

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Icon 1 posted September 22, 2003 16:10      Profile for Xanthine     Send New Private Message       Edit/Delete Post 
quote:
Originally posted by Jonathan Singh:
plenty of things, a university (either Berkley or MIT) managed to accelerate a particle at to roughly 2C. What they observed (and all the computer data they collected) was that the particle arrived there before it left. It knew what was going to happen.

Um, if they'd done that I woulda heard about it. Even though I can't do quantum physics to save my life, I would have a hard time missing the cover story in Nature or Science which is where that story would show up. I never took a quantum physics course, but I definitely learned that nothing in reality goes faster than c. If someone manages to do that, and REPRODUCE it, then, to paraphrase my prof, they've got a trip to Stockholm in their future

littlefish, that just blew my mind. [Eek!]

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Jonathan Singh
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Icon 1 posted September 22, 2003 18:23      Profile for Jonathan Singh     Send New Private Message       Edit/Delete Post 
quote:
Originally posted by Xanthine:
quote:
Originally posted by Jonathan Singh:
plenty of things, a university (either Berkley or MIT) managed to accelerate a particle at to roughly 2C. What they observed (and all the computer data they collected) was that the particle arrived there before it left. It knew what was going to happen.

Um, if they'd done that I woulda heard about it. Even though I can't do quantum physics to save my life, I would have a hard time missing the cover story in Nature or Science which is where that story would show up. I never took a quantum physics course, but I definitely learned that nothing in reality goes faster than c. If someone manages to do that, and REPRODUCE it, then, to paraphrase my prof, they've got a trip to Stockholm in their future

littlefish, that just blew my mind. [Eek!]

Here's a link, but I couldn't find the actually University. This page refers to it as the Wang et al. experiment, and is briefly described.

P.S. I find it kinda sad that somebody actually disqualified information based on the fact that "I would have heard about it, but i didn't". Seems kinda... well, chinsy, border line lame. You must be able to find some other reason to disqualify it! Like it coming from a kid, or from an anonymous internet source, or SOMETHING, ANYTHING that makes more sense than that. That's like saying the sun didn't come up this morning because i didn't see it come up.

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Jonathan Singh
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Icon 1 posted September 22, 2003 18:24      Profile for Jonathan Singh     Send New Private Message       Edit/Delete Post 
if nothing goes faster than C, explain the EPR paradox to me, then. Please.

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Jonathan Singh
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Icon 1 posted September 22, 2003 18:56      Profile for Jonathan Singh     Send New Private Message       Edit/Delete Post 
quote:
Originally posted by The Famous Druid:
quote:
Originally posted by Xanthine:
quote:
Originally posted by Jonathan Singh:
Ok, Faster than light travel is possible, plenty of things go faster than it, even in vaccuum...

Pardon my ignorance, but what's faster than c?
C++ ?
[Big Grin]

To quote a famous programmer:

"C made it easier to shoot yourself in the foot. C++ made it harder, but you succeded in blowing your entire leg off".

Faster? You decide.

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Jonathan Singh
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Icon 1 posted September 22, 2003 20:13      Profile for Jonathan Singh     Send New Private Message       Edit/Delete Post 
For all you freaking non-believers out there who say it didn't happen cuz you didn't hear about it.

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dragonman97

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Icon 1 posted September 22, 2003 21:05      Profile for dragonman97   Author's Homepage     Send New Private Message       Edit/Delete Post 
quote:
Originally posted by Jonathan Singh:
For all you freaking non-believers out there who say it didn't happen cuz you didn't hear about it.

Hey there...be a bit nicer about it, okay? You only linked to the page that was cited off cheezi's page - you didn't actually point to the part you are talking about - care to show us some specifics? From what I can see, they did not get *matter* to move faster than c.

A second point I'd like to ask (or someone else would, even): Is it reproducible?

/me is too tired to read up more about this stuff, and crawls into bed...moving far slower than c.

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Jonathan Singh
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Icon 1 posted September 22, 2003 21:15      Profile for Jonathan Singh     Send New Private Message       Edit/Delete Post 
Yeah, you're right. I'm sorry Xanthine. I've just been really ribbed recently, having to repeat final year of High School in the IB with a new grade that's a bunch of (for the most part) pricks. They've been on my case everytime i point something out that they didn't know. I just got kinda upset cuz it seemed like EVERYBODY was doing it.

Yes, it's reproducible, as for matter itself, i'll get back to you on that, but one would assume that matter entering a black hole would at some point reach C, and be accelerated to it. non? or did i just pull that outta my ass?

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Jonathan Singh
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Icon 1 posted September 22, 2003 21:18      Profile for Jonathan Singh     Send New Private Message       Edit/Delete Post 
P.S. isn't energy and matter one in the same? I'm probabbly way off on that

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dragonman97

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Icon 1 posted September 22, 2003 21:27      Profile for dragonman97   Author's Homepage     Send New Private Message       Edit/Delete Post 
I'm relatively [^_~] certain that they are *not* the same thing [Smile] . *

Re: the black hole thing - I think you are probably pulling that out of your ass. littlefish used one of my favorite quotes: "A little knowledge is a dangerous thing!"

*And remember kids, Star Trek physics teach us that matter & energy are different, and this is why things in the holodeck, made of energy, cannot exist in the real world. In the confines of the holodeck, energy is seemingly transformed into matter. Special, but different, matter/energy combinations/transformations are used to make things through the replicator system. And the transporters use a very special matter::energy conversion system, with Heisenberg compensators to transfer matter through space.

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