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Author Topic:   The Twins Paradox and the speed of light
MasFina
Junior Member (Idle past 5146 days)
Posts: 1
From: East Coast
Joined: 10-07-2008


Message 76 of 230 (485322)
10-07-2008 11:00 AM
Reply to: Message 71 by cavediver
10-06-2008 1:43 PM


Re: Here is the simple explanation....maybe
After lurking for too long I wanted to thank all the participents in this thread for convincing me to sign up. This discussion has been informative and useful. Thanks again.
And just to make sure I'm on topic: Good point!

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cavediver
Member (Idle past 3644 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 77 of 230 (485324)
10-07-2008 11:04 AM
Reply to: Message 76 by MasFina
10-07-2008 11:00 AM


Re: Here is the simple explanation....maybe
Cool Welcome aboard!

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boysherpa
Junior Member (Idle past 5372 days)
Posts: 19
From: Lomita, CA
Joined: 10-04-2008


Message 78 of 230 (485805)
10-11-2008 8:06 PM
Reply to: Message 65 by New Cat's Eye
10-05-2008 12:45 PM


Re: why is this a paradox?
Thanks for the reply,
Read that post, nothing of the sort there. You may be confusing algebra with explanation.
I have quite a firm grip on these calculations. I am, actually, quite familiar with most things scientific. That is not my point. Let me list my observations, so that some of you could help.
1. Consider 3-space (x,y,z). A change in 3-space has two characteristics we will agree upon. The first is innocuous - a function f(x,y,z) describing a change in coordinates in 3-space is continuous. In other words, no magic teleportation. Second, and this is important, the function f(x,y,z), describing change in coordinates, instantiates time or necessitates the creation of time.
2. Examples of allowed changes in 3-space include: motion resulting in change in coordinate in a positive or negative direction relative starting point, a return to any previous coordinate desired, a wide range of velocities and accelarations decribing changes in coordinates.
4 (no, 3 sir). Consider the dimension of time. A change in this dimension is in no way similar to a change in 3-space. There is no instantiation of time with a change of time, if you follow my meaning. One may not move arbitrarily amongst time coordinates. There is no concept of time velocity or acceleration. In fact, there seems to be only one time coordinate, that being "present".
4. Finally, time has only one direction, an effect which we call causality, and this is firmly rooted in the space-time diagrams folks have interspersed among the posts in this thread. (It is therefore an inherent assumption in the calculations as well.) There is no corresponding restriction in 3-space.
So, I am confused about how time is considered on equal footing with 3-space. I fully understand the equations. Heck, I work with such mathematics more than most of you do. But I understand that models do not equal reality, and often do not explain reality.
It could be that if we accept all these caveats, that we may model space-time as including a psuedo-dimension called time. In this case, time as a dimension would merely be a convenient mathematical model. Is that what SR is saying?

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cavediver
Member (Idle past 3644 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 79 of 230 (485833)
10-12-2008 5:43 AM
Reply to: Message 78 by boysherpa
10-11-2008 8:06 PM


Re: why is this a paradox?
I fully understand the equations. Heck, I work with such mathematics more than most of you do.
Really? What do you do? It's always great to find direct applications of complex equations in the workplace, rather than just in academia. I used to work in derivatives - actually, I do feeel a bit guilty at the moment, as one of my main areas of expertise is calculating a bank's exposure to complex credit backed securities... Perhaps if I hadn't left the sector all those years ago
Consider 3-space (x,y,z)
Ok, is this simple Euclidean space, with the basic Pythagorean metric?
a function f(x,y,z) describing a change in coordinates in 3-space is continuous.
I'm unsure as to how f() represents a change in coordinates - is f a vector, a more general tensor, or is it just a scalar as you have written? Let's say we go from the triple (x,y,z) to (x+dx, y+dy, z+dz) - how do we encode this change in f? And I'm not sure what you mean by f(x,y,z) necessiating time - do you mean we should really write f(x,y,z,t)?

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mogplayer101
Junior Member (Idle past 5420 days)
Posts: 4
From: Canada
Joined: 05-25-2009


Message 80 of 230 (509898)
05-26-2009 12:05 AM
Reply to: Message 45 by Jester4kicks
07-03-2008 1:37 PM


Ok, here is the straight goods of an easy to understand explanation of how time dilation due to velocity works. Ok, now picture if you would (as in this picture) a spaceship that has two mirrors on either side of the cargo bay, and for arguments sake the mirrors are one meter apart, so the photon of light has to move two meters to get there and back. Now if the shuttle is traveling at half the speed of light, the shuttle will move one meter sideways as the photon is moving between mirrors, now the light is no longer traveling in a straight line to an observer off of the ship, but in a triangular shaped line, therefore the photon is now traveling a longer distance, and will take a longer time outside of the ship to complete its journey. Check out this page.
http://musr.physics.ubc.ca/~jess/p200/str/str9.html
-Help at all?

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Kev The Thiest Evolutioni
Junior Member (Idle past 5410 days)
Posts: 4
From: Ipswich, Suffolk, England
Joined: 06-05-2009


Message 81 of 230 (511095)
06-06-2009 4:53 AM


I presume tthe reason is that velocity equals distance devided by time. Therefore time equals velocity times distance.

Replies to this message:
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Percy
Member
Posts: 22393
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.2


Message 82 of 230 (511112)
06-06-2009 8:10 AM
Reply to: Message 81 by Kev The Thiest Evolutioni
06-06-2009 4:53 AM


Hi Key,
Below each message are a row of buttons. One of those buttons is labeled "Reply" and is for replying to that specific message. When replying to a specific message it is better to use that button, because then links to and from the messages are also created.
About this:
I presume tthe reason is that velocity equals distance devided by time. Therefore time equals velocity times distance.
That's an interesting universe you live in, but here in the real world we find that t=d/v.
--Percy

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lyx2no
Member (Idle past 4717 days)
Posts: 1277
From: A vast, undifferentiated plane.
Joined: 02-28-2008


Message 83 of 230 (511120)
06-06-2009 8:45 AM
Reply to: Message 81 by Kev The Thiest Evolutioni
06-06-2009 4:53 AM


An Acre Per Hour
velocity times distance.
The E=mc2 of lawn mowing theory.

Ridicule is the only weapon which can be used against unintelligible propositions. Ideas must be distinct before reason can act upon them.
Thomas Jefferson

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WaveDancer
Member (Idle past 5405 days)
Posts: 37
From: NSW Australia
Joined: 09-14-2008


Message 84 of 230 (511542)
06-10-2009 9:07 AM


A twist
"Scientists have found that, when twins are orbiting a massive object, time dilation can cause the accelerated twin to be older if that twin is moving slower than the other twin; in this case, velocity is the deciding factor of age, and the twin with the greater velocity is younger."
http://www.physorg.com/news163738003.html
I guess this just goes to prove how difficult facts in cosmology are to pin down and how ambiguous the whole concept is.

Replies to this message:
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onifre
Member (Idle past 2951 days)
Posts: 4854
From: Dark Side of the Moon
Joined: 02-20-2008


Message 85 of 230 (511635)
06-10-2009 6:22 PM
Reply to: Message 84 by WaveDancer
06-10-2009 9:07 AM


Re: A twist
I guess this just goes to prove how difficult facts in cosmology are to pin down and how ambiguous the whole concept is.
There is one minor problem with this statement, the "twin paradox" wasn't actually a fact.
Source
quote:
While there are a variety of possible examples of the Twin Paradox in action, let's consider the following version. Prime and Unprime are twins; they say their farewells as Prime boards a train. Prime takes a trip on the train to a distant station (distance L), at uniform velocity v (a considerable fraction of the speed of light). Upon reaching the distant station, Prime takes a return train at the same speed, returning to meet Unprime at the original station. Unprime has been waiting patiently at the original station for the return of Prime. Upon arriving at the original station, Prime and Unprime discover that Unprime has aged considerably, yet Prime hasn't aged much at all.
The "paradox": Special relativity says that physics is the same in reference frames that move at a uniform velocity relative to one another. Observers in any two frames moving relative to one another should not be able to make any observation that indicates which one is "actually" in motion. So, how is it that one of the twins (Prime) is younger than the other? Does this mean one of the twins was "actually" in motion while the other was not?
Like all such paradoxes the paradox is only apparent. In this case, Prime has actually taken a trip. That is, Prime has left the Frame of Reference of Unprime (feeling an initial acceleration at the beginning of the trip), then, after some time, Prime again feels an acceleration as Prime slows to a halt and turns around (boards the return train), again accelerating up to speed, then finally halting back at the original station. Prime has felt lots of accelerations; Unprime has felt no accelerations. Therefore, Prime did actually do something "out of the ordinary" --- it might not be unreasonable to find that Prime and Unprime have had different experiences. Indeed, it appears that Prime has experienced less time duration during the separation of the twins than Unprime has experienced.
The key point is "acceleration". Further in the link you'll find the Twin Paradox without acceleration as well.
- Oni

Petition to Bailout Comedy The Laugh Factory is imploring Congress to immediately fund what owner Jamie Masada calls an "Economic Cheer-Up." If Congress fails to act quickly, the Laugh Factory comedians are planning to march to Washington and plea to President Obama.

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WaveDancer
Member (Idle past 5405 days)
Posts: 37
From: NSW Australia
Joined: 09-14-2008


Message 86 of 230 (511682)
06-11-2009 6:49 AM
Reply to: Message 85 by onifre
06-10-2009 6:22 PM


Re: A twist
Hmmmm I always thought it was a fact. One twin gets on a spaceship which goes at the speed of light the other one stays home. When the spaceship returns the twin that stayed at home is older. FACT! At least I thought it was. Owell I still have alot to learn then.

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Percy
Member
Posts: 22393
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.2


Message 87 of 230 (511691)
06-11-2009 8:55 AM
Reply to: Message 86 by WaveDancer
06-11-2009 6:49 AM


Re: A twist
I'm not sure what Onifre is getting at, but the twin paradox is a fact. It not only has a very strong theoretical foundation, it's been verified experimentally with atomic clocks sent up in airplanes and into space.
--Percy

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cavediver
Member (Idle past 3644 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 88 of 230 (511716)
06-11-2009 11:38 AM
Reply to: Message 87 by Percy
06-11-2009 8:55 AM


Re: A twist
but the twin paradox is a fact.
Perhaps the confusion is that there is no paradox. The effect is real but there is nothing paradoxial about it...

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onifre
Member (Idle past 2951 days)
Posts: 4854
From: Dark Side of the Moon
Joined: 02-20-2008


Message 89 of 230 (511720)
06-11-2009 12:21 PM
Reply to: Message 88 by cavediver
06-11-2009 11:38 AM


Re: A twist
Perhaps the confusion is that there is no paradox. The effect is real but there is nothing paradoxial about it...
Thanks, cavediver. That's what I meant.
I guess I should have expressed that better.
- Oni

Petition to Bailout Comedy The Laugh Factory is imploring Congress to immediately fund what owner Jamie Masada calls an "Economic Cheer-Up." If Congress fails to act quickly, the Laugh Factory comedians are planning to march to Washington and plea to President Obama.

This message is a reply to:
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Trae
Member (Idle past 4307 days)
Posts: 442
From: Fremont, CA, USA
Joined: 06-18-2004


Message 90 of 230 (534153)
11-05-2009 11:28 AM
Reply to: Message 88 by cavediver
06-11-2009 11:38 AM


Twin Paradox Revisited Sans Rocket-ships.
Twin Paradox Revisited Sans Rocket-ships.
SciFi's Assumption: Mystical magical aliens have some sort of FTL or FTL-like travel. Specifically some means from getting from interstellar point A to B 'instantaneously'. In SciFi this 'solves the problem' for SciFi authors and audiences, but would it actually work?
Acceleration isn't limited to spaceships and visitation takes time, so wouldn't the twins paradox still be in play since those objects (earth and the alien home-world) are under the influence of different bodies in different gravitational fields?
While I presume this comes into play within our own galaxy, I think it might be easier to use an example of aliens from a different galaxies. If aliens from galaxy A (a galaxy not in our local group) somehow managed to arrive on Earth instantaneously, and if galaxy A and galaxy B are hurdling away from each other, it seems to me that time would pass at a different rate on the alien planet than on Earth.

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