The problem is a paradox, or a seeming paradox. How can a twin possibly be older then her twin brother?
Moreover, why is it the guy the one who ages faster? After all, it's relativity, is it not?
Relativity says there is no difference in the points of view of either twin, since Chere can always say that is her brother who is moving very fast away from her.
So who is right?
It was just this kind of thing that led Einstein to realise that having Inertial Frames was not enough. An Inertial Frame is a point of view that conforms to all laws of physics in a consistent manner. Einstein said that all these are equivalent.
It is like saying that you cannot detect absolute motion
This is true, except when there are accelerations or gravity are present (they are equivalent). This so hard, it took Einstein 11 years to formulate it. He called it General Relativity.
This is how we resolve the paradox. If we realise that for Special Relativity, accelerations are not invloved, so the twins Inertial Frame (points of view) are NOT equivalent
Why? Because in order to return, Chere has to slow down, stop, turn around and speed up again.
That means we can actually TELL who is moving, and it is Chere, so she stays younger.
More details can be found here....
http://math.ucr.edu/home/baez/physics/Relativity/SR/TwinParadox/twin_gr.html#sr_vs_gr
Friday, January 04, 2008
Travelling Families - Solution
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8 comments:
Forward time travel is so simple a child can understand it (SR - I was 14 when I first understood this).
Backward time travel is so far in the future (manipulating black holes via GR) that it is to all intents and purposes impossible, plus there is the limitation that you could only travel back to the time you invented the "machine" and no further (GR again)
This may be one reason why Stephen Hawking has said " If backward time-travel were possible, why have we not been invadwed by tourists from the future?"
A striking example of the time travel backwards paradox is given by the "invention" of Transparent Aluminum in ST4. Where did the information originate?
Allow me to posit that we already have a form of time travel backwards in time and are quite aware of it. Everytime we or some astronomer looks at the heavens, this is looking into the past. What has been missing to date is our ability to be at any point along that past in a physical sense. Yet, we are constantly moving into the future. There seems to me no present. This strikes me as paradoxical to the mind.
I add in the posed Twin Paradox, we may tend to think of this event as a straight line event, whereas since time does change for both, the spacecraft would follow a curved-space path in order to arrive at the (?future?) location of Earth. Or so it seems to me.
Is it possible that what we call past, present, and future are the same? Might time travel as we talk about it only be a case of how to find and travel the proper curved-space path?
I hope these are worthy questions or at least bring forth worthy thoughts to ponder.
Well I don't know who "me aki l " is, but I thought this was a blog comment area, not a playground for making anagrams. Tru, the name when abbreviated is "Aki", but I think somebody somewhere has his head mixed, as I am Miss Lim Kae, an American.
Miss Lim Kae: I do Apologise. Maybe I should moderate the comments through my email first.
Where in The States are you from Miss Kae?
Hello Kae Lim. I too am an American. I do not profess to be well versed in Relativity, be it Special or General Relativity, although I own and read books on this and related subjects. I do not have the mathematical or educational qualifications to speak on a high level on the subject. So, do not be off-put by some of my off-the-wall responses and questions.
My goal is to learn a bit and to try to pose a worthy question or offer a worthy thought from time to time. I get real joy out of seeing the comments of intelligent people who do understand the subjects posed here. So, as a fan of this blog, I welcome a fellow American with a higher understanding than I have.
Perhaps, I for one, do need some editing when I come here. An innocent comment you made even led me to think Dave H was onto something, so do forgive us. Thankfully I had my own comments, which may not even measure up to a good anagram. However, I would rather read more of your thoughts, if you will be so kind to return and share them with us. I look forward to both Aki and Kae Lim's future comments. Yours too Dave H.
Interesting that an anagram of
"Dave h" is a Yiddish Sith,
Darth "Vadeh"
David Harris, it was very nice to meet you and get to know you through your many comments here. If you do not return, then I must say I will miss your many comments. Thank you for sharing your thoughts. May your destiny be a nice one filled with many pleasant memories. Also, may God bless and keep you, whatever your beliefs may be. I found you honest and sincere here. Bye-bye David my friend.
Wyman, Sir, you are a Diamond
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