
#1
Dec3007, 08:54 PM

P: 9

hi
I read a few other post about this but i'm an engineer, not a physicist, not a genius and didn't get much wiser. And if it's possible try not to use to many technical terms when you answer this, please. As it says in the title "time slows down when you approach the speed of light", it's driving me crazy. I watched a documentary on Discovery about the 100 greatest physics discoveries and it was a bit superficial. They said that...
Some literature says that it has been exsperimentally confirmed but not how. I just don't understand, maybe because how i think of time... i see time as a man made thing, if humans cease to exist time has no meaning or also cease to exist. This doesn't mean that all the processes in the universe stops. Like lenght for exsample, what's the meaning of a cm or meter if there are no humans or marketing for that matter, etc. So why would the processes in your body slow down (and you would age at a lower rate) just because you're moving extremely fast? 



#2
Dec3007, 09:14 PM

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Mass, length and time all depend on relative motion.
If you move fast your mass, size and measurement of time differ compared to a stationary observer. It might not be obvious but it is true! It has been experimentally verified in a number of ways, unstable particles created in upper atmoshpere reach the surface but don't live long enough to do that  unless time for them is slowed down. The clocks in GPS satellites have to be adjusted to take this effect into account (actualy it's more complicated because they are slowed down by their speed = special relativity, and speeded up because of the lesser gravity = general relativity) 



#3
Dec3007, 09:18 PM

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Remember this is "relativity"! You can only "near the speed of light" relative to some other frame of reference. If you speed up relative to another frame of reference, people in that frame, watching you would see your clocks, bodily functions, etc. slow down. You would not notice any change. In fact, since "speed" does not have a direction, you would see their clocks, bodily functions, etc. slow down. And, while it is true that such units of measure as "second" or "cm" or "meter" are 'manmade', time and distance are not. If humans ceased to exist, animals and plants would still be born and die. THAT'S what time is.




#4
Dec3007, 09:47 PM

P: 131

time slows down when you approach the speed of light? 



#5
Dec3007, 10:39 PM

P: 15,325





#6
Dec3107, 06:03 AM

P: 1,504





#7
Dec3107, 07:09 AM

P: 9

thank you all for your replies... i'm still a bit confused thought, but i'm going to read some books once my exams are over.
i just have one last question... does special relativity hold true for an electron and other quantum mechanical systems? just a note: all this started when i wanted to explain the electrical properties of carbon nanotubes in depth. I started at Bohr and Einstein and at that time relativity didn't seem to matter, but now i'm back at relativity. 



#8
Dec3107, 08:27 AM

P: 1,504

Anyway, just to say three things: 1. the magnetic field generated by an electric current is a relativistic effect of charges's movement; 2. electrons in an accelerator obeys special relativity laws; 3. the electron's spin (and all the consequences of it e.g. Pauli's principle, the way atoms are made; magnetization of matter) comes from Dirac Equation which is the relativistic generalization of the Schrodinger equation for the electron. 



#9
Dec3107, 09:19 AM

P: 9

thank you lightarrow.
i was hoping it wasn't, it would have made life easier. I started with a book on quantum mechanics and as i incountered subjects i had little or no kwonlegde of i read about them. I know i still lag knowlegde about quite alot of physics subjects, so please bare with my stupid questions. OH... and happy new year everyone 



#10
Dec3107, 11:25 AM

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#11
Dec3107, 01:38 PM

P: 14

For further reading on the subject of time and it's complexities I would suggest "About Time" by Paul Davies. It's an excellent book and Mr. Davies is very good at explaining the complexities of time in an easy to understand writing style.




#12
Dec3107, 04:09 PM

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These are maps, of course, where time is represented by a spatial dimension. The map represents the territory, but the map is not the territory. Now, in the twin paradox, the two twins will draw a triangle. One twin, who does not accelerate, draws a "straight line". The other twin, who does, draws two different straight lines  sides of the triangle. On these diagrams, it is important to know that the time elapsed by a clock following a particular path through spacetime between two events will be represeted by a "length" function related to the "length" of the path. The "length" is, however, not measured in quite the usual way, it is computed by the formula for the timelike Lorentz interval. This means that one takes dt^2  ds^2 as the interval squared, where dt is the time interval, and ds is the space interval. This is very similar to the pythagorean theorem, but different because of a minus sign. On the plane, there is an identity known as the "triangle identity" that says that the shortest distance between two points is a straight line. So if you have a straight line connecting two points, it will be shorter than a path that follows two sides of a triangle. In spacetime, the twin paradox says that the longest time interval between two points is a straight line. This has also been called the principle of maximal aging, or sometimes extremal aging  google for some recent posts about this. (I'll post the link if needed). This principle of maximal aging is analogus to the way the shortest distance between two points is a straight line. So some of the details are involved, but the end result is simple. In *flat* spacetime (this works in SR, not in GR), the twin that follows a straight line on the spacetime diagram is the one who experiences the most proper time. The twin who follows a different course takes a shorter amount of proper time. 



#13
Dec3107, 06:41 PM

P: 9

ok, so it wasn't my last question. I may have been taking the "relative to the observer" part a little to lightly.
but first thank you dbecker for telling me about that book. Everything is relative, right? If there was a space that is completely empty, no vacuum and no background radiation, just complete nothingness and you place one object in that space. I first thought that it would not be possible to move at any speed because it would be relative to nothing, but wether or not that space is infinite or finite and no matter what its shape might be that object will always move relative to the center of that space, right? And even if you remove that object and wether or not the space is constant or expanding, then the space would still be relative to its own center. 



#14
Jan108, 10:45 AM

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#15
Jan108, 11:27 AM

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#16
Jan108, 03:55 PM

P: 9

thank you Ivy... i think i got a bit too philosophical.
what i really wanted to ask was just "is there anything i the real/physical world that is not relative", cause i can't think of something that isn't. Anyway none of you have to be more specific than yes or no, but if yes you could provide just one exsample. And at least for my sake that will be the end of this thread. I have read about more stuff, the last couple of weeks, than my brain can contain in such sort time, i can hardly remeber a page at time right now. Thanks to all who have helped in this thread. 



#17
Jan108, 08:01 PM

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Well, in a sense, while velocity is "relative" to some frame of reference, acceleration is not! If you feel a force, given by F= ma, then you will feel a force in any frame of reverence. Of course, if you are will to ascribe that force to some outside influence, such as "gravity", then acceleration is "relative" again!




#18
Jan108, 11:06 PM

P: 3,967

Here is something to ponder. With just one object in an empty universe it would be impossible to tell if it had linear motion or not. However it would be possible to tell if that lonely object was spinning or not. If you had just 2 objects in our otherwise empty universe it would be impossible to tell which one was stationary and which was moving. However, if one of the objects was spinning, you would be able to tell which one is spinning. For practical purposes assume an object is a large body that holds an observer who has a light source, clocks, rulers, mirrors and a few other bits of lab equipment to make measurements with. 


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