Space-time confusion

  • #1

Main Question or Discussion Point

Hi.

I don't mean to sound stupid but I'm quite new to learning about space but I'm real hooked on understanding how it all works. One thing that I come across alot is Space-Time...I'm really not sure that I understand how it in itself works...How something can move in a different time if it moves faster etc...I've tried to find documentaries that would help but am finding it difficult to find something specific to space-time itself. Can anyone suggest anything I can watch online or download that would clear this cloud in my mind?!?

mAGPIe
 

Answers and Replies

  • #2
Wallace
Science Advisor
1,249
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How is this for a simple analogy;

You have to accept first that everything has a fixed total space-time velocity. Let's apply this to regular 3 dimensional space. Say you are travelling and 100 Km/h due east. Your total velocity is 100 km/h. Now lets say you turn a bit so that you are going north-east. Your easterly velocity has become smaller, and your northerly velocity had increased from zero to some value. If you work out the total velocity, you still get 100 km/h.

Now, the trick with space-time is that in addition to the components of velocity in space (i.e. dx/dt, dy/dt, dz/dt) you also have a component in time (dT/dt). If you're not moving with respect to space, then you are just moving in time. Once you start to move in space, say you pick up a component dx/dt, then your component dT/dt becomes smaller to compensate, such that your total '4-velocity' stays constant.

For my two time co-ordinates, t is your time, the time on your watch, and T is the time that someone who is stationary with respect to the x,y,z co-ordinates observers you to have. So if you move with respect to someone, they see your time go slower than theirs.
 
  • #3
11
0
How is this for a simple analogy;

You have to accept first that everything has a fixed total space-time velocity. Let's apply this to regular 3 dimensional space. Say you are travelling and 100 Km/h due east. Your total velocity is 100 km/h. Now lets say you turn a bit so that you are going north-east. Your easterly velocity has become smaller, and your northerly velocity had increased from zero to some value. If you work out the total velocity, you still get 100 km/h.

Now, the trick with space-time is that in addition to the components of velocity in space (i.e. dx/dt, dy/dt, dz/dt) you also have a component in time (dT/dt). If you're not moving with respect to space, then you are just moving in time. Once you start to move in space, say you pick up a component dx/dt, then your component dT/dt becomes smaller to compensate, such that your total '4-velocity' stays constant.

For my two time co-ordinates, t is your time, the time on your watch, and T is the time that someone who is stationary with respect to the x,y,z co-ordinates observers you to have. So if you move with respect to someone, they see your time go slower than theirs.
Would this not result in a linear decrease of dT/dt instead of what is experimentally observed? A chart of of speed vs time will show small decreases in dT/dt until very close to the speed of light at which time dT/dt decreases rapidly.
 
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