Question

what is time ? explain space-time continuum.

Answer 1

#TIME :
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time is :
• 'indefinite and progressively ongoing entity' means God knows when it was started and when it ll end .
• 'irreversible' means it always go from past to future through present .
( then how we make Time Machine O_O ) and it enables us to sequence EVENTS in order .
• WHAT A CLOCK READS
• one of the seven fundamental quantities having standard unit - second denoted by 's' .
The second : ( NCERT EXTRACT) :
it is the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of Cs-133 atom.
// it is illegal to modify this definition. ;)
• considered as 4th dimension dealing with spacetime .
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#SPACETIME
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It is made of two words - space+time - meaning that "space " and " time" are not different entities but somewhat related and mixed .
Let's take an example ;

One of my enemy wants to blow off my House by using a bomber plane . My friends living their finds it out and exchanged every bomb with a "cola can" by covering it with a bomb like box .
( they wanted to gift me some cola cans but unable to do .. now they got a golden chance ;) )
Now enemy set out with the cola bomber and ejected first cola bomb when it was at position A . It will trace a path via B & C to reach at my home.
# Path of cola bomb in Enemy's FRAME OF REFERENCE :
It will be stationary ( just decrease its size) so to enemy all points ( A,B ,C, and my sweet home) lie at the same point in space ( reference to cola bomb) appearing one after the other ( first A then B and so on ) . ( he was looking down ) .
So according to him there is no variation in space with the time ( means no spacetime variation) .
# For an observer at the ground : in his frame of reference the cola bomb traverse a parabolic path . And for him Points A ,B, C and my sweet home ) have their fixed positions in space .
but the time is also varying .
let's say :
bomb ll be at A at time t1 ( Event 1)
bomb ll be at B at time t2 ( Event 2)
bomb ll be at C at time t3 (Event 3)
bomb ll be at my home at time t4 . ( Event 4)
The space of cola bomb is changing with time . We have written "space" and "time" together "Spacetime variation " is there from point to point . However enemy can't observe it .

According to Einstein 's theory of relativity both the Enemy and the observer at the ground are right in their relative FRAME OF REFERENCE . But for Enemy no spacetime variation But there is for Observer at the ground .
So its a matter of Their RELATIVE FRAME whether their is purely or partially either "space " or "time " variation and or in both as SPACETIME VARIATION . These variations are continuous hence it is called Spacetime Continuum .
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hope it helps !

Answer 2

Answer:

In physics, spacetime is any mathematical model which fuses the three dimensions of space and the one dimension of time into a single four-dimensional manifold. Spacetime diagrams can be used to visualize relativistic effects, such as why different observers perceive where and when events occur differently