The document explores the concept of time from both Newton's and Einstein's perspectives, contrasting absolute time and space with the relative and interconnected nature of spacetime. It discusses how time is perceived differently depending on the observer's motion, as well as the effects of gravity on time, including time dilation. Additionally, it touches on the philosophical implications of time as an illusion and the arrow of time dictated by entropy.

1. Relative time : What its all about?

2. content
• Time
• Newton's and Einstein's view of time
• Spacetime
• Illusion of past present and future
• Time and gravity
• Arrow of time

3. TIME
• Time, as a physical quantity, reminds us of duration,
measuring instruments – sand clocks, watches,
atomic clocks.
• Time is a thing that everybody knows until you ask
him to tell about it how it works etc
• One way to know about time is measure it using
some repetitive process

4. Very first clock

8. Emit light for 9192631770 times in 1second

9. Different clocks
• Clocks tell us what time is but haven't been
able to tell us what time itself is?
• Rise of train travel played key role for one of
the most startling discovery about time
• Earlier each town has its own time

11. Newton`s view about time
• I don't define time space motion as are well
known to all absolute space and time in its
nature without reference to anything external
remains always similar and unmovable
- Naturalis Principia by Newton
• Time exist in and of itself flow equally without
reference of anything external
- Principia

12. 12
What Is Absolute Space?
• Infinite, unchanging, 3-dimensional “box”
• Existing as a substance independently of
material objects and the spatial relations
among them.


15. Street and avenue are making some angle and rest
both are same and equally valid
There is nothing like absolute street and absolute
avenue but still absolute space

16. Einstein`s view
• Time is not universal its individual
• Velocity of light is constant with respect to
anything and everything
• Neither time nor space is absolute but
spacetime is absolute
• Motion in space effect motion through time
and vice versa

17. Speed of light is constant

18. Rest and motion

19. Space-time
• Spacetimes are the arenas in which all physical
events take place—an event is a point in
spacetime specified by its time and place
• A region of space consider over the
interval of time is region of
spacetime

20. Two dimensional space-
time diagram, i.e 3-D

23. Spacetime diagrams are like traditional position-time
diagrams BUT time goes vertically by convention.
So as time passes things are ‘copied up’:
space
time
Same point in
space at
different times
Standing Still
1)
2)
3)
space
time
Running
Different points
in space at
different times
1)
2)
3)
space
time
1)
2)
3) The path in
spacetime is
called a
“world-line”
space
time
1)
2)
3)
Notice that
for a moving
observer
the world-
line is
slanted.

24. • The combined speed of any object`s motion
through space and its motion through is
always precisely equal to speed of light

26. Gunfight viewed by observer on train
Bang
! Bang
!
He sees both shots
fired simultaneously

27. Viewed by a stationary observer at
station

28. Viewed by a stationary observer at
station
Bang
! Bang
!
He sees cowboy shoot
1st & cowgirl shoot later

29. Viewed by a stationary observer at station

30. Viewed by a stationary observer at
station
Bang
!Bang
!
He sees cowgirl shoot
1st & cowboy shoot later

31. Time depends of state of motion of the
observer!!
Events that occur simultaneously
according to one observer can occur
at different times for other
observers

35. View by observer at rest and moving
absolute space-time

36. Every moment on the earth that ever happen and will ever happen on the universe will all
exist in this space time

37. Space-time Loaf of bread
• Einstein viewed space time as loaf of bread
• Each observer cut its slice in its own way
• Two observer having some relative velocity
with cut space time bread at some angle small
to measure

38. Now-anything happening right now
Past
Something our experience
tell had happened
Future
Things that are yet to
happen

42. People like us,
who believe in
physics, know that
the distinction
between past,
present, and
future is only a
stubbornly
persistent illusion.
-Albert Einstein

43. Time Dilation

44. Twin paradox

45. Time and Gravity
• Accelerated motion and gravity are same side
of a coin
• Suitably changing your motion you can avoid
feeling of sensation due to gravity
• Some guy falling freely will not feel gravity
• Suitable change in motion can create gravity
• Falling guy is really a frame to see accelerated
motion

46. Rubber Mattress Example
• Imagine 2 bowling balls on a mattress, on
earth
• As they roll around on the mattress, they
make dimples in its surface
• If they get close to each other, they roll into
each other’s dimples
– they are “attracted” to each other

49. Mass tells space-time how to curve
Space tells mass how to move

50. 50
Space & time are bent, or curved, by matter.
This is gravity.
Planets, moons and baseballs go
“as straight as they can.”
www.unmuseum.org

51. • All clocks run slower in a strong gravitational
field than they do in a weaker field.
• Time ticks slower near the earth than that in
empty space

52. Time and Experience
Eggs break, ice cubes melt, stars emit radiation, we record
memories of the past. And it all happens in a consistent
“direction” (from the past to the future) throughout the universe:
 The Arrow of Time.
One of the single most surprising things about the
universe is that things change!!

53. The Entropy Arrow
According to Boltzmann
Total Entropy always increases
(The 2nd Law of Thermodynamics)

54. The CPT Theorem
CPT = “Charge-Parity-Time”
If the charge of all particles in universe were
changed to the opposite charge (so that all particles
change to their antiparticles); & at the same time, all
were reflected in a mirror; & at the same time,
time started to run backwards:
This new world would be indistinguishable
from the old world.

55. • For law of physics to tell anything we need
initial condition
• But for time initial condition is big bang,
deepest mystery yet to be uncovered

56. "Put your hand on a hot stove for a minute, and it
seems like an hour. Sit with a pretty girl for an hour,
and it seems like a minute. THAT'S relativity.”
-Albert Einstein

57. Thanks !!!