Relative time : What its all about?

content

• Time

• Newton's and Einstein's view of time

• Spacetime

• Illusion of past present and future

• Time and gravity

• Arrow of time

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

Very first clock

Emit light for 9192631770 times in 1second

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

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

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What Is Absolute Space?

• Infinite, unchanging, 3-dimensional “box”

• Existing as a substance independently of material objects and the spatial relationsamong them.

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

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

Speed of light is constant

Rest and motion

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

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

Spacetime diagrams are like traditional position-time diagrams BUT time goes vertically by convention.

So as time passes things are ‘copied up’:

space

tim

e

Same point in space at different times

Standing Still

1)

2)

3)

space

tim

e

Running

Different points in space at different times

1)

2)

3)

space

tim

e

1)

2)

3) The path in spacetime is called a “world-line”

space

tim

e1)

2)

3)

Notice that for a moving observer the world-line is slanted.

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

Gunfight viewed by observer on train

Bang! Bang

!

He sees both shotsfired simultaneously

Viewed by a stationary observer at station

Viewed by a stationary observer at station

Bang! Bang

!

He sees cowboy shoot1st & cowgirl shoot later

Viewed by a stationary observer at station

Viewed by a stationary observer at station

Bang!Bang

!

He sees cowgirl shoot1st & cowboy shoot later

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

\View by observer at rest and moving

absolute space-time

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

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

Now-anything happening right now

Past

Something our experience tell had happened

Future

Things that are yet to happen

People like us,

who believe in

physics, know that

the distinction

between past,

present, and

future is only a

stubbornly

persistent illusion.

-Albert Einstein

Time Dilation

Twin paradox

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

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

Mass tells space-time how to curve

Space tells mass how to move

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Space & time are bent, or curved, by matter.

This is gravity. Planets, moons and baseballs go

“as straight as they can.”

www.unmuseum.org

• 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

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!!

The Entropy Arrow

According to Boltzmann

Total Entropy always increases(The 2nd Law of Thermodynamics)

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.

• 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

"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

Thanks !!!