# Time Travel(Part 2)

The post is about the progress in our understanding of time and the possibilities of time travel in our modern world.The effort is to provide the basic idea without the rigorous mathematics and terms.

So,in previous post we came to know that the space which we see as nothing is actually effected by the presence of  mass or energy.Greater mass means greater will be the warping of space and since gravity is nothing but this curvature of space so greater will be the gravity...it is an effect originated from the curved geometry of space.
In short
Heavy mass--->more warping of space--->strong gravity.
It can be easily realized..among planets,Jupiter is the heaviest planet in solar system..so it warps more space than other planets and hence it has the strongest gravity.Similarly Sun is more heavier than Jupiter thus it will warp more space around it therefore strong gravitational pull.

Since both space and time are linked with each other(known as space-time)the distortion in space also results in the distortion of time.Greater the warping of space slower will the passage of time.
Now,
Heavy mass--->more warping of space--->strong gravity--->slower passage of time.

While discussing time dilation of special relativity we understand that the faster we move,slower will be passage of time and also the space will be contracted.These effects(effects discussed in SPECIAL RELATIVITY) are relative i.e you,moving in car,will say people on ground are moving slowly and are contracted(since things are moving for you) while on the other hand for people on ground you are acting slowly and you along with your car have been contracted(as for them you are in motion).
Whereas  the effects of general relativity are in agreement from both the observers.

For example,suppose you travel to some other region,which has a much more strong gravity than that of earth.Now,when you again look at the grand clock on earth,you will notice that the grand clock is ticking fast while your wrist watch is ticking at the normal rate.And people on earth,observing your wrist watch will say that your wrist watch have been slowed down and their grand clock is ticking normally.
Here both are saying the same thing but the other way round.
It is because when you moved to the other region with strong gravity(i.e region of more warped space).This curved space also effect your senses and since our senses along with the space have also been distorted that is why we feel everything normal in our local region...and obscure in other,non-local regions.
Such dilation in time due to the curved space is generally called gravitational time dilation.

Einstein's theory of general relativity not only tells us about the curved space-time but it also predicts two highly fascinating objects which should exist according to the theory.
First are Black holes,which have been successfully detected and the other are wormholes.
BLACK HOLES are formed after a star dies crushing down completely under its own gravitational pull.They are highly dense..the neutrons and other subatomic particles are almost touching each other having no space between them.
To get an idea of the density of black holes...a ONE SPOON FULL mass of a super massive black hole will be much heavier than the mass of whole landmass of  Delhi.

Since Black holes are much more massive and dense... they warp the space around them to a greater extent and hence have a very strong gravitational pull.Even light can not escape the gravitational pull of black holes if it enters the event horizon.
Event horizon is the limit beyond which if anything goes,into the black hole,then it can never came back and will be crushed by black holes immense gravity.
The first image below shows the different stages a dying star passes through to become a black hole

Now since even light can not escape their gravitational pull,they appear black.

BLACK HOLES CAN BE USED TO TRAVEL FORWARD IN TIME...
If you have understand gravitational time dilation(discussed above) then it will be easy to understand.
Suppose you enter a space shuttle and travel close to a Black Hole...since you are now in a region of high gravity then time will pass more slowly for you than the time here on earth.After spending just few hours near to the black when you will return back to the earth then you will find that many years have been passed on earth.
That is you traveled to the future spending just few hours near to black hole.
However, there are no black holes present near our solar system.The nearest black hole is several light years away from earth..so just to get there requires a lot of fuel first and to spend few hours near it,without being pulled inside will require immensely powerful exhaust system..to overcome their gravity.
So going to the future is possible however it may take several years to built such highly efficient ships.

Now,what about going to the past??
This is achieved by the wormholes described by general relativity.

Wormholes are just like the tunnels connecting two different places with each other...wormholes also connect different regions of space in our universe.A wormhole simply cut short the distance between two regions of space.Since they are bridges connecting two regions so there can be different kinds of wormholes,some connecting two regions in same universe or some connecting two different universe(if multiverse exist). Wormholes are also supposed to connect different times as well.
That is if you enter a wormhole you not only be transferred to an other place but also to either to future or to the past as well.

All this seems exciting right?
But sad part is that no macro wormholes(macro here denotes big enough so that spaceships can enter it) have never been detected so far.And if they are detected in future then the physics underlying them states that they will be very unstable.So much sensitive that if anything will cause any disturbance,they will collapse..closing forever.

But in June 1988,three physicist Kip Thorne,Michael Morris and Ulvi Yurtsever 'solve' for a womhole
(solve because wormholes are predicted mathematically by general relativity,they don't have any physical existence yet but they are supposed to exist),one which is stable and can be used to travel.

So it may be possible that one day these wormholes were detected and our technology become so advance that we can construct efficient ships to travel close to a black hole and to pass through wormholes.

So whatever you see in science fiction movies are often valid theoretical possibilities off physics which are yet to be verified experimentally.
Now  it's all folk regarding the time travel..Time travel is not possible with today's technology but may be in a distant future it may becomes the reality.

So,if we happened to travel back in time..can we change the past?overturned history completely?rectify our mistakes done in past?....in next post.

# Time Travel(Part 1)

The post is about the progress in our understanding of time and the possibilities of time travel in our modern world.The effort is to provide the basic idea without the rigorous mathematics and terms.

Time..for general public it is the normal tick-tick-tick of the clock but for physicist it have been a great mystery from the very beginning of our understanding of nature.

Isaac Newton was the first one who gave a scientific description of time.
Well,this is not actually true,Rig Veda contain very beautiful description of time,however it also describes time as static and moving forward.But there is an another calculation in Indian ancient literature,describing the 1 day of Lord Brahma which shows that people were aware of time dilation...i will explain time dilation later.It all shows that ancient Indians have a deep knowledge than we have today about world,however most scientist don't believe the knowledge Vedas contain.
Newton also described time as something which cannot be changed,it flows like a river.You cannot change it's pace.It is like an arrow always moving forward i.e towards the future.
However,200 years later after Newton,an unknown physicist in 1905 drastically changed the all earlier accepted notions of time.A simple idea overturned the old concepts of time.Albert Einstein...with his Special theory of Relativity shows us that time is not static it changes with our movement in space and is also effected by the curvature of the space itself.Time is dynamic.Time ticks differently for different observers.

Time Dilation...in simple words,it says the faster you move the slower the time will ticks.At first it seems all logical that the faster i move the less time i will take to reach a place.But here what matters is how fast you are moving.
First consider this postulates of Einstein's theory-"Speed of light is constant for every observer"
That is if you are standing on a ground and you measure the speed of light you will measure it to be 671 million miles per hour and even if you measure the speed of light while moving in an air plane with speed 200 miles per hour then you will still measure it to be 671 million miles per hour..it will remain constant no matter you are standing or moving with respect to it.

Now,to understand time dilation,consider this hypothetical situation.Suppose you have a car which can move close to the speed of light and you are about to leave to see an old friend of yours.Before starting your journey you match your wrist watch with a grand clock tower,which is so big that it can be seen from far off places clearly.Now you start your journey..moving at 100 miles per hour things are as usual and normal.You are sitting in your car and the people are passing by you i.e you feel you are at rest and others are moving relative to you.The time(the ticks)of your wrist watch matches exactly well with the grand clock.
However in hurry to reach your friend quickly you accelerate to 400 million miles per hour.You again look at both clocks(your wrist watch and the grand clock) to make sure you are going by time. you will be amazed to see that the grand clock is ticking slower than your wrist watch,soon you will realize that it is not the clock only everything outside your car is slowing down.Peoples are walking slowly,talking slowly,eating slowly as if someone has pressed the slow motion button for outer world.This slowing down of time is known as Time Dilation.You will further realize that everyone outside the car will appear to be shrunken in width(this is known as length contraction),for you things outside car will appear to be exceptionally thin.However you perceive things in your car absolutely normal.

It is just the one side of the story.
For people outside the car you are moving with respect to them.So when they will observe your wristwatch(just assume that you can observe it at this great speed) they will find that your clock is ticking slowly compared to the grand clock and for them,you will appear to be moving slowly in your car.Also they will find that your car as well as you has shrunk in length.You will never feel it physically or mentally because both have also been effected.
The effects are relative..and both(you and people outside) are absolutely correct.It is all because....for you, inside the car,everything else is moving and you are at rest whereas for people outside car you are moving.

Now people may think that what if someone will move faster than light then...one should abandon the idea of going faster than light because relativity shows that faster you move slower the time ticks and heavier you become.That is if you accelerate your car more and more close to the speed of light, the car will become more and more heavier thereby decreasing you velocity.
Please don't think of the news of neutrinos going faster than light...it was found later that there was a flaw in their experiment which result in that result...however it may be possible that we reach that limit some day.
However their are theoretical particles,called tachyons,but they are theoretical there is no physical evidence of them yet.

10 years later Einstein published his General theory of relativity..a theory dealing with gravity.
Newton when discovered gravity doesn't himself know the true origin of gravity i.e what causes gravity.
Although,he was successful in developing the equations to calculate gravity acting between different objects and on different planets..the equation holds at every point in universe,making it an Universal Law.

This new theory,General Relativity tells us what gravity actually is.
Just like the Special theory of relativity,general theory of relativity revealed a more drastic behaviour of space and time,showing a relation between space and time..collectively known as space-time.

Space is the emptiness we see around us(not the space outside the earth) i.e. nothing but mind you this nothing isn't actually nothing it is among the major players who govern the universe.
Space is everywhere,everything exist in this space.Anything which you see as solid is actually 99% empty
(i.e contains space) because an atom which is the fundamental(not most fundamental)constituents of everything is itself 99% empty.Say for example Tajmahal,if you remove all the space from all the atoms making the Taj Mahal then it will shrink down to the size of a grain but weighing millions of ton.

The secret of gravity lies in this space.The presence of mass/energy warps the space-time around it.
To understand what it means see these images..the grids are representing the space.Since we see space as nothing..to illustrate the bending of this 'nothing' grid representation is used.

Yes this so called nothing can actually warp due to the presence of mass/energy and mass drags the space along it.

An another way of understanding,suppose you and your friend are holding a long rectangular rubber sheet stretched.Now i put a heavy metal ball on it.What will happen? The ball will warp the sheet around it,creating a depression around it.

The space behaves similar to that rubber sheet whenever mass(heavenly bodies) is present... they warp the space in the same manner the ball warp the rubber sheet.

Now whenever a heavenly body comes near this depression in the fabric of space..it follows the warp and start revolving around it.Here's pic and a video to illustrate this.

So it is due this warping of space that a planet or any other heavenly body revolves around the other.Therefore,the force of gravity is nothing but the curved (or warped) space.
The physical insight which Newton lacked about gravity is provided by Einstein.

Now,if you still find it hard to believe that  how can space be warped or curved.. then let me know you it has been experimentally verified by NASA.
ON 20th April 2004 NASA launched GRAVITY PROBE B to detect whether the warping of space described by general relativity is true or not....and to their satisfaction the probe verified the warping of space...earth is warping the space around it.

# THE GIRL CHILD

Two weeks ago,while reading the newspaper a headline caught my eyes.A baby girl was found in sewers,Ghaziabad.The place wasn't too far from my place where the baby was found,Police suspects that the girl belong to a rich family since the cloth in which she was covered was very expensive.The news drifted my thoughts to a similar incidence happened in my locality last month,i baby girl was found in temple.
It seems that despite Aamir's  effort to reduce female foeticide/infanticide,some peoples are still insensitive..such cases are still in news from all around the country.Yes,there is a change,now they don't kill they dump them like garbages...pathetic
Both the two girls were later sent to Mathura,in a child care home.
According to 2011 census and other national statistics 7,00,000 girls are missing at birth after determining their sex.
According to an another report 10 million foetuses  have been aborted in India with in past two decades.

The Directorate of Health Services,in Mumbai provides a much more scary statistics that since  2009,around 2.46 lakhs abortions have been done only in Mumbai.In much more detail
year 2011-2012(until March) about 1.11 lakh abortion have been done in Mumbai.
The problem,we all know,is thinking.The desire to have a male a child is the only reason.Why a male child?The reasons are as narrow as their minds.The show Satyamev Jayate has already proved the thing that this 'tradition' exist mostly among the respected educated class of the society.
It is a harsh reality that we live among such peoples,in a country where parents can easily kill their innocent new born because it was 'she'.