Some of us believe time travel is possible.  They believe Albert Einstein had open the door to traveling back though time we can change history. It opens the door to the possibility of the famous grandfather paradox. What if we go back in time and killed our grand parents? Would we exist?  Could it be possible time loop of the situation exist?

Try to explain were you was when your parents ( or grandparents if you like ) were little. Explain where people not born yet in the present. Explain why we can't be the age we were several years ago in the present or several years older we are going to be in the present

Explain why jet aircraft can't fit in with world war one. Try to explain why Microsoft's Windows 8 personal computer operating system could never belong 25 years ago. Try to explain why future technology won't fit the present. People and technology that fit past eras, present and future tells us there is a distinction between the past, present and future.

So how is the present measured. If you thinking our brain, sure it has the ability of measuring time. We can appreciate fully alert knows the passing of every second. It is true brain injury patients time has a limited distinction. Memory often reduces minutes to hours, days even weeks mere moments. Time is meaningless in a coma. A long time unconscious is a state of the last time remembering being conscious seems a moment ago. The point is a alert brain knows all about every second of time passing.

Lets see how an alert brain measures time. Being alert agrees  the next second to come is shifted into the present by the time you finished this sentence now the past second. It is clear every second travels from the future, present and past to an alert brain.

Our brain is pretty good at measuring a meter taking a step and a half forward. It is the time we say one thousand and one, the time second hand of analogue clocks moves a division, the time second of digital time pieces tick and light travels a distance of just under 300,000km. ( Or a 186,000 miles if you like ).

A light second is the distance light travels. Alertness agrees a minute is really 60 second  periods in the present minute. Our brain recognizes a minute is only a matter of traveling a distance light travels sixty light seconds. Our mathematical instinct agrees light travels distance of light seconds in an hour, a day, month, year, century, milliner, ( thousand years ) million, or billions of years.

Our brain recognizes the distinction of science and sports coaches making athletes win or lose by fraction of seconds in the present time. We all hear TV motor sport commentators and car shows announce lap times and nose to tail following distance dramas in less than seconds  pronounced decimals points.  For example 0.25 is a quarter second, 0.33333......... is a third,   0.5 is a half,  0.666666........ is two thirds and 0.75 is three quarter second considered quite critical.

Light traveling a fixed distance every second is a time factor measures distances in time. It obeys Newton's first law of motion once set in motion continues in that motion indefinitely in light's case in the zero resistance of out of space coasts at a maximum speed limit of just under a distance of three hundred thousand kilometres ( or a hundred and eighty thousand miles if you like ) by the time our time measuring our devices records every second.

Our brain recognizes the amount of time the second hand of analogue clocks move a division the seconds of digital time pieces, we walk a meter and we say one thousand and one. In other words to our brain agrees every one of those periods equals the distance light travels we can honestly say a light second: the distance light travels in second. Our mathematical instinct aggress in principle the maximum speed limit is indeed a perfect mathematical constant symbolized c.

Despite the zero resistance of space it coasts no faster. No matter how fast we travel the constant velocity in out of space is always maxed out to three hundred thousand kilometres every second no matter how long any other period. If we are to chase light to catch up with it The constant ( c ) remains the maximum speed limit. It is always a distance of three hundred thousand kilometres ( or a hundred and eighty thousand miles if you like ).

In 1905 Albert Einstein realized if we are to catch with light is closing the distance we travel. The second is altered with us. If we reach light speed we would be traveling in parallel with it. Our mathematical instinct agrees If we do the math's on this tells zero distance. Math's indicate if we travel faster light would be be behind us. We would be in a dimension of space and time light does not yet exist in yet.

Ten years latter during the second year of world war one star and planet gravities, ( as the atmospheres, the clouds of dust of nebulas and gas planets ) slows the passage of light. It takes longer to travel the same distance in gravity than in a lot shorter time  in the zero resistance of a vacuum. ( Deep space if you like ). The slower it goes the longer it takes to travel the  distance it travels at it maximum. In other words if light was twice as slow it would travel three hundred thousand kilometres in two seconds ( Or a hundred and fifty thousand kilometres in a second ).

Light has to travel though the resistance of the atmosphere slows it down. Enough solidness stops dead in it's tracks. In less than a second it reverses direction traveling back out of the earth's atmosphere. The resistance of the earth's atmosphere gets less and less at more and more altitude speeding  back up finally reaching the maximum distance constant in out of space.

Children's science and technology library books on light  is perhaps the simplest explanations of how light deflects. Think of a shop window pane reflection. Observations of a street reflection can be a right angle.

Light from the moon we see is nothing more than the origin of the sun's light deflecting an image of it like a straight mirror in the direction of earth. Although the moon varies in distance it is over a light second away. Our mathematical instinct agrees if we do some arithmetic on this taking less than a couple of seconds multiplied by c gives the us the distance. Our mathematical instinct recognizes the law of mathematics allows us with a known distance and c we can protect how many light seconds away from earth.

Our instinct agrees at maximum coasting since there is sixty seconds in a minute traveling at a fixed distance every second the distance light travels in a minute is merely a simple calculation of sixty times c every second.  We can honestly say the distance light travels at maximum velocity in a minute is a light minute: the distance light travels in a minute. Our math's instinct will agree sixty light seconds of distance.

Light takes eight light minutes to reach our eyes from the sun. This means the sun is a distance of only eight light minutes away. In real time light is three hundred thousand kilometres above the sun's surface by the time you finish this sentence. We don't see this light till eight minutes into the future. Our mathematical instinct agrees the distance from the sun to earth ( in terms of kilometres or miles what ever you prefer ) is sixty times eight times c.

Current light we see every second is nothing more than light's image of the sun as it was eight minutes ago every second. It is three hundred thousand kilometres ( or a hundred and eighty six thousand miles if you like ) away from earth by the time you finish this sentence every second of time as well.

Our mathematical instinct agrees the fixed constant is sixty times sixty ( or sixty squared ) equals three thousand six hundred seconds times c the distance light travels by the time a one hour TV program.

Clocks change the western calendar date every twelve midnight. Our mathematical instinct agrees if we start with the first second past midnight to the date changes again is sixty squared times twenty four giving us a total of every eighty six thousand four hundred seconds the date changes. The distance light travels in that time is all those seconds times c.

In other words every time clocks changes the date is eighty six thousand four hundred periods additions of a fixed distance of just under three hundred thousand kilometres of time.

Mathematics tells our math's instinct the reciprocal of c every second is eighty six thousand four hundredth of the date change period. Our math's instincts agrees proof when we multiply a hundred and eighty six thousandth by a hundred and eighty six thousand equals one a date change period. In other words a light day.

We can project from known distances the planet of our solar we can project them in light days away at light speed.

Operating on the same principle we can add up the first second twelve midnight Monday morning though every day of the week to the first second of the following twelve midnight Monday morning times c the distance light travels in a week. In other words a light week. We can project from known distances planet of the our solar system in terms of weeks away at light speed.

The western calendar divides up mouths into different days. They vary from as little as twenty eight to as much as thirty one. We are open to project how many moths a planet of our solar system is away at light speed.

However our mathematical instinct whole heartily agrees we can project all the seconds in a year by sixty squared times twenty four times three hundred and sixty five days of the year. Times c projects the distance. ( In terms of kilometres or miles which every is preferred ).We end up with a figure over thirty one million seconds the distance light travels familiarly known to all of us as a light year.

Calculating for the distance light travels in a decade we need to take into account of the extra day at the end of every February every third leap year. Taking into account of all the leap years in a decade we can deduce the distance in years the equivalent light years, light travels in a period of a decade.

Operating on the principle we can deduce the years equivalent of light years the distance light travels in a century, a milliner ( a thousand years ), a million years, a billion even trillions of centuries of time passes on earth. The earth is only a little more than several million centuries old. Those into challenging mathematics can convert years to centuries and vice versa centuries to years of time passes on earth.

The point of the first light from the big bang that has supposed to have created our universe is only just over fourteen and a half light years away from earth. Those into challenging math's can challenge themselves to work the time of the big bang in terms of  in simple equivalent years converting to centuries to the astronomical unit parsecs.

In the meantime we can only ponder on how far away from earth the opposite direction away light has traveled from earth. For all we know it may have already reached equal distance away ages ago.