LET’S TALK ABOUT THE FUTURE!

TIME TRAVEL - going backwards and forwards in time

has always sparked people’s imaginations.

by ”Nichita Stănescu” Highschool s eTwinning team

Time travel is a concept that has lived in the human

consciousness for thousands of years. But are such tales only

possible in the realms of science fiction and fantasy? Almost all

of us have seen one or two movies featuring time travel. The

concept of going backwards and forwards in time has always

sparked people’s imaginations.

Historically, it has always been considered nothing more than

only science fiction; however, this changed when Albert Einstein’s

theory of relativity opened the door for the possibility of time

travel. This gave us a new way to view space and time — one that

was very different from the existing picture established by Isaac

Newton.

Newton’s classical mechanics was based on the premise that

time passes uniformly anywhere and everywhere. Einstein’s special

theory of relativity, however, tells us that the flow of time is not

constant everywhere in the universe. The faster you move, the

slower time will be–until you reach the speed of light, where the

flow of time will appear to stop. This essentially proves that time

travel into the future is possible; all you need to do is ride a

spaceship that moves at a speed close to the speed of light, orbit

the Earth for quite some time, and then return. If your spaceship

moves at 95% the speed of light and you orbited Earth for 1 year,

when you return 10 years would have passed on Earth.

This theory also tells us that if you move faster than the

speed of light, you will be able to travel back in time. Of course,

as most of us might already know, nothing can go faster than

light, but Einstein’s other theory of general relativity has some

predictions that may allow us to cheat the laws of physics and

travel faster than light.

Einstein’s general theory of relativity deals with gravity and

the fabric of spacetime. In Einstein’s picture of the universe,

space and time are combined into one spacetime, and the

geometry of spacetime is affected by the matter that is in it.

Einstein showed that the fabric of spacetime can be bent,

stretched or twisted depending on the matter within it. We can

take advantage of this to be able to travel faster than light; all

we need is a rotating black hole. The rotating black hole

continuously twists the spacetime around it. Therefore, if we

could orbit the black hole at a speed very close to the speed of

light, an outside observer would see us moving at a speed faster

than light depending on how fast the spacetime is being twisted.

We are not breaking the laws of physics here, as we are not

actually moving faster than light. It is when viewed from the

outside that we will appear to be doing so, because of the addition

of velocities.

So, When Einstein first put together his theories, he

concluded that space and time are one entity instead of two

separate ones acting independently from the other. This is now

called the space-time continuum. So, we also know that light

travels at a speed that is almost perfectly constant across the

vast expanse of mostly empty space. Since photons have no mass,

they are able to travel at the universal speed limit, which

measures out to be about 300,000 kilometers per second (or

186,000 miles per second). This is what we know as “the speed of

light.” Literally, nothing (that we know of) can travel faster than

this speed.

Hopefully you’ve heard of Einstein’s famous equation E =

mc^2, which revealed one of the most profound, life-changing

discoveries of all time. You may know of it as the mass/energy

equivalence. Essentially, matter is equal to energy (they are

different expressions of the same thing). When something speeds

up, its energy will increase too since energy is equal to mass (and

vice versa). The heavier the object is, the more energy that is

required to make it accelerate. Therefore, you would eventually

need more and more energy to make the object continue moving at

light-speed.

The most interesting portion of Einstein’s theory of special

relativity probably has to be the implications of what happens to

particles traveling near or at the speed of light. It says that time

tends to go much slower for particles traveling at the speed of

light than it would for an outside monitoring the photon’s progress

from afar. Interestingly, this is one aspect of special relativity

that can be tested here on Earth! Our satellites in LEO (low-

Earth orbit) must take into account the effects of special

relativity when calibrating their onboard clocks, which ticks with

an accuracy of one nanosecond (about 1 billionth of a second).

As an example, GPS satellites are capable of determining

your exact position on Earth with an accuracy of 5 to 10 meters,

but to achieve that level of precision, the clocks on board must be

accurate to 20-30 nanoseconds. Because an observer on the

ground (in your car in this instance) sees the satellite in space in

motion relative to them, the clocks onboard will tick more slowly

than the one in your car, causing them to be off by about 7

microseconds per day due to the time dilation effect of the

relative motion of the two.

Assuming YOU were able to travel very close to the speed of

light, you would experience time much more differently than

someone observing your movement from Earth. Hypothetically,

what you would experience as a second may feel like a minute to

the observer, this is called time dilation. Theoretically, this could

make you experience time backwards, which would violate

causality (the chronological order of influence of things in the

universe) not to mention how we perceive things from the floating

rock we are chained to currently.

You’re probably wondering how this would work, but the

details are kind of fuzzy to us too since most of the laws of

physics point to this being very unlikely (if not impossible). If it

were possible, as you approached light speed, the outside universe

would begin to slow down in relation to you (or whatever else

that’s traveling at the speed of light) before it stops. For you;

that is. The observer will experience time the way they typically

do. Once you exceed light speed, the outside world would slow

down to the point that space/time would be moving backwards in

relation to you.

Again, there is little evidence to suggest that faster than

light travel is possible to begin with and that’s just for subatomic

particles, which don’t have the mass that we (humans) do. If it

were, there would be some incredibly awesome implications in the

world of physics. One hypothesis postulates that it could be

possible to communicate with the past using neutrinos, which

famously invaded the news for a few months in 2011; after

physicists thought they had evidence that suggested neutrinos

were traveling just a bit faster than light speed.

As it turns out, there were issues with the equipment and

they didn’t actually observe neutrinos traveling faster than the

universal speed limit. Even if we could, it’s quite unlikely the

message would even be received since they don’t interact much

with normal matter. It is kind of humbling to note that the past is

very much a part of the universe as much as the present.

Another prediction of general relativity that we can use is

the Einstein-rosen bridge, or as it is more popularly known, a

wormhole. A wormhole is a cosmic shortcut from one point in

spacetime to another. It can be visualized by making two separate

points on a piece of paper meet by folding the paper. We should

remember that Einstein combined space and time into one so we

can use a wormhole to travel through both space and time. It is

still not certain how we can make a wormhole, and once we are

able to make one general relativity tells us that it will only last for

a very brief amount of time. Keeping the wormhole open will be

another problem.

The possibility of travelling back in time has long been

debated. Most are convinced that it is impossible because of the

many paradoxes it can cause, particularly on the law of causality.

The law of causality states that the cause should always happen

before its effect. This law can be broken by backwards time

travel, as is shown by the famous grandfather paradox. If you will

go back in time and kill your grandfather, your father, and hence

you, will not be born.

If you were not born, you will not be able to kill your

grandfather, hence, you will be born, and you will be able to kill

your grandfather, and so on… Another paradox concerns the

passage of information from one time to another. Let’s say that

we go back in time and teach the young Isaac Newton all the laws

of physics that he himself discovered. Now, where did those laws

come from? We can no longer say that it came from Newton

because we taught him those ideas. We, on the other hand, cannot

say that it came from us, as obviously it came from Newton.

Lastly, the easiest paradox to understand is why don’t we see

time travellers from the future? There are many more paradoxes

that we can think of with backwards time travel but fortunately,

modern physics has a solution to these paradoxes.

To resolve the paradox of going back in time, some physicists

say that if you were to go back in time, you would arrive in the

past of another universe. So, when you go back in time, you will

arrive in another timeline, a timeline that you can be able to

affect in every way without causing paradoxes. This theory of

parallel universes arises from the probabilistic nature of quantum

mechanics. In quantum mechanics, you cannot tell the specific

position of a particle, rather you can only compute for the

possibility that it will be in a specific place.

Every one of those possibility happens, not in our universe

but in another universe. In fact, this theory tells us that there

are an infinite number of parallel universes, one of which may have

me inventing an iron man suit, or another in which you are Batman.

According to some, time travel is slowly becoming a reality.

If we are somehow able to travel through time, we could become

masters of the universe (or very nearly so). The philosophical and

scientific basis for time travel is still being debated upon, but

once we do invent a time machine (and I’d like to think it is at

least possible that we will), it will be the most important discovery

of humankind.

Source: http://en.wikipedia.org/wiki/Albert_Einstein

http://en.wikipedia.org/wiki/The_Einstein_Theory_of_Relativity

http://einstein.biz/