Is Time Travel Possible ?
What is Time Travel ?
Time travel is the concept of movement between certain points in time,
analogous to movement between different points in space by an object or a
person, typically with the use of a hypothetical device known as a time machine.
Although humans can't hop into a time machine and go back in time, we do
know that clocks on airplanes and satellites travel at a different speed than
those on Earth.
We measure the passage of time in seconds, minutes, hours and years, but this doesn't mean time flows at a constant rate. In fact Einstein's theory of relativity determines that time is not universal. Just as the water in a river rushes or slows depending on the size of the channel, time flows at different rates in different places. In other words, time is relative.
But what causes this fluctuation along our one-way trek from the cradle to the grave? It all comes down to the relationship between time and space. Human beings frolic about in the three spatial dimensions of length, width and depth. Time joins the party as that most crucial fourth dimension. Time can't exist without space, and space can't exist without time. The two exist as one: the space time continuum. Any event that occurs in the universe has to involve both space and time.
We all travel in time! We travel one year in time between birthdays, for example. And we are all traveling in time at approximately the same speed: 1 second per second.
We typically experience time at one second per second.
NASA's space telescopes also give us a way to look back
in time. Telescopes help us see stars and galaxies
that are very far away. It takes a long time for the light from
faraway galaxies to reach us. So, when we look into the sky with a telescope,
we are seeing what those stars and galaxies looked like a very long time ago.
However, when we think of the phrase "time
travel," we are usually thinking of traveling faster than 1 second per
second. That kind of time travel sounds like something you'd only see in movies
or science fiction books. Could it be real? Science says yes!
This image from the Hubble Space Telescope shows galaxies that are very
far away as they existed a very long time ago.
How do we know that time travel is possible?
More than 100 years ago, a famous scientist
named Albert Einstein came up with an idea about how time works. He called it
relativity. This theory says that time and space are linked together. Einstein
also said our universe has a speed limit: nothing can travel faster than the
speed of light (186,000 miles per second).
Einstein's theory of relativity says that space and time are linked
together.
What does this mean for time travel? Well,
according to this theory, the faster you travel, the slower you experience time. Scientists have done
some experiments to show that this is true.
For example, there was an experiment that used
two clocks set to the exact same time. One clock stayed on Earth, while the
other flew in an airplane (going in the same direction Earth rotates).
After the airplane flew around the world,
scientists compared the two clocks. The clock on the fast-moving airplane was
slightly behind the clock on the ground. So, the clock on the airplane was
traveling slightly slower in time than 1 second per second.
Can we use time travel in everyday life?
We can't use a time machine to travel hundreds
of years into the past or future. That kind of time travel only happens in
books and movies. But the math of time travel does affect the things
we use every day.
For example, we use GPS satellites to help us
figure out how to get to new places. (Check out our video about how GPS
satellites work.) NASA
scientists also use a high-accuracy version of GPS to keep track of where
satellites are in space. But did you know that GPS relies on time-travel
calculations to help you get around town?
GPS satellites orbit around Earth very quickly at about 8,700 miles (14,000 kilometers) per hour. This slows down GPS satellite clocks by a small fraction of a second (similar to the airplane example above).
However, the satellites are also orbiting Earth about 12,550
miles (20,200 km) above the surface. This actually speeds up GPS
satellite clocks by a slighter larger fraction of a second.
Here's how: Einstein's theory also says that gravity curves
space and time, causing the passage of time to slow down. High up where the
satellites orbit, Earth's gravity is much weaker. This causes the clocks on GPS
satellites to run faster than clocks on the ground.
The
combined result is that the clocks on GPS satellites experience time at a rate
slightly faster than 1 second per second. Luckily, scientists can use math to
correct these differences in time.
Did you know your GPS devices rely on time-travel calculations to help you navigate around town? It's true! GPS satellite clocks are about 38 seconds longer per day than a clock closer to earth due to the gravitational frequency shift. They make up for this discrepancy by using time travel calculations or they could be way off from your current location and time.
The speed of light plays a decisive role in time travel
It is precisely this condition that plays a decisive role in the question of whether time travel is possible. The law of causality follows from the fact that nothing can be faster than the speed of light. The law states that the effect of an action can only occur after the cause, which would make time travel into the past impossible. "For me to travel back in time and set in motion events that prevent my birth is to put the effect (me) before the cause (my birth)," explained Millington.
If scientists didn't correct the GPS clocks, there would be big problems. GPS satellites wouldn't be able to correctly calculate their position or yours. The errors would add up to a few miles each day, which is a big deal. GPS maps might think your home is nowhere near where it actually is!
Is time-travel into the future possible
according to Einstein's theory of relativity?
Albert Einstein postulated within the framework of his theory of relativity that light always moves at the same speed in a vacuum. From the constancy of the speed of light it follows, however, that space and time must not be absolute, but relative. A direct consequence of this is that time passes at different speeds depending on how fast objects move. For example, a moving clock in a car moving at a constant speed ticks more slowly from the point of view of a resting observer who is not in that car.
Time travel is possible based on the laws of physics, according to new calculations from researchers at the University of Queensland.
Time travel is theoretically possible, new
calculations show. But that doesn't mean you could change the past. It means
time-travelers wouldn't be able to alter the past in a measurable way, they say
— the future would stay the same.
The grandfather paradox
Still,
physicists continue to struggle with scenarios like the corona virus example
above, in which time-travelers alter events that already happened. The most
famous example is known as the grandfather paradox: Say a time-traveler goes
back to the past and kills a younger version of his or her grandfather. The
grandfather then wouldn't have any children, erasing the time-traveler's
parents and, of course, the time traveler, too. But then who would kill Grandpa
?
Time travel into the future through wormholes
An illustration of an
Einstein-Rosen bridge, or wormhole in the fabric of space.
Wormholes are a hypothetical warped space-time permitted by the Einstein field equations of general relativity.
However, as Stephen Hawking writes in his book, there could be a way time travel into the past may be possible: wormholes that connect two distant places in the universe.
In Einstein's general theory of
relativity, gravity is a consequence of the way in which mass warps space and
time — mass distorts space-time and this in turn influences the movement of
mass. In physics, space-time refers to the joint representation of
three-dimensional space and one-dimensional time in a four-dimensional
mathematical structure.
"The
more mass we squeeze into a region of space, the more spacetime is warped and
the slower nearby clocks tick. If we squeeze in enough mass, spacetime becomes
so warped that even light cannot escape its gravitational pull and a black hole
is formed," wrote Millington.
However, only the edge of this
black hole is pertinent when it comes to time travel: there, time passes
infinitely slowly relative to a distant observer: your clock would tick
infinitely slowly relative to those far away from it. Physicists assume that
wormholes can be formed from black holes.
Wormholes are a kind of tubes in
space-time that make it possible to get from A to B at the speed of light. In
order to stabilise such a tunnel, however, locations with a negative spatial
curvature, i.e. a negative energy density, would be required. But can an energy
density become negative at all?
Most people would answer this question with a resounding "no", if basing their answer off the classical physics of the 19th century. The modern theory of quantum mechanics, however, doesn't exclude the existence of negative energy densities: empty space is not empty, according to quantum mechanics.
Movies about time travel:
- Planet of the Apes (1968)
- Superman (1978)
- Time Bandits (1981)
- The Terminator (1984)
- Back to the Future series (1985, 1989, 1990)
- Star Trek IV: The Voyage Home (1986)
- Bill & Ted's Excellent Adventure (1989)
- Groundhog Day (1993)
- Contact (1997)
- Galaxy Quest (1999)
- The Butterfly Effect (2004)
- 13 Going on 30 (2004)
- The Lake House (2006)
- Meet the Robinsons (2007)
- Hot Tub Time Machine (2010)
- Midnight in Paris (2011)
- Looper (2012)
- X-Men: Days of Future Past (2014)
- Edge of Tomorrow (2014)
- Interstellar (2014)
- Doctor Strange (2016)
- A Wrinkle in Time (2018)
- The Last Sharknado: It's About Time (2018)
- Avengers: Endgame (2019)
- Tenet (2020)
- Palm Springs (2020)
- Zach Snyder's Justice League (2021)
- The Tomorrow War (2021)
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