Interesting Facts About Time, The Fourth Dimension, And Time Travel
Interesting Facts About Time, The Fourth Dimension, And Time Travel
Time is perhaps the greatest mystery of all and is deeply wrapped up in our conscious experience of things. Since antiquity, time has naturally attracted the interest of philosophers and scientists determined to understand and explain its true nature. At the heart of the question is whether time is an actual reality of the physical world or simply an artificial construct of the human mind.
The pre-Socratic Greek philosopher Parmenides, for example, saw time as merely an illusion, while his contemporary Heraclitus believed the flow of time to be real and the very essence of reality itself. For Newton time was absolute and moved at a consistent pace everywhere throughout the universe, while with Einstein time became more flexible and relative in scope. Nevertheless, the concept of time continues to be one of nature’s greatest mysteries and no one has been able to fully explain exactly what it is really.
Four-Dimensional Space-Time
In the 17th Century, René Descartes (1596-1650) envisioned there to be three dimensions of space, with a totally separate dimension of time that together specify an object’s position in physical space. Simply stated, three dimensions are used to specify an object’s location/movement in space (forward-backwards, left-right and up-down), while a fourth dimension locates its position in time. This approach was adopted by Isaac Newton (1643-1727), the founder of classical mechanics, and classical physicists who saw time as an absolute, universal quantity completely independent from space. As such, early scientists used time to delineate a universal system of coordinates through 3-dimensional space.
In 1905, Albert Einstein then published his Special Theory of Relativity which was instrumental in introducing the concept of four-dimensional space-time. According to Einstein, time, space and motion all act upon each other and as an object’s speed increases, its time slows down in order to preserve the cosmic speed limit of light. This new concept merged space and time into space-time, and helped introduced a new framework for the whole of physics.
Three Dimensional Creatures
Being three dimensional creatures (possessing length, width and height), humans are unable to see the fourth dimension as our physical world is constructed within these three physical dimensions. We might feel or intuit time’s presence, but we can never actually detect it with our three-dimensional senses because it extends beyond our universe. Humans only perceive the fourth dimension of time as memories lodged at variable intervals, the result of which is our apparent perception of time moving forward in a straight line. Nevertheless, time exists as a dimension and objects cross it in a similar way as they do the others, although three dimensional humans are only able to move in one direction forward through time. If we could see an object’s fourth dimensional space-time (or world-line) it would resemble a spaghetti-like line stretching from the past to the future showing the spatial location of the object at every instant in time.
Space And Time Inseparable
Also, in accordance with Einstein’s general theory of relativity, a massive object in space distorts the fabric of both the space and time around it. In other words, gravity is actually the result of mass stretching its surrounding space-time. For example, our Sun’s mass bends the space around it so that the Earth moves in a straight line but also circles within the Sun’s curvature in space. The Sun’s affect on time is to slow it down, so time runs slower for those objects close to the massive stellar object. Interestingly, gravity also has an infinite range such that no matter how far apart two masses are in space they will always experience some gravitational pull towards each other. Theoretical physicists have tried to explain this phenomena in terms of gravitons, S-Theory, and M-Theory, but even today a successful quantum theory of gravity has yet to be found.
Time And The Speed Of Light
Speed = Distance ÷ Time
As we now know, the Speed of light (c) is fixed/absolute and represents the inviolable cosmic speed limit. As you travel at relativistic speeds, or those speeds in which the relativistic effect becomes significant, then the distance and time values in the equation become flexible and are forced to change relative to one another. What actually happens is that time and distance are ‘relative’ to one another, and as you travel close to the speed of light, distances become shortened while time is lengthened. This is explained in Einstein’s theory of special relativity.
The following table shows the extent time (one hour) slows down relative to what percentage of the speed of light an object is traveling. As you can see, you don’t need to travel at light speed for time dilation to occur, but you won’t notice the effects until you go extremely fast. Bear in mind, also, that the fastest man-made object ever built, NASA’s Parker Solar Probe, has only managed to achieve a top speed of 430,000 mph (692017.92 km/h or 0.06412% of light speed.
- 0 % of c: 60.00 mins
- 10 % of c: 59.52 mins
- 20 % of c: 58.70 mins
- 30 % of c: 57.20 mins
- 40 % of c: 55.00 mins
- 50 % of c: 52.10 mins
- 60 % of c: 48.10 mins
- 70 % of c: 42.85 mins
- 80 % of c: 36.00 mins
- 90 % of c: 26.18 mins
- 92 % of c: 23.52 mins
- 95 % of c: 18.71 mins
- 99 % of c: 8.53 mins
- 99.9 % of c: 2.78 mins
- 99.997 % of c: 1.17 mins
- 100 % of c: zero mins
Roughly speaking, a person traveling at 99% the speed of light would experience timed slowed by roughly a factor of 7. If they were to travel to a star 7 light years away at 99% speed of light, it would thus take them 1 year to reach their destination, but to an observer on Earth it would have seemed like 7 years have passed. However, if that person attained 99.9999% the speed of light, only 1 year would pass on-board for roughly every 70 years back on Earth. Meanwhile, a speed of 0.9999999 % of c would equate to 2,236 years of time elapsing, a speed of 0.9999999999 of c would see 70,710 years pass on Earth, rising at 0.999999999999999 of c to a staggering 22,369,621 years.
Traveling to the Stars and Time Dilation
As the table above indicates, traveling to the stars at high percentages of the speed of light would allow travelers to cover vast distances but experience very little time. The astronomical distances between the stars subsequently becomes no obstacle at all to traverse and a trip to another star system would feel near instantaneous. The following examples of the time it would take space crews traveling at near-light-speed to reach various destinations will help illustrate this point:
- Alpha Centauri: The near-light-speed craft traveling to Alpha Centauri, our nearest extra solar sun located 4.3 light years away, would take just 4.3 thousandth of a second to complete the journey.
- Milky Way: A space crew would experience 3.2 seconds of time while crossing the 300,000 light years distance to the center of our galaxy.
- Andromeda Galaxy: Located 2.2 million light years away, the journey, as far as the crew are concerned, would last 3.5 minutes.
- Virgo Cluster: Located 40 million light years away, the crew would experience a one and a half hour journey.
- Edge of Universe: An estimated 17 billion light years away, the edge of our universe could be reached within 19 days of crew time.
Timelessness and Immortality
Furthermore, if one day people were actually able to attain light speed travel, then any journey undertaken at said speed would subsequently result in passengers experiencing no time at all. A photon, which is the basic unit that makes up all light, for instance, experiences no time whatsoever between its emission and its absorption. In other words, despite a photon crossing billions of light years of space, the proper time it experiences between any two points on its path is zero and is reduced to just one instant. This idea is encapsulated in an observation made by sci-fi author ray Cummings in his 1919 short story The Girl in the Golden Atom, who noted: “Time . . . is what keeps everything from happening at once”.
Scientists believe photons have zero mass and so cannot decay. Some theories, however, suggest photons might have a minute rest mass and so can eventually decay into lighter elementary particles. According to one study, a photon’s lifetime within its own rest frame amounts to just three years. Nevertheless, photons are still capable of surviving for an estimated billion billion years (1018) because of the time dilatation they experience traveling at the speed of light. Considering the universe is an estimated 13.8 billion years old, it’s fair to say that a photon, for all intents and purposes, lives forever.
7 Mysteries Of Time Explained
1: Did Time Exist Before The Big Bang?
The Universe is believed to be around 13.7 billion years old, before which space and time did not exist and everything was compacted into a singularity smaller than a subatomic particle. According to Einstein’s theory of relativity, it was the Big Bang and its outwards expansion which caused space and time to spring into existence. However, while most scientists currently believe time began with the Big Bang, this is by no means the end of the debate, and quantum physics and an increasing number of new theories continue to pose challenging question about the pre-Big Bang universe.
2: What Is The Shortest Measurement Of Time?
A nanosecond is one billionth of a second, which is a long time compared to a femtosecond (one quadrillionth of a second), or an attosecond (one quintillionth of a second), or yoctosecond (one trillionth of a trillionth of a second) for that matter. According to quantum theory, however, the shortest period of time that can be measured is known as ‘Planck Time‘ (10-43 seconds), beyond which neither time nor space can be divided. Therefore, the closest physics can get to the beginning of time is 10–43 seconds, which represented another way comes to 0.0000000000000000000000000000000000000000001 of a second. During the Planck epoch (0 to 10–43 seconds), the earliest period of the universe’s history, it is believed that the four fundamental forces may have been unified.
3: What Is Space-Time?
“Henceforth space by itself, and time by itself, are doomed to fade away into mere shadows, and only a kind of union of the two will preserve an independent reality”.
Consequently, scientists now view all of physical reality as existing within a single geometric object, known as the Space-Time continuum, with all events described according to their spacetime locations. Minkowski spacetime is often depicted as a two-dimensional lightcone diagram, inside which every object, including people, are located along “worldlines” which are fixed and permanent, the implications of which suggest history is “already there” and exists simply as a timeless object. Supporting this hypothesis is the research conducted by numerous physicists revealing that pairs of particles can communicate with each other across time using their timeline as a quantum bridge.
4: Is Time A Fundamental or Emergent Component Of Reality?
Scientists wonder whether spacetime is a fundamental component of physical reality, like the elementary particles represented in the standard model, and the fundamental forces of nature acting upon them (gravity, electromagnetism, strong and weak nuclear forces), or instead is emergent and holds only a derivative existence. What causes the force between particles, for instance? Is it other particles, the curving of spacetime, or something completely else? At this point, scientists are uncertain, although they do current descriptions of spacetime begins to break down when applied to black holes or the Big Bang, with theoretical physicist Arkani-Hamed suggesting it may in fact be an emergent entity. As he explains:
“Our three-dimensional world is floating in a higher-dimensional space. In fact, maybe the dimensions, and even space itself, are not fundamental concepts. We don’t expect the idea of space to survive in any deeper description of reality. Space almost certainly emerges from something more fundamental. I strongly suspect that even time is an emergent thing.”
A current interesting theory suggests time is actually a side effect of quantum entanglement, with an experimental test on the matter having now been performed by quantum physicists. As online poster pscottdv neatly summed up on “News for Nerds” site Slashdot:
“The point is that time is measured by “events” and “events” occur when the quantum states of two systems become entangled, but only to the systems that became entangled. To an “observer” that has not become entangled, a system is static and no event has occurred. In the Copenhagen interpretation, one would say that according to the entangled observer the “wavefunction has collapsed” whereas according to the unentangled observer, it hasn’t.”
5: How Does Speed Affect Time?
In 1905, Einstein presented his theory of special relativity in which the absolute nature of time, space, and motion was differentiated from its relative properties. He did this after discovering that the speed of light (186,000 miles a second) is constant in all reference frames, a revolutionary concept which presented bizarre possibilities when one considers the formula: Speed = Distance/Time. As one travels closer to the speed of light (c), other parts of the equation start to change with distances become shortened and time becoming stretched. An astronaut traveling at 99% the speed of light, for instance, would experience time roughly 7 times slower relative to an observer, such that if he was traveling at 99% the speed of light to a destination 3.5 light years away he would complete the round trip in 1 year, while on Earth more than 7 years would have elapsed. If he was able to attain a speed of 99.999% the speed of light, however, then that figure would rise to 223 years. One does not need to travel at such high speeds for time to dilate, though, and clocks on-board Global Positioning System (GPS) satellites which travel at speeds of 14,000 km/hr move faster than clock back on earth by around 38 microseconds per day. Uncompensated, this would result in navigational errors of more than than 10 kms each day.
6: How Does Gravity Affect Time?
In 1915, Einstein shook the scientific world when he described space as a dynamic entity distorted by the matter it contains, rather than a static stage on which events unfold. This led to a new understanding of gravity as a curve disturbance in spacetime caused by massive objects, and the acceptance of time as a flexible phenomenon whose rate could to be altered by gravity. Objects near to massive objects, for instance, experience time slower than those further away, and an atomic clock placed in a valley will run slower than one placed on top of a mountain, where the gravitational force would be weaker. In the same way, someone orbiting in a spaceship close to a black hole, but outside of its event horizon, may experience just a few days of time, while for those people further away countless eons may have passed.
7: Could Time Grind To A Halt?
Similar to a wind-up mechanical timepiece giving up its energy, time is slowing down, and may eventually grind to a halt altogether, resulting in all of existence being frozen “like a snapshot” within a single moment in time. That is the radical theory proposed by a team of Spanish scientists headed by Prof Senovilla, and commenting on the claim University of Cambridge cosmologist, Gary Gibbons said:
“We believe that time emerged during the Big Bang, and if time can emerge, it can also disappear – that’s just the reverse effect.”
The new theory questions the established idea of an expanding universe, with ‘dark energy’ then accelerating the process by permeating all of the space available to it. The problem, however, is that dark energy is still a complete mystery to scientists, and the expanding universe theory also seems to contradict gravity and other laws of physics which suggest that since the Big Bang there should have been a gradual deaccelerating expansion as energy levels run lower. According to Prof Senovilla’s theory, the distant galaxies only appear to be accelerating away from each other because deep-space telescopes are looking back to the past when time was going faster, which from our perspective then seems as though they are accelerating.
Black Holes, Relativity And Time Travel
But is time travel really possible? Certainly, as we all travel forward in time by one hour per hour, but can we actually go faster or slower than that rate? Scientists now realize we can after Albert Einstein shook the foundations of physics by demonstrating the flexibile and relative nature of time. An atomic clock placed on top of a mountain, for instance, will experience a weaker gravitational force and so go faster than one placed in a valley, in accordance with Einstein’s theory of General Relativity. Also, as predicted by Special Relativity, an atomic clock on an airplane would run slower that a stationary one back on Earth as time slows down as speed increases.
Time Travel And Special Relativity
Consider the equation Speed = Distance ÷ Time. Einstein‘s theory of special relativity suggests nothing can travel faster than the speed of light, so as the speed of an object approaches the maximum limit set by the speed of light (c), the other variables in the equation start to change with distances becoming shortened relative to time which becomes lengthened.
It actually works out that for a person traveling at 99% the speed of light, time is stretched and slows down by a factor of roughly 7, such that a return journey to a star system 7 light-years away would take the astronaut 2 years to complete, while to an observer on Earth over 14 years would have passed. If, however, our astronaut was able to reach a speed equal to 99.999% the speed of light, then 1 year on board his craft would pass for every 223 years back on Earth.
In addition to speed affecting time, Einstein discovered that gravity, too, causes time to slow down, with the effect more pronounced near a massive object. Therefore, a black hole with its intense gravitational field could potentially provide a fantastic means to travel through time by getting close enough to its Event Horizon without being swallowed up. In principle, by maintaining this “safe” distance you could travel centuries into the future relative to outside observers, although for you just a few hour or days would seem to have elapsed.
Time Travel To The Past
All the scenarios discussed so far involve travelling to the future, but is time travel to the past possible? Yes, in theory at least, as general relativity does allow for a tunnel through space-time linking two distant points in time, which then form a circular time loop called a wormhole or Einsten-Rosen bridge. Similar to a black hole, a wormhole would have a massive gravitational field capable of bending space-time, but in contrast to a black hole’s single point singularity which collapses matter, a wormhole may have a central spinning singularity shaped ring, known as a Kerr black hole. It may then be possible to pass through its “empty” middle through to a white hole on the other side, from which matter is subsequently expelled.
That said, many scientist question the theory of stable, traversable wormholes which are able to be crossed in both directions. Further concerns about time travel to the past are thrown up by temporal paradoxes, such as the Grandfather Paradox, which seem to imply their own negation. Nevertheless, the principles involved in using closed timelike curves to travel and return to ones own spacetime may be perplexing but still remain theoretically possible.
CONCLUSION : We can go into the future. Time travel to the future is possible under Albert Einstein’s general theory of relativity. But time travel to the past is impossible. Because it violates the law of causality, or cause and effect.
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