The fundamental nature of time has always featured prominently in the discussions of scientists, philosophers, and mathematicians throughout the ages. Let us take a look at seven of the profoundest questions about time, and where our understanding of the concept of time is right now.
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 that 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 questions 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 (the strong nuclear force, the weak nuclear force, the electromagnetic force, and gravity).
3: What Is Space-Time?
Albert Einstein may have published his special theory of relativity in 1905, but it was his former college mathematics teacher Hermann Minkowski who first suggested that space and time could be viewed as components within a single four-dimensional structure known as space-time. As Minkowski famously said at the 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, or if instead time 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 current descriptions of spacetime begin 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 becoming 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 were able to attain a speed of 99.999% the speed of light, however, then that figure would rise to 223 years passed on Earth.
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 clocks back on earth by around 38 microseconds per day. Uncompensated, this would result in navigational errors of more than 10 km 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 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.”
This 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.