Time travel may be theoretically possible, but it is beyond our current technological capabilities. (Image credit: argus Shutterstock)
Time travel — moving between different points in time — has been a popular topic for science fiction for decades. Franchises ranging from “Doctor Who” to “Star Trek” to “Back to the Future” have seen humans get in a vehicle of some sort and arrive in the past or future, ready to take on new adventures. Each come with their own time travel theories.
The reality, however, is more muddled. Not all scientists believe that time travel is possible. Some even say that an attempt would be fatal to any human who chooses to undertake it.
What is time? While most people think of time as a constant, physicist Albert Einstein showed that time is an illusion; it is relative — it can vary for different observers depending on your speed through space. To Einstein, time is the “fourth dimension.
” Space is described as a three-dimensional arena, which provides a traveler with coordinates — such as length, width and height —showing location. Time provides another coordinate — direction — although conventionally, it only moves forward.
(Conversely, a new theory asserts that time is “real.”)
Most physicists think time is a subjective illusion, but what if time is real? (Image credit: Shutterstock/Kim D. French)
Einstein's theory of special relativity says that time slows down or speeds up depending on how fast you move relative to something else. Approaching the speed of light, a person inside a spaceship would age much slower than his twin at home. Also, under Einstein's theory of general relativity, gravity can bend time.
Picture a four-dimensional fabric called space-time. When anything that has mass sits on that piece of fabric, it causes a dimple or a bending of space-time. The bending of space-time causes objects to move on a curved path and that curvature of space is what we know as gravity.
Both the general and special relativity theories have been proven with GPS satellite technology that has very accurate timepieces on board. The effects of gravity, as well as the satellites' increased speed above the Earth relative to observers on the ground, make the unadjusted clocks gain 38 microseconds a day. (Engineers make calibrations to account for the difference.)
In a sense, this effect, called time dilation, means astronauts are time travelers, as they return to Earth very, very slightly younger than their identical twins that remain on the planet.
Through the wormhole
General relativity also provides scenarios that could allow travelers to go back in time, according to NASA. The equations, however, might be difficult to physically achieve.
One possibility could be to go faster than light, which travels at 186,282 miles per second (299,792 kilometers per second) in a vacuum. Einstein's equations, though, show that an object at the speed of light would have both infinite mass and a length of 0. This appears to be physically impossible, although some scientists have extended his equations and said it might be done.
A linked possibility, NASA stated, would be to create “wormholes” between points in space-time. While Einstein's equations provide for them, they would collapse very quickly and would only be suitable for very small particles. Also, scientists haven't actually observed these wormholes yet. Also, the technology needed to create a wormhole is far beyond anything we have today.
Alternate time travel theories
- While Einstein's theories appear to make time travel difficult, some groups have proposed alternate solutions to jump back and forth in time.
- Infinite cylinder
- Astronomer Frank Tipler proposed a mechanism (sometimes known as a Tipler Cylinder) where one would take matter that is 10 times the sun's mass, then roll it into very long but very dense cylinder.
String Theory Unifies Space and Time
By Andrew Zimmerman Jones, Daniel Robbins
Einstein’s theory of special relativity has had far-reaching implications, but it has left open certain questions that string theory hopes to answer. It has altered our understanding of time and space. It provides a theoretical framework that tells us how gravity works,
Einstein’s theory of special relativity created a fundamental link between space and time. The universe can be viewed as having three space dimensions — up/down, left/right, forward/backward — and one time dimension. This 4-dimensional space is referred to as the space-time continuum.
If you move fast enough through space, the observations that you make about space and time differ somewhat from the observations that other people, who are moving at different speeds, make.
String theory introduces many more space dimensions, so grasping how the dimensions in relativity work is a crucial starting point to understanding some of the confusing aspects of string theory.
Following the bouncing beam of light
The reason for this space-time link comes from applying the principles of relativity and the speed of light very carefully. The speed of light is the distance light travels divided by the time it takes to travel this path, and (according to Einstein’s second principle) all observers must agree on this speed.
Sometimes, though, different observers disagree on the distance a light beam has traveled, depending on how they’re moving through space. This means that to get the same speed those observers must disagree about the time the light beam travels the given distance.
You can picture this for yourself by understanding the thought experiment depicted in this figure. Imagine that you’re on a spaceship and holding a laser so it shoots a beam of light directly up, striking a mirror you’ve placed on the ceiling. The light beam then comes back down and strikes a detector.
However, the spaceship is traveling at a constant speed of half the speed of light (0.5c, as physicists would write it). According to Einstein, this makes no difference to you — you can’t even tell that you’re moving. However, if astronaut Amber were spying on you, as in the bottom of the figure, it would be a different story.
Amber would see your beam of light travel upward along a diagonal path, strike the mirror, and then travel downward along a diagonal path before striking the detector. In other words, you and Amber would see different paths for the light and, more importantly, those paths aren’t even the same length.
This means that the time the beam takes to go from the laser to the mirror to the detector must also be different for you and Amber so that you both agree on the speed of light.
This phenomenon is known as time dilation, where the time on a ship moving very quickly appears to pass slower than on Earth. In some ways this aspect of relativity can be used to allow time travel. In fact, it allows the only form of time travel that scientists know for sure is physically possible.
As strange as it seems, this example (and many others) demonstrates that in Einstein’s theory of relativity, space and time are intimately linked together. If you apply Lorentz transformation equations, they work out so that the speed of light is perfectly consistent for both observers.
This strange behavior of space and time is only evident when you’re traveling close to the speed of light, so no one had ever observed it before. Experiments carried out since Einstein’s discovery have confirmed that it’s true — time and space are perceived differently, in precisely the way Einstein described, for objects moving near the speed of light.
Building the space-time continuum
Einstein’s work had shown the connection between space and time. In fact, his theory of special relativity allows the universe to be shown as a 4-dimensional model — three space dimensions and one time dimension. In this model, any object’s path through the universe can be described by its worldline through the four dimensions.
One of the elements of this work is the Minkowski (an old professor of Einstein’s) diagram, which shows the path of an object through space-time. It shows an object on a graph, where one axis is space (all three dimensions are treated as one dimension for simplicity) and the other axis is time.
As an object moves through the universe, its sequence of positions represents a line or curve on the graph, depending on how it travels. This path is called the object’s worldline, as shown in the figure. In string theory, the idea of a worldline becomes expanded to include the motion of strings, into objects called worldsheets.
How Warp Speed Works
In order to sidestep the issue of Newton's Third Law of Motion and the impossibility of matter traveling faster than the speed of light, we can look to Einstein and the relationship between space and time. Taken together, space, consisting of three dimensions (up-down, left-right, and forward-backward) and time are all part of what's called the space-time continuum.
It's important to understand Einstein's work on the space-time continuum and how it relates to the Enterprise traveling through space. In his Special Theory of Relativity, Einstein states two postulates:
- The speed of light (about 300,000,000 meters per second) is the same for all observers, whether or not they're moving.
- Anyone moving at a constant speed should observe the same physical laws.
Putting these two ideas together, Einstein realized that space and time are relative — an object in motion actually experiences time at a slower rate than one at rest.
Although this may seem absurd to us, we travel incredibly slow when compared to the speed of light, so we don't notice the hands on our watches ticking slower when we're running or traveling on an airplane.
Scientists have actually proved this phenomenon by sending atomic clocks up with high-speed rocket ships. They returned to Earth slightly behind the clocks on the ground.
What does this mean for the Captain Kirk and his team? The closer an object gets to the speed of light, that object actually experiences time at a significantly slower rate. If the Enterprise were traveling safely at close to the speed of light to the center of our galaxy from Earth, it would take 25,000 years of Earth time. For the crew, however, the trip would probably only take 10 years.
Although that timeframe might be possible for the individuals onboard, we're presented with yet another problem — a Federation attempting to run an intergalactic civilization would run into some problems if it took 50,000 years for a starship to hit the center of our galaxy and come back.
So the Enterprise has to avoid the speed of light in order to keep the passengers onboard in synch with Federation time.
At the same time, it also must reach speeds faster than that of light in order to move around the universe in an efficient manner.
Unfortunately, as Einstein states in his Special Theory of Relativity, nothing is faster than the speed of light. Space travel therefore would be impossible if we're looking at the special relativity.
According to Einstein's General Theory of Relativity, matter bends the fabric of space and time. The distortion of the space-time continuum even affects the behavior of light.
That's why we need to look at Einstein's later theory, the General Theory of Relativity
What Is Space-Time?
The fabric of space-time is a conceptual model combining the three dimensions of space with the fourth dimension of time. According to the best of current physical theories, space-time explains the unusual relativistic effects that arise from traveling near the speed of light as well as the motion of massive objects in the universe.
Who discovered space-time?
The famous physicist Albert Einstein helped develop the idea of space-time as part of his theory of relativity.
Prior to his pioneering work, scientists had two separate theories to explain physical phenomena: Isaac Newton's laws of physics described the motion of massive objects, while James Clerk Maxwell's electromagnetic models explained the properties of light, according to NASA.
Related: Newton's Laws of Motion
But experiments conducted at the end of the 19th century suggested that there was something special about light. Measurements showed that light always traveled at the same speed, no matter what.
And in 1898, the French physicist and mathematician Henri Poincaré speculated that the velocity of light might be an unsurpassable limit.
Around that same time, other researchers were considering the possibility that objects changed in size and mass, depending on their speed.
Einstein pulled all of these ideas together in his 1905 theory of special relativity, which postulated that the speed of light was a constant. For this to be true, space and time had to be combined into a single framework that conspired to keep light's speed the same for all observers.
Einstein's theory of special relativity posited that the speed of light was constant because light always travels at the same speed. (Image credit: Shutterstock)
A person in a superfast rocket will measure time to be moving slower and the lengths of objects to be shorter compared with a person traveling at a much slower speed. That's because space and time are relative — they depend on an observer's speed. But the speed of light is more fundamental than either.
The conclusion that space-time is a single fabric wasn't one that Einstein reached by himself. That idea came from German mathematician Hermann Minkowski, who said in a 1908 colloquium, “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.”
The space-time he described is still known as Minkowski space-time and serves as the backdrop of calculations in both relativity and quantum-field theory. The latter describes the dynamics of subatomic particles as fields, according to astrophysicist and science writer Ethan Siegel.
How space-time works
Nowadays, when people talk about space-time, they often describe it as resembling a sheet of rubber. This, too, comes from Einstein, who realized as he developed his theory of general relativity that the force of gravity was due to curves in the fabric of space-time.
Astronomers witness the dragging of space-time in stellar cosmic dance
Artist's depiction of 'frame-dragging': two spinning stars twisting space and time. Credit: Mark Myers, OzGrav ARC Centre of Excellence.
An international team of astrophysicists led by Australian Professor Matthew Bailes, from the ARC Centre of Excellence of Gravitational Wave Discovery (OzGrav), has shown exciting new evidence for 'frame-dragging'—how the spinning of a celestial body twists space and time—after tracking the orbit of an exotic stellar pair for almost two decades. The data, which is further evidence for Einstein's theory of General Relativity, is published today the journal Science.
More than a century ago, Albert Einstein published his iconic theory of General Relativity—that the force of gravity arises from the curvature of space and time and that objects, such as the Sun and the Earth, change this geometry.
Advances in instrumentation have led to a flood of recent (Nobel prize-winning) science from phenomena further afield linked to General Relativity.
The discovery of gravitational waves was announced in 2016; the first image of a black hole shadow and stars orbiting the supermassive black hole at the centre of our own galaxy was published just last year.
Almost 20 years ago, a team led by Swinburne University of Technology's Professor Bailes—director of the ARC Centre of Excellence in Gravitational Wave Discovery (OzGrav)—started observing two stars rotating around each other at astonishing speeds with the CSIRO Parkes 64-metre radio telescope.
One is a white dwarf, the size of the Earth but 300,000 times its density; the other is a neutron star which, while only 20 kilometres in diameter, is about 100 billion times the density of the Earth.
The system, which was discovered at Parkes, is a relativistic-wonder system that goes by the name “PSR J1141-6545.”
Before the star blew up (becoming a neutron star), a million or so years ago, it began to swell up discarding its outer core which fell onto the white dwarf nearby. This falling debris made the white dwarf spin faster and faster, until its day was only measured in terms of minutes.
Does (general relativity) space-time continuum exist or not without a matter (are there accurate experiments to measure the continuum itself)?
Federal Public Service of Belgium
Federal Public Service of Belgium
University of Oulu
Technologie DMI, Montréal , Canada
Federal Public Service of Belgium
Federal Public Service of Belgium
Technologie DMI, Montréal , Canada
Technologie DMI, Montréal , Canada
- S. V. Kopylov
In the work is shown, that in space-time of dimension (2m) + 1 massless objects do not break parity, and massive, which could it break, do not exist, as well as the corresponding interaction. At the same time, in space-time of dimension (2m+1) + 1 massless objects breaking parity can exist, as well as the corresponding interaction.
Controlling the Space-Time Continuum, With Art
Spacetime Industries is in the business of time management. In the past, time management has been a euphemism for discipline: Either your employer orders you to work faster or you convince yourself that you should increase your productivity by working harder. In other words, it's psychological manipulation. In contrast, Spacetime Industries manages time itself.
We do so by leveraging physics, specifically Einstein's theory of relativity, which treats spacetime as a unified phenomenon. Einstein discovered that time is relative. For instance, time moves more slowly in the gravitational well of a massive object than in the vacuum of space.
Spacetime Industries transforms Einstein's abstruse insights into practical technologies, useful in business and personal life.
Taking into account the enormous amount of money already spent on time management books and consultancies, the growth potential for Spacetime Industries is vast, and the larger we become, the more people we can help to manage their time more effectively. So we are absolutely open to venture capital and to a future IPO.
More important, we hope that large corporations and governments will be interested in our products, because the more people involved, the more efficient society can be.
The potential for large-scale investment in time management can be seen by looking at our plans for time-managed cities, in which different neighborhoods are zoned to run at different clock rates (using spinning hubs to centripetally induce gravitation).
Time in agricultural districts runs much faster than in residential districts, meaning that crops will grow faster while people live longer to enjoy the fruits of their labors. The more that we cooperate, the more meaningful time management becomes because time takes on meaning through our interactions. At the broadest scale, the objective of Spacetime Industries is to foster relationships, through the mechanism of time, for all civilization.
What is a Time Ingot and how do you recommend using it? For example in a business setting, for optimal effect how close should it be placed?
A time ingot is gravitational ballast for temporal micromanagement. In other words, it's a one-pound lead bar that dilates time, much as time is dilated by a black hole or a neutron star.
While the dilation is considerably less than would be achieved by a black hole or neutron star, since a time ingot is considerably less massive than either, it's far more convenient: light enough to deliver by regular mail and compact enough to fit on your desktop.
I would suggest that you keep it safely stowed in a desk drawer until you're waiting for results. At that stage, you should take it out so that the wait is minimized for you, since time will be moving faster for everyone else.
(For instance, you might take out the ingot after delegating a task to an employee of after placing an investment.
) Of course the time ingot can also be used surreptitiously to slow down the actions of a competitor if it's suitably concealed in his or her office, though I cannot recommend this since it would be unethical.