Time travel 'theoretically possible,' study says: 'The math checks out'
Marty McFly and Doc Brown may have traveled back in time and slightly altered their futures in the "Back to the Future" series, but a newly published study suggests paradox-free time travel is "theoretically possible."
The research, published in Classical and Quantum Gravity, suggests that if time travel were possible and a person changed events in the past, the future would eventually correct itself so the paradox does not exist.
“The maths checks out – and the results are the stuff of science fiction,” the study's co-author, University of Queensland professor Fabio Costa, said in an interview with the university.
Christopher Lloyd, left, as Dr. Emmett Brown, and Michael J. Fox as Marty McFly in the 1985 film, "Back to the Future." (Universal Pictures Home Entertainment via AP)
TIME TRAVEL IS POSSIBLE – BUT ONLY IF YOU HAVE AN OBJECT WITH INFINITE MASS
“Say you traveled in time, in an attempt to stop COVID-19’s patient zero from being exposed to the virus," Costa continued. “However if you stopped that individual from becoming infected – that would eliminate the motivation for you to go back and stop the pandemic in the first place. This is a paradox – an inconsistency that often leads people to think that time travel cannot occur in our universe. Some physicists say it is possible, but logically it’s hard to accept because that would affect our freedom to make any arbitrary action. It would mean you can time travel, but you cannot do anything that would cause a paradox to occur.”
The paradox, or variation, described in the study is a "grandfather paradox." According to the study's abstract, this would allow the observer to "interact in such a way to prevent their own time travel," also known as killing their grandfather and thus preventing being born.
Although confusing, due in part to Einstein's theory of general relativity, which predicts the existence of closed time-like curves (CTCs), CTCs are possible, which would allow a person to interact with a past version of themselves and not cause harm to them in the future.
“In the coronavirus patient zero example, you might try and stop patient zero from becoming infected, but in doing so you would catch the virus and become patient zero, or someone else would,” University of Queensland student and study lead author Germain Tobar added. “No matter what you did, the salient events would just recalibrate around you."
Tobar continued: "This would mean that – no matter your actions - the pandemic would occur, giving your younger self the motivation to go back and stop it. Try as you might to create a paradox, the events will always adjust themselves, to avoid any inconsistency. The range of mathematical processes we discovered show that time travel with free will is logically possible in our universe without any paradox.”
Time Travel Isn’t Possible…or Is It?
Special relativity teaches us that the three dimensions of space and the solitary dimension of time are woven together like a fabric. It’s impossible to think of them as separate entities, only a singular unified entity — space-time. We can’t think of motion through space without being mindful of motion through time, and vice versa. Left-right, up-down, back-forth and past-future are all on equal footing.
And yet, time does seem a little different. We have complete freedom of movement within space, but we cannot avoid our future. Time seems to have an “arrow,” whereas the spatial dimensions are ambidextrous. Given the unity between time and space, it leads to the obvious question: Is time travel, of any sort, possible? Under any circumstances? At all? [How Time Travel Works in Science Fiction (Infographic)]
Into the Future: Sure
Oddly enough, the answer is yes! We cannot avoid moving into our futures, but we can control the rate that we move through time. This is a consequence of another lesson from relativity: Not all clocks are the same.
The speed at which you move through space determines the speed at which you move through time. In the succinct phrase: Moving clocks run slow.
IF you could build a big enough rocket (don’t ask me how, that’s an engineering problem) to provide a constant acceleration of 1g (9.8 meters per second per second; the same acceleration as provided by the Earth’s gravity at its surface), you could reach the center of the Milky Way galaxy — a healthy 20,000 light-years away — in just a couple decades of your personal time.
You could stop for a few hours, have a picnic near Sagittarius A* (the black hole at the center of the galaxy), and then hop back in to your rocket and come back to Earth.
By the time you return you’ll be eligible for retirement benefits, if the institution providing those benefits is even around, because while you only traveled for a few decades according to the clock on your ship, about 40,000 years would’ve passed on the Earth.
Closing the Loop
Time is relative, but it still flows in the same direction for everyone. To ask if we can go into reverse is the domain of general relativity (GR) — this is the mathematical language we use to not only understand gravity, but the full connection between space-time and motion.
In GR, we ask a slightly more technical question: Is there any arrangement of matter and energy (the stuff that warps space-time) to permit the existence of closed time-like curves, or CTCs? I know this is jargon but it’s a fun phrase to toss around at parties. “Curve” here means a path, “time-like” means you never go faster than the speed of light, and “closed” means it returns to its starting point — in other words, its own past.
So, Oracle of Einstein, are CTCs permitted? Yes! Well….
The Possibilities are Finite
There are about half a dozen known configurations of space-time that allow CTCs, or time travel into the past. For example, Kurt Gödel (of Gödel’s Incompleteness Theorem fame) discovered that if the expansion of the universe was accelerating (which it is) and the universe is also rotating, CTCs would be allowed and we could travel into our past on a whim.
As far as I can tell, Gödel used this solution to point out to Albert Einstein that perhaps GR wasn’t all it was cracked up to be — I mean, come on, shouldn’t any self-respecting theory of the natural world avoid such an obviously absurd solution?
But Gödel’s point was moot — all observations indicate that the universe is not rotating, so that particular solution does not apply to our universe, and time travel into the past is verboten.
Ah! But what if we were to construct an infinitely long massive cylinder and set it spinning on its axis near the speed of light. It would drag on space-time around it, and certain paths around that spinning cylinder would end up in their own past. Good thing there are no infinitely long massive cylinders in the universe, or we might have to worry.
Wait, I’ve got one: If you make a wormhole (a shortcut between two distant locations in space-time) and send one end racing off near the speed of light and bring it back, the normal time-dilation effects would put one end in the “future” of the other, so you could waltz right through the wormhole throat and end up in your past. What’s that? Wormholes require “negative mass” to exist, and negative mass does not exist in the universe? Well, hmm.
Into the Past: Nope
It’s the same story every time (pardon the too-hard-to-resist pun). For every scenario we concoct in general relativity to allow CTCs and time travel into our own past, nature finds a way to confound our plans and rule out the scenario.
What’s going on? General relativity allows — in principle — time travel into the past, but it appears to be ruled out in every case. It seems like something funny is afoot, that there ought to be some fundamental rule to disallow time travel. But there isn’t one. We can’t point to any particle interaction at the subatomic level that clearly prevents the formation of CTCs.
The inevitable progression of time from the past to the future resembles another indomitable law of nature: entropy. That’s the iron law of thermodynamics that states that closed systems go from ordered to disordered. (This law explains why an egg will never just happen to unscramble itself if you leave it alone long enough). Is time linked to entropy? Maybe, but that’s the subject of another article….
This story was originally published on Space.com.
“Time Travel Isn’t Possible … or Is It?” was originally published by NBC Universal Media, LLC on August 31, 2017 by Paul Sutter. Copyright 2017 NBC Universal Media, LLC. All rights reserved.
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Is Time Travel Possible? Only Since 1895
Yoel Fink, who is a professor in the departments of materials science and engineering and electrical engineering and computer science, a Research Laboratory of Electronics principal investigator, and the senior author on the study, says digital fibers expand the possibilities for fabrics to uncover the context of hidden patterns in the human body that could be used for physical performance monitoring, medical inference, and early disease detection.
Or, you might someday store your wedding music in the gown you wore on the big day — more on that later.
Fink and his colleagues describe the features of the digital fiber today in Nature Communications. Until now, electronic fibers have been analog — carrying a continuous electrical signal — rather than digital, where discrete bits of information can be encoded and processed in 0s and 1s.
"This work presents the first realization of a fabric with the ability to store and process data digitally, adding a new information content dimension to textiles and allowing fabrics to be programmed literally," Fink says.
MIT PhD student Gabriel Loke and MIT postdoc Tural Khudiyev are the lead authors on the paper. Other co-authors MIT postdoc Wei Yan; MIT undergraduates Brian Wang, Stephanie Fu, Ioannis Chatziveroglou, Syamantak Payra, Yorai Shaoul, Johnny Fung, and Itamar Chinn; John Joannopoulos, the Francis Wright Davis Chair Professor of Physics and director of the Institute for Soldier Nanotechnologies at MIT; Harrisburg University of Science and Technology master's student Pin-Wen Chou; and Rhode Island School of Design Associate Professor Anna Gitelson-Kahn. The fabric work was facilitated by Professor Anais Missakian, who holds the Pevaroff-Cohn Family Endowed Chair in Textiles at RISD.
Memory and more
The new fiber was created by placing hundreds of square silicon microscale digital chips into a preform that was then used to create a polymer fiber. By precisely controlling the polymer flow, the researchers were able to create a fiber with continuous electrical connection between the chips over a length of tens of meters.
The fiber itself is thin and flexible and can be passed through a needle, sewn into fabrics, and washed at least 10 times without breaking down. According to Loke, "When you put it into a shirt, you can't feel it at all. You wouldn't know it was there."
Making a digital fiber "opens up different areas of opportunities and actually solves some of the problems of functional fibers," he says.
For instance, it offers a way to control individual elements within a fiber, from one point at the fiber's end. "You can think of our fiber as a corridor, and the elements are like rooms, and they each have their own unique digital room numbers," Loke explains. The research team devised a digital addressing method that allows them to "switch on" the functionality of one element without turning on all the elements.
A digital fiber can also store a lot of information in memory. The researchers were able to write, store, and read information on the fiber, including a 767-kilobit full-color short movie file and a 0.48 megabyte music file. The files can be stored for two months without power.
When they were dreaming up "crazy ideas" for the fiber, Loke says, they thought about applications like a wedding gown that would store digital wedding music within the weave of its fabric, or even writing the story of the fiber's creation into its components.
Fink notes that the research at MIT was in close collaboration with the textile department at RISD led by Missakian. Gitelson-Kahn incorporated the digital fibers into a knitted garment sleeve, thus paving the way to creating the first digital garment.
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