The article below, originally appearing in Phys.org*, is one of the best overviews of string theory – clear, concise and precise. While there are dozens of books published on the topic, this article provides the perspective necessary for the continued journey to formulate The Theory of Time.
This is an image of a two-dimensional hypersurface of the quintic Calabi-Yau three-fold. Credit: Jbourjai/Wikipedia.
“(Phys.org) —Scientists at Towson University in Towson, Maryland, have identified a practical, yet overlooked, test of string theory based on the motions of planets, moons and asteroids, reminiscent of Galileo’s famed test of gravity by dropping balls from the Tower of Pisa.
String theory is infamous as an eloquent theoretical framework to understand all forces in the universe —- a so-called “theory of everything” —- that can’t be tested with current instrumentation because the energy level and size scale to see the effects of string theory are too extreme.
Yet inspired by Galileo Galilei and Isaac Newton, Towson University scientists say that precise measurements of the positions of solar-system bodies could reveal very slight discrepancies in what is predicted by the theory of general relativity and the equivalence principle, or establish new upper limits for measuring the effects of string theory.
String theory hopes to provide a bridge between two well-tested yet incompatible theories that describe all known physics: Einstein’s general relativity, our reigning theory of gravity; and the standard model of particle physics, or quantum field theory, which explains all the forces other than gravity.
String theory posits that all matter and energy in the universe is composed of one-dimensional strings. These strings are thought to be a quintillion times smaller than the already infinitesimal hydrogen atom and thus too minute to detect indirectly. Similarly, finding signs of strings in a particle accelerator would require millions of times more energy than what has been needed to identify the famous Higgs boson.
“Scientists have joked about how string theory is promising…and always will be promising, for the lack of being able to test it,” said Dr. James Overduin of the Department of Physics, Astronomy and Geosciences at Towson University, first author on the paper. “What we have identified is a straightforward method to detect cracks in general relativity that could be explained by string theory, with almost no strings attached.”
Overduin and his group —- including Towson University undergraduate research students Jack Mitcham and Zoey Warecki —- expanded on a concept proposed by Galileo and Newton to explain gravity.
Fable has it that Galileo dropped two balls of different weights from the Tower of Pisa to demonstrate how they would hit the ground at the same time. Years later Newton realized that the same experiment is being performed by Mother Nature all the time in space, where the moons and planets of the solar system fall continuously toward each other as they orbit around their common centers of mass. Newton used telescope observations to conclude that Jupiter and its Galilean moons fall with the same acceleration toward the Sun.
The same test could be used for string theory, Overduin said. The gravitational field couples to all forms of matter and energy with precisely the same strength, an observation that led Einstein to his theory of general relativity and is now enshrined in physics as the equivalence principle. String theory predicts violations of the equivalence principle because it involves new fields which couple differently to objects of different composition, causing them to accelerate differently, even in the same gravitational field.
Building on work done by Kenneth Nordtvedt and others beginning in the 1970s, Overduin and his collaborators consider three possible signatures of equivalence principle violation in the solar system: departures from Kepler’s Third Law of planetary motion; drift of the stable Lagrange points; and orbital polarization (also known as the Nordtvedt effect), whereby the distance between two bodies like the Earth and Moon oscillates due to differences in acceleration toward a third body like the Sun.
To date, there is no evidence for any of these effects. Indeed, the standard astronomical ephemeris assumes the validity of Kepler’s Third Law in deriving such fundamental quantities as the length of the Astronomical Unit. But all observations in science involve some degree of experimental uncertainty. The approach of Overduin’s team is to use these experimental uncertainties themselves to obtain upper limits on possible violations of the equivalence principle by the planets, moons and Trojan asteroids in the solar system.
“The Saturnian satellites Tethys and Dione make a particularly fascinating test case,” said Warecki, who is presenting this work at Session 109 at the AAS meeting today. “Tethys is made almost entirely of ice, while Dione possesses a significantly rocky core. And both have Trojan companions.”
“The limits obtained in this way are not as sensitive as those from dedicated torsion-balance or laser-ranging tests,” said Mitcham. “But they are uniquely valuable as potential tests of string theory nonetheless because they cover a much wider range of test-body materials.”
Moreover, in an era of increasingly big-budget science, they come at comparatively little cost, said Overduin.
The Towson-based team presents its finding today, January 6, 2014, between 10 a.m. and 11:30 a.m., at the 223rd meeting of the American Astronomical Society, in Washington, D.C. The work also appears in the journal Classical and Quantum Gravity”
THE THEORY OF TIME IS DEPENDENT ON A QUANTUM MECHANICS THEORY OF GRAVITY
Many theoretical physicists belief that a complete theory of time is contingent upon finding a quantum definition of gravity, which will lead to the Theory of Everything, the Final Theory, the Universal Theory: the reputed theory of theoretical physics that fully explains and links together all known physical phenomena. The primary problem in producing a Theory of Everything is that general relativity and quantum mechanics are hard to unify – the theory of gravity works in the macro (the world we see around us), but does not hold true in the micro world of quantum mechanics. This is one of the greatest unsolved problems in physics today and the solution depends on a greater understanding of gravity.
Accordingly, our search for the theory of time is inextricably linked with two other central questions facing physics today:
Grand Unified Theory, (GUT) and
Theory of Everything (ToE) or Final Theory
Defining the GUT will lead to the ToE, which will provide a foundation for The Theory of Time.
A Grand Unified Theory (GUT) merges three of the four fundamental forces of nature – the electromagnetic and the weak and strong nuclear forces.
Electromagnetism is pervasive in daily life – we see it and use the forces constantly. Additionally, the earth itself produces electromagnetic fields that protects life itself from the harmful rays from the sun.
The weak nuclear force is responsible for radioactivity and decay. The weak interaction finds practical application in the radioactive elements used in medicine and technology, which are in general beta-radioactive, and in the beta-decay of a carbon isotope into nitrogen. At “long” distances, approximately the width of a proton, the weak charge looks smaller because of quantum fluctuations in the vacuum.
In particle physics, the strong interaction (also called the strong force, or the strong nuclear force) is one of the fundamental interactions of nature and is the strongest of the four fundamental forces of nature; but it only has a very short range – a length equal to one quadrillionth of a meter. It is the force that holds the nucleus of an atom together.
Combining GUT with gravity, the last of the four forces, will produce the long sought after Theory of Everything (ToE), which is theorized to produce a complete explanation of the forces in the universe. While this sounds simple, the solution has eluded physicists for nearly 100 years since Einstein presented the general theory of relativity in 1915.
Newton’s theory of gravitation accurately predicts the motion of bodies in the macro – the world we see around us (ie.. apples falling from a tree). HOWEVER, general relativity is incompatible with quantum mechanics. Gravity, pursuant to the general theory of relativity by Einstein, is a consequence of the curvature of Space-time, and provides an accurate approximation for gravity in most physical situations. However theories of quantum gravity do not work in the micro world. We currently do not have a theory for gravitation that works in the micro world of quantum mechanics.
So we are stymied inbetween the quest for a unifying principle of gravity that thrives in the macro world of general relativity and simultaneously resolves the inherent “weirdness” of gravity’s role in the microscopic realm of quantum mechanics.
Finally, we arrive back to the central question, the pebble in my shoe: how can we find a path that will lead us to the Theory of Time.
If I were Newton and could create calculus, we might use math to define the Theory of Time. Such as: Input produces output I
If I were Einstein and could postulate the workings of the universe as a thought experiment, we might use relativity – general or special – to define the Theory of Time using “light cones” (see below – we will utilize the concept later)
However, if I had the intellect of Newton or Einstein, I would have resolved The Theory of Time before my sixteenth birthday and there would be no need for this blog. Being a man whose curiosity greatly exceeds his intellect; we will continue to toil among these big questions with few answers.
Just so life does not get too easy or boring, try to wrap your noggin around the holographic principle of the universe. [Ok, concentrate and read this passage until your brain hurts]
The theory suggests that the entire universe can be seen as a two-dimensional informational structure “painted” on the cosmological horizon, such that the three dimensions we observe are an effective description. So, think of the universe and your reality as a balloon, where you live on the inside of the balloon interacting with reality as a 3D holographic projection of a two dimensional set of “instructions” that is “painted” on the inside walls of the balloon. Stated differently…holy crap – who thinks this stuff up?
Well, actually some of our most respected theoretical physicists. First proposed by Gerard ‘t Hooft, “. . . it was given a precise string-theory interpretation by Leonard Susskind who combined his ideas with previous ones of ‘t Hooft and Charles Thorn. As pointed out by Raphael Bousso, Thorn observed in 1978 that string theory admits a lower dimensional description in which gravity emerges from it in what would now be called a holographic way.” (I hate citing Wikipedia, but you can lookup the specifics and cites).
Note: Please See
[The Holographic Universe, by Michael Tabot, 1992 and 2011]
[Black Holes, Information and the String Theory Revolution – The Holographic Universe, By Leonard Susskind and James Lindsey, 2005 – 2010]
And, of course
[From Eternity to Here – The Quest For The Ultimate Theory of Time, By Sean Carroll, 2010]
Now that we have cleared that up, the question is, what impact does the holographic principle have on a workable theory of time? Importantly, the holographic principle actually solves the black hole information paradox within string theory and independently proves entropy’s role in determining the direction of time (from the past to the future – see previous posts on entropy).
The arrow of time moves from low entropy (order) to high entropy (disorder), pursuant to the 2nd law of thermodynamics. A good example of entropy in action is how the 1000+ pages of War & Peace react to being thrown in the air. If the book is unbound and in single sheets, entropy predicts, correctly, that if the pages are thrown off the 4th floor of a building, they will land in any one of a trillion or more different and distinct combinations – and none of them will have page 1 on top and page 1o00 on the bottom. Just like a broken egg (high entropy-disorder) will never turn back into a whole egg incased in the shell (low entropy-order). This is inspired by black hole thermodynamics.
In the case of a black hole, the insight was that the informational content of all the objects that have fallen into the hole could be entirely contained in surface fluctuations of the event horizon. The holographic principle resolves the black hole information paradox within the framework of string theory.
Now, if you are still confused, take heart – it is said that there are only a handful of theoretical physicists in the world who have the understanding to properly explain the interaction of quantum mechanics, string theory, and the theory of time.
There are a few things in this world that we can always rely on as constants: The sun will always rise each morning, the seasons will always change and time will inevitably march forward at its predictable clip. Except the sun doesn’t actually rise, seasons are disappearing and time … well, see, time is tricky, too.
[[Thanks to M. Yezpitelok and M. Asher Cantrell, this is an great start at looking at some of the issues the confound, confuse and totally invigorate the physics community – enjoy, we will pick up each on to discuss in detail]]
For example …
#7. We May Not Live in the Present
What if we told you that what you think of as “the present” is actually slightly in the past? Basically, your life isn’t a live feed: It’s a delayed broadcast that your brain is constantly editing and censoring for your convenience.
The delay isn’t much — what’s 80 milliseconds between you and your brain? Nothing, right? Well, a group of neuroscientists disagree. They’ve come up with some freaky time-altering experiments to prove that this difference can change your perspective of cause and effect. For example, in one experiment the volunteers were told to press a button that would cause a light to flash, with a short delay. After 10 or so tries, the volunteers were beginning to see the flash immediately after they pressed the button — their brains had gotten used to the delay and decided to edit it out. Yes, that’s a thing your brain can do.
”Being a brain is kind of boring, but we’ve got lots of time for pranks.”
But that’s not the freaky part. When the scientists removed the delay, the volunteers reported seeing the flash before they pressed the button. Their brains, in trying to reconstruct the events, messed up and switched the order. They were seeing the consequence first and the action second.
”You really don’t want to see the copies.”
Not convinced? Try this: Touch your nose and your toe at the same time. Logic says that you should feel your nose first, because it’s right there in your face (hopefully) and therefore the sensory signal doesn’t have to travel too long before reaching the brain, whereas your toe is at the extreme opposite end. The physical distance a message has to travel on neurological pathways is much longer from toes than from nose, and yet you feel both things at the same time. According to neuroscientist David Eagleman, that’s because your brain always tries to synchronize the sensory information that it gets from your body in a way that will make sense to you, but it can only do that by pushing your consciousness slightly into the past, like a radio station that’s always on a five-second delay in case somebody curses on air.
The shortened reflex time gives them an enormous advantage at bull fighting.
But we’re only talking about our perception of time here. It’s not like time itself can actually slow down or speed up in reality … right?
#6. The Higher You Live, the Faster You Age
If you want to experience a real time warp, simply walk up some stairs. It turns out that time isn’t the same all over — it actually runs faster in higher places. In a recent experiment, scientists placed two atomic clocks on two tables, then raised one of the tables by 33 centimeters … and found out that the higher clock was running faster than the lower one at a rate of a 90-billionth of a second in 79 years.
”Timmy, you get down from there before you get cataracts!”
These are the most precise clocks ever made, and the only difference between them was their distance from the Earth. That means people who live in higher places age slightly faster than people at the ground level. So for anyone keeping score, that’s giant people 0, dwarfs 2.
This is called time dilation, and it happens because (as Einstein’s theory of relativity predicted) gravity warps time as well as space. The closer you are to the ground, the more you are affected by the Earth’s gravity and the slower time moves. On the other hand, as you get higher, gravity’s pull weakens and time speeds up.
”Finally! First thing I’m doing is moving away from Colorado.”
Keep in mind that this is an insignificant amount of time we’re talking about here. It has absolutely no bearing on your life — unless you rely on GPS equipment, that is. Because a clock inside a GPS satellite runs at 38 microseconds per day faster than the same clock would run on Earth, a computer has to constantly adjust everything to make up for that difference. Otherwise the consequences would be disastrous: In only one day, the entire system would be off by 10 kilometers, and it would just get worse from then on.
”You have arrived in Calgary. Probably.”
Oh, and by the way, gravity isn’t the only thing that can mess up time …
#5. The Faster You Go, the Slower Time Moves
Another thing GPS satellites have to take into account is speed: The faster you travel, the slower time moves. Now you almost certainly knew that already, thanks to Einstein — if you’re going the speed of light, time pretty much stops. But it turns out that you don’t need an ultra fast spaceship to slow down time — your shitty car will do.
Seriously, man, just let it go. It’s time to move on.
Using the extremely precise atomic clocks we just mentioned, scientists have proven that the same thing happens to you every day, on a much smaller scale. Making one of the clocks move at only 36 kilometers per hour (around 20 mph) caused it to slow down its tick by almost 6 x 10-16. In numbers we can understand, that translates to “Not a whole lot, but still, holy shit, you guys.”
So, let’s say you’re driving to work at around 40 mph — that right there is apparently enough to cause time to move 0.0000000000000002 percent slower than it would if you were standing still.
And, no, that doesn’t explain the actions of the asshole in front of you.
In another experiment, one atomic clock was taken on a plane trip around the world while the other one stayed home (admit it — if you had an atomic clock, you’d constantly be thinking up shit like this). Even though the clocks were perfectly synchronized at first, the traveling clock came back from its 50-hour, 800-kilometer trip missing 230 or so nanoseconds.
And it transformed into a beautiful, majestic moose.
So the clock gained time from being farther from the Earth than the other one, but it lost even more just by going faster. What’s even weirder is that from the perspective of the clock on the plane, the clock back home is the one that’s running faster than normal. You don’t actually feel time slowing down or speeding up: Only someone outside your conditions can tell the difference. And that leads us a little further down this rabbit hole …
#4. Time Doesn’t Run at the Same Speed for Everyone
A trippy consequence of the stuff we just explained is that, apparently, different people can witness the same events happening at different speeds. Einstein claimed that events that appear simultaneous to a person in motion may not look simultaneous to someone who is standing still. So reality may actually be a mess of people walking around in slightly different timelines that sometimes synch up or intersect, depending on their conditions. This would help explain why everyone from Cream looks like a mummy now except for Eric Clapton.
And why he’s dressing as if he thinks it’s still 1978.
Well, according to Meck, this happens because there isn’t a single “clock” that tells the time in our brains: There are multiple brain clocks, all running at different speeds. So basically, the guy in the speeding train, the guy way up in the GPS satellite and the guy at the party working out an exit strategy all coexist inside our heads and our brain decides which one to believe at any given time.
”It’s been six minutes. Man, science is a dick.”
There are lots of other things that can alter our perception of time, like drugs, mental disorders, old age or even distance. With all these variables, time is constantly in flux for everyone. So the next time you’re late for something, just lay that nugget of truth on anyone waiting for you. They may think you’re an asshole, but at least it won’t be for your tardiness.
All we have to do is get them to fly around the Earth really fast so our rotation reverses, and …”
But before you start deciding which dinosaurs you want to see, or which episodes of Dinosaurs you want to see (depending on how lazy you are), keep in mind that we’re not talking about time machines, unfortunately. Scientists say that, at least at first, we’d probably only be able to send short messages back in time and not people or sports almanacs.
Think Twitter instead of Terminator. But even then, neutrinos are invisible and pass right through matter, so it wouldn’t be all that useful for things in the distant past, where they wouldn’t even be noticed. With no way to detect or read the messages, it’d be pointless to send them much further than the recent past. But that brings up an important question of why we’re not getting hundreds of microscopic messages today from our future selves …
#2. Time Stops Outside of a Black Hole
A common misconception with black holes is that they suck up everything around them like a vacuum, but that’s not entirely accurate. What’s really going on is that black holes are so incredibly dense that there is a point of infinite gravity at the center, called a gravitational singularity, and that’s what pulls stuff in — everything from asteroids to light itself. And we’ve already established that gravity and time don’t play well together. So what happens to time when it gets tangled up with a gravitational force so extreme that not even light itself can get free of it?
’80s music gets redefined, that’s what.
It stops. Encircling any given black hole is an area known as the event horizon. It is, for all intents and purposes, the point of no return for a black hole. After the event horizon, the gravitational forces are so powerful that nothing can ever escape.
And because of that insane amount of gravity, an interesting quirk of reality emerges when someone outside an event horizon watches someone inside of one. Imagine your astronaut buddy is David Bowie. Now, say David Bowie calls you (your name is Ground Control for the purposes of this exercise) and tells you he’s floating in the most peculiar way — directly into a black hole.
Don’t worry, the hair will most definitely survive the trip.
If you were watching David Bowie from a safe distance away, you’d see something really weird as he crosses the event horizon: David Bowie’s descent would get slower and slower, and then he’d just stop, and he’d appear to be floating there forever.
From your perspective, it would actually take him an infinite amount of time to fall into the black hole. David Bowie, meanwhile, would notice nothing different, assuming he hadn’t been ripped apart yet. Time would pass normally for him, and he’d still be a snappy dresser to boot.
In fact, if you could somehow exit the event horizon of a black hole after entering it, you’d find that the universe outside had probably aged a significant amount while a much shorter time had passed for you. It’s a foolproof way to travel into the future, except that a black hole can be as small as a tennis ball, and you’d surely be crushed to death.
Shrink rays, Science. Get on it.
Though there’s just as good a chance that we may never have the opportunity to wander through time willy-nilly, because …
#1. One Day, Time Itself Must Die
Time waits for no man, as the old proverb says. It can get all weird under certain circumstances, sure, but that steady beat will keep on going long after we’re dead.
But not too long.
At least not until Bruce Willis and Brad Pitt have a chance to fix it all.
See, the way scientists determine various formulas for how the universe works is via probabilities. The problem is that, if you assume that space-time is infinite, everything — from the mail arriving on time to our sun going supernova and wiping us all out — suddenly has an equal probability on a universal scale.
Since the universe doesn’t work like that and it was fucking with all their formulas, scientists have decided that there must be another answer, and the best they could come up with is that time isn’t infinite.
So it turns out we live in a reality that’s like an old pocket watch, and one day it’s just going to wind down. In fact, when it happens, we won’t even see it coming. The scientists describe it like watching someone falling into the event horizon of a black hole, like we covered earlier. Things slow down and eventually just … stop.
Oh, irony, you are a cruel minx.
The whole of reality will just turn into one big Zach Morris time stop, minus a sassy teenaged guy speaking directly to an implied television audience. We won’t even be aware of what’s happened. Everything will work one second and won’t the next. We’ll all just be frozen in place, completely still. Forever and ever. If nothing else, this should be good incentive for you to literally shit or get off the pot, because you run the risk of being immortalized like that forever.