Contemplicity.com

“This is it.” she whispered to herself as she attached the overhead harness to the receptacle on the seat between her legs. Dinah, a young student, was finally going to experience what she had been studying for so long, a negative energy space-time bubble. She sat up straight, fidgeting with the dog eared pages of her notebook, while anxiously awaiting her ship’s departure from the new America Deep Orbit Space Station. After escaping the Earth’s immediate gravitational pull the ship’s new engine, which Dinah helped design, would begin converting stored matter into pulses of negative energy. These pulses would be distributed along the exterior of the ship, warping space-time, and creating a bubble which would exist outside the affects of normal space. But before any of this could take place, they would have to depart from ADOSS. “What’s taking so long?!” She said out loud, a little louder than she meant to actually. Dinah was beginning to wonder if there was a problem with the new engine.
~ If Dinah should get up and inquire about the delay, turn to the last page of this paper…
~ If I should get on with it already, then please continue reading…

By this point in my paper, you are probably wondering just what this paper is going to be about. Due to our linear perception of time, most people would agree that I caused your confusion by first making you read the above nonsense. I would also like to think that most people would agree this essential past leading to the future system is how the universe works. But what if that isn’t always the case? What if the history of the universe wasn’t history at all, but a nearly infinite number of possible histories? And what if this strange multi-history wasn’t yet written? Could we the observer, participate in determining the final outcome, and even more strangely, could we actively change the past from our positions in the present? I think that through the course of this semester we have laid the ground work for tackling just such a question. And I hope that through the course of this paper, I can help the reader better grasp this interesting possibility.

To start, I think we need a little refresher. Now quick, go back and re-read every assignment we’ve had and get with Brent to see if he’ll let you listen to his recordings of each class; or, you could just read through my review of gravity, acceleration, space and time below. Sound a little grandiose? I promise to keep this fairly simple… for nothing more than my own sake. Now, presented with such a task, where does one start?

In the beginning, there was time (assuming you that you believe there was time before the big bang) and probably some unfamiliar form of space (Veneziano 2004). Working with this model of empty space and the passage of time, I hope to perform a series of experiments which will help the reader better understand how time can change in certain conditions. If you will, picture a person who synchronizes their wristwatch with an atomic clock every New Year’s Day, and assume that this wrist watch is a perfect time keeping device (meaning the watch is as efficient as an atomic clock, and encounters absolutely no malfunctions or hazardous events for the duration of its life). If this person conducts themselves in a manner typical to the normal American lifestyle, (i.e. walks, bikes, drives, flies, etc) then when they return to the atomic clock one year later, the clock and the watch would no longer be synchronized. Presuming such an unlikely wrist watch actually existed and that the stationary atomic clock functioned properly, how could this have happened?

The easiest way to answer this question is by using a photon “light clock” (Greene 1999: 38). A light clock consists of two fixed, parallel mirrors, with a single photon of light bouncing back and forth between them. If stationary, the photon will bounce straight up and down at the same constant speed; however, if the clock were riding shotgun in a speeding car, then the photon would have to cover the distance traveled by the car, as well as the distance between the mirrors, before hitting each mirror. (See Figure 1 below for an easier visual explanation.) With this example, it is easy to understand the connection between acceleration and time. But just how closely are they related?

Figure 1. At rest, the photon wants to move straight up and down. From the perspective of the outside observer however, the photon of the moving clock would travel along a diagonal path.

Pretend we have an object, which you place it in a room alone, and completely at rest. Can an object completely at rest still be moving? While this may sound like a contradiction, there is mounting evidence suggesting that such an object would still be moving through time (Greene 1999: 50). While reading this, even though you, your computer, and the objects around you are stationary (relative to the room you are in), you are all experiencing the “movement” of time. And for you and your belongings, time is moving at the same rate, that is to say you and those objects are aging at the same rate. The rate at which you and the other stationary objects are aging is at the speed of light. It is easier to imagine this if you think of time as an extra related dimension to the normal three dimensions of which most of us always think. Figure 2 below illustrates the moon’s orbit around the Earth over a period of time. This light speed aging is what accounts for our observations of time slowing at accelerated rates of speed. In order for an object to move through any spatial dimension, it must divert energy away from traveling through the time dimension. The exchange of energies between speed and time is so equivalent that if all of an object’s energy for traveling through time were diverted to traveling through space (essentially traveling at the speed of light or 670 million miles per hour), that object would no longer feel the affects of time.

Figure 2. While both the moon’s orbit around Earth and the Earth’s orbit around our sun take place in three dimensional spaces, this reminds us that these orbits take place over a given period of time. The last “flat” image shows a specific instant in time.

Acceleration through space is not the only force capable of altering time. The presence of large celestial bodies like our Sun can have drastic affects on both space and time through the exploitation of gravitational forces (Greene 1999: 69). Gravity’s strength is determined solely by the mass of an object, and the distance separating it from other objects. Newton’s theory of gravity states that if any change in these two factors were to occur, the affects would be felt immediately by all objects within the gravitational field of the first massive object. Say for example’s sake, the sun was to explode. According to Newton, even though it takes about eight minutes for the light from our sun to traverse the 93 million miles of space to get to Earth, the Earth itself would immediately notice a departure from its original orbit. Unfortunately for Newton, this is not true, because nothing can outrun the universal speed limit of 670 million miles per hour. The idea that the Earth would instantaneously feel this change was once at conflict with Einstein’s special theory of relativity. Because of this, Einstein would seek out a new theory of gravity fitting with his theory of special relativity.

Later dubbed the general theory of relativity, Einstein’s new ideas about space and time would revolutionize modern physics… again. The basic idea behind general relativity is that acceleration and gravity are both linked to one another. Either force can be used to mimic the other, or to seemingly cancel the other out. An easy way to understand this concept would be to think about free fall rides at amusement parks. Imagine you were traveling to Arizona’s newest and grandest amusement park, where you were looking forward to an exciting trip on Galileo’s Tower. You eagerly wait as powerful motors lift the cart and its passenger’s high into the sky above Tucson. On the way up, you are being pushed back into your seat by gravity and the extra forces exerted on you by the cart’s acceleration. The long awaited moment comes, and the cart plummets back down to the ground below. While falling, you and the other passengers will be in a state of freefall, where, at least temporarily, you will experience a sensation of weightlessness. This is because as you free fall, you are moving at the same rate as your surroundings (in this case the cart, the seats, and other passengers). In this state, you do have weight and are still being acted upon by the force of gravity; however, you don’t notice it as much because of the acceleration. By finding a concrete connection between acceleration and gravity, Einstein was later able to use his knowledge of accelerated movement to better understand gravity. In time, this understanding would lead Einstein to make another link combining accelerated motion and gravity. That link would be the curvature of space and time.

Through out this paper I have shown that gravitational forces can mimic acceleration, and acceleration can change how time affects an object. Therefore, it should go without question that gravitational forces can also affect time in a similar manner as acceleration. This affect is known as space-time curvature and can be seen in Figure 3 below. The closer to the source of a gravitational disruption you travel, the greater the difference in time will become. This affect is known as time dilation. If we are moving through time at light speed, and in order to move through space some of that energy must be diverted from our movement through time, then a gravitational field requires much more of that energy be diverted to move through the same amount of space. While not exactly how it works, you can imagine this affect through visualizing a rubber band. When not stretched, an ant could crawl along the circumference of the rubber band in a relatively short time. If you were to stretch the rubber band, in the manner that a black hole stretches space, then it would take significantly more time for the ant to travel around the exterior of the rubber band. Sometimes the gravitational forces can become so great, that even light can not move fast enough to escape gravity’s pull. This is best exemplified by the event horizon of a black hole, which is illustrated in Figure 3 by the dark ring around the top of the funnel.

Figure 3. On the left, a cross section of a star’s space-time curvature. On the right, a black hole massively disrupts the fabric of space-time around itself.

I hope by now, that I have sufficiently established the links between gravity, acceleration, space and time; however, I have not completely explained what any of this has to do with the present (as well as the future) being able to change the past. Finally, the history lesson is coming to an end, and we can begin to explore the main focus of this paper. But before we can continue, I have one more topic which I feel we need to review, those pesky super position states.

As explained in class, a particle in a superposition state is actually in all possible states simultaneously, as long as it remains unmeasured. The idea is not that we are simply unaware of its true state, but that the act of measuring the particle, forces said particle to choose a state. As strange as this idea sounds, it was accidentally proven by an Irish physicist named John Bell in 1964 (Kosso 1998: 139). The proof behind this idea lies in an expansion of the EPR experiment, which we discussed in class. In short, if you were to create two particles from the division of a single molecule, then both of these particles would spin in the opposite direction. And if you were to measure the first particle’s spin by one of three axes, then the second particle must have the opposite rotation on the same axis. Quantum mechanics tells us this much; however, it does not concretely prove what would occur if you were to measure the first particle along one axis and the second particle along a different axis. Knowing the spin along one of the three axes does not tell you what the spin along a different axis will be.

At best, quantum mechanics can tell you the probability of spin along any axis, and what that probability tells us is rather surprising. The numbers shows us that the spin orientation for these two particles along the three axes can be different up to one third of the time (Kosso 1998: 149). Just because we have measured the direction of spin along the vertical axis, does not mean that the particle has an exact spin orientation along the right or left axes. John Bell proved that the value of spin for these particles can not be a determinate value before that value is properly measured. And only when this superposition state is taken into account, can we make accurate predictions about these particles and the universe around us.

Now I believe we are in a position to better explore the ideas behind how the human observer could affect the history of the universe. Imagine that the entire history of the universe is in a superposition state. To make sense of this, we need to start at the present and work our way backwards. Currently the universe is in a state of constant expansion, but if you were to reverse time, the universe would, of course, be constantly shrinking. The farther back in time you went, the more crowded the ever shrinking universe would become. Fitting all of these incredibly dense objects (planets, stars, galaxies, etc) into an increasingly smaller space would prove to be quite difficult, and this would cause an exponential increase in the curvature of space and time. As I’ve said before, a star or a black hole can drastically alter the passage of time, but what kind of affect would every star, every black hole, and every other celestial body have on space-time when condensed down to an object significantly smaller than a grain of sand? An object this small, with that much density, is what is known as a singularity. A singularity is a place where gravity becomes so strong that space and time are curved beyond any conditions which we would recognize, and in this state, general relativity would no longer be applicable (Gefter 2006: 28).

So, what set of laws would be relevant to a universe in such a state? On this tiny of a scale, the only real laws which would be of any use to us would be on a quantum level. Again I use an example from class, the double-slit photo experiment. If you recall, this idea uses a filter with two slits cut into it facing a sheet of light responsive paper. When light travels through both slits, the light appears as a short series of light and dark bands on the paper. Even when a series of unmeasured lone photons are fired at the slits, the same pattern of dark and light bands appears on the paper. This is because the traveling photon exists in a state very similar to the superposition state. The photon isn’t taking a single path to the paper, but it is in fact taking every possible path. But here’s the really strange thing, when the same experiment is performed with a photon detector to measure the path of the lone photons, the light and dark bands never appear on the paper. Instead, just a single point on the paper responds to the presence of the photons.

This superposition state is not limited to light, but can be applied to every particle on a quantum level. The very building blocks of the universe, the particles which make up the atoms of our bodies and everything we know, can exist in a state in which they have yet to be determined. And just like that photon of light in the double-slit experiment, the universe isn’t limited to a single path, but can take every possible path through time to its current location in the present. If that is truly the case, then just like when we measure the path of a single photon in the double-slit experiment, we could be affecting the history of the universe as we measure it.

This idea of measurements taken in the present determining the past, may seem to be throwing cause and effect to the wind, but that is nothing more than a matter of perspective. If we were able to stand outside the universe, any one of us would easily be able to see the measurement of a photon affecting its path in the double-slit experiment violates causality. However, none of us are able to exist outside the universe. From within the universe, within its laws and passage of time, no observer can see causality being violated in this manner. Now you may think that we are not taking the past from an infinitely possible state, but merely recording a state of which we were not previously aware. The rebuttal to this notion can be found in Bell’s Proof using the Stern-Gerlach device. In Bell’s Proof, the orientation of the measuring device determines which spin orientations are left in a superposition (Kosso 1998: 147). Figure 4 illustrates this idea by presenting a set of histories in superposition. Depending on the equipment used and its orientation to that which is being measured, the measurements will have very different outcomes.

Figure 4. Like a particle in superposition, the universe could have had a nearly infinite number of histories and geometries. When you make measurement, you are selecting from this landscape a set of histories that share the featured which you measured.

Much like string theory, the multi-history universe proposes an idea that seems like an easy way out to those physicists who still think we can absolutely know everything that was going on in the moments before and after the big bang. In most conditions, science requires that our observations be output from the data collected, and we certainly don’t expect our observation to become the input which creates a situation. This sort of thinking robs us of the chance to verify that a theory matches up with our observations. This is certainly a problem, but not a flaw in the idea of a multi-history universe. Quantum theory has always denied us the ability to know everything about the universe we inhabit, for quantum mechanics does not allow us to predict the exact momentum and position of a particle at any time. Even though the idea may be a little hard to swallow, Stephen Hawking of the University of Cambridge and Thomas Hertog of the European Organization for Nuclear Research think there is absolutely no doubt about this model’s accuracy. “It’s simple: if you can’t know the initial state of the universe, you can’t work forwards from the beginning…” (Gefter 2006: 32). According to Amanda Gefter, Hawking would argue that Heisenberg’s uncertainty principal tells us the universe is indeterministic. In this indeterminate state, both the past and the future would be open to change. Because of this indeterminate openness, Hawking argues that the parallel pocket universes implied by string theory should be done away with and replaced by a string theory landscape inhabited by the set of all possible histories. Hawking believes that all of the pocket universes determined by string theory exist simultaneously in one universe, but in a state of quantum superposition. If this were true, whenever you made a measurement, you would be selecting from these superpositioned histories. Essentially, you the observer, would get to choose your past.

The trouble with this idea is that, we the observers are involved in making the history of the universe, not just from the present forward, but from long before the existence of man and well into the future. If this is actually the case, we would have to reevaluate the way we look at the world. Like a reverse choose-your-own-adventure story book, we are in charge of choosing the past. So, does Dinah’s ship ever successfully create that bubble from the beginning of our story? Something tells me that answer lies down a completely different rabbit hole.

Citations, References, and Recommended Reading

Barrow, John D., and John K. Webb. Inconstant Constants. New York: Scientific American, Jun. 2005.
Davies, Paul. That Mysterious Flow. New York: Scientific American, Sep. 2002.
Gefter, Amanda. Exploring Stephen Hawking’s Flexiverse. Cambridge: New Scientist, Apr. 2006.
Gell-Mann, Murray. The Quark and the Jaguar. New York: Freeman, 1994.
Greene, Brian. The Elegant Universe : Superstrings, Hidden Dimensions, and the Quest for the Ultimate Theory. New York: W. W.
Norton & Company, 1999.
Gribbin, John. Q is for Quantum: Particle Physics from A to Z. London: Weidenfeld & Nicholson, 1999.
Kosso, Peter. Appearance and Reality : An Introduction to the Philosophy of Physics. New York: Oxford University Press, 1998.
Veneziano, Gabriele. The Myth of the Beginning of Time. New York: Scientific American, Apr. 2004.