Category Archives: Physics

Determinism, Free Will, and Quantum Physics

Wayne,

You are not the only correspondent who asks me physics questions.

Here’s an interesting question from a young friend of mine.

I’m interested in hearing your thoughts on the following thought experiment:

Let me pose to you this entirely fantastical scenario: Let’s say there was a way to make copies of the universe such that, up until a given point in history, every aspect of it is exactly the same–every drop of rain that ever fell, every beam of light from every star in the history of the universe, every human choice ever made. Now let’s say that, starting at any given point in history, we can interject an event–say, a person asking another person a question–such that the event occurs exactly the same way, right down to the subatomic level, in every identical parallel universe. Let’s say the question is, “Choose any number between 1 and 100.”

Would we expect the person to choose the same number in every parallel universe? If they do, is this sufficient proof for determinism? But if they choose different numbers, is this sufficient proof for the existence of free will and/or quantum indeterminacy (and to what extent are free will and quantum indeterminacy related?)

Good questions. Today’s the first day of my classes at U of Tampa, and these are the types of questions I have in mind for my The Big Questions slide that I tell my students they will be learning about.

The answer to your first question, according to our best knowledge and thought, is No. Certain types of events that take place in the microscopic world are literally unpredictable. I say that even the world itself can’t predict the outcome, but that’s not the way other physicists might say it.

Here’s an example of such a microscopic event. You shine a beam of light on a partly reflecting mirror, designed so that half of the light arriving at its surface passes through and half reflects. Suppose you turn this mirror so it is at 45 degrees to the incoming light. Half the light goes through, and half makes a 90 degree turn. You put two light detectors in these two beams. A physicist might use a doodad known as a photomultiplier tube. Now you start reducing the intensity of your incoming light beam, by adding shaded filters, and you turn up the sensitivity of your detectors to compensate. Eventually, the incoming beam will appear as a flow of individual particles of light, photons, that appear as sharp peaks in the detector output. Light, those photons, travels at the “speed of light” of course, which is 1 foot per billionth of a second. Suppose the distance from the light source to the light detectors is 10 feet, so each photon takes 10 nanoseconds to go from the source to one or the other detector. Suppose you turn down the light intensity so that you see those detector peak signals about once every microsecond. (These days, these are easy things to do in a laboratory, and we could probably find some physics teacher doing a YouTube showing this.) I think you can do the math: About once every microsecond, you see that a photon has arrived at one of the detectors, and it must have left the source, 0.01 microseconds or 10 nanoseconds earlier. Thus, nearly all the time, there are no photons in your equipment. Every now and then one zips from the source to a detector. You always get a full photon in one detector or the other. You never get a fraction of a photon in one and the rest of it in the other at the same time. A photon cannot be split.

Let’s say that if the photon went straight through, you write down a 1, and if it bounced you write down a 0. You will end up with something like this: …10011010001001011001110010….

If you keep this up for a while, like for a second, which will give you a million 1s and 0s, (because we said that you have about one photon in a microsecond) you will see that nearly 50% of your numbers are 1s and nearly 50% are zeros. In the number above, there are 12 1s and 14 0s. But you won’t see …101010101010101010… very often even though that counts as a random string. Indeed, the pattern of 1s and 0s from your detectors will pass every known mathematical test for randomness. Physicists would say that photons have only a few properties, such as energy and spin, and these do not determine whether any single photon goes through or reflects. Indeed, nothing about the photon before it meets the mirror determines it. Transmission or reflection for a photon is fundamentally random.

Thus, suppose your “interjected event” were a 1 if the photon goes through and a 0 if it reflects. Half of the time, entirely at random, your person would choose 1 and half the time a 0. With a few more mirrors and detectors, I think you can see that we could easily set up your random choice of integers from 1 to 100.

We could do the same experiment with any quantum, microscopic particle, such as an electron, proton, or neutron, or hydrogen atom. While all that I’ve said is in accord with quantum theory, I’d like you to understand that my colleagues have done these experiments, so I’m reporting to you observed results.

While questioning, thoughtful normal people, non-physicists that is, might find this interesting for a few moments, what they are mainly interested in are your subsequent questions about determinism and free will for ourselves. The operations of our brain are (I assert [for good reasons I claim]) entirely the result of immense numbers of microscopic, quantum events acting in accord with the laws of nature, which physicists believe have certain random, undetermined, aspects. Yet when immense numbers of these quantum events occur there may be little randomness in whether a given neuron will fire or not. Up here, in the large world things behave more normally, shall I say. But quantum randomness may still decide outcomes.

Suppose it were to happen that one neuron secretes in a second 998,034 signaling molecules, neurotransmitters, across a synapse, which causes the next neuron to fire, but repeating the experiment, it secretes 997,843 and the next neuron doesn’t fire. The small fluctuation in secreted neurotransmitters is the result of the microscopic quantum events that are the chemical reactions forming the neurotransmitters or their release from some vacuole. If the downstream neuron fires, you order a ham on rye sandwich, if not, a tuna melt. Everything follows the laws of nature, yet sometimes you order one and not the other. But where is the “you” that makes the choice of your own free will about lunch? The fact that the underlying quantum phenomena are random doesn’t provide room for “you” to make the choice, but it will feel to you as if you did.

The answer to your last question, therefore, is that the world is, in some ways, undetermined, but our choices are illusions.

These matters of nature’s behavior and of human perception, free will and determinism, are important and profound. If our actions are the result of our present state and our surroundings with no “you” involved, then what does it mean to hold a person responsible for a crime? Yet we try to distinguish between the mentally ill, compelled to criminality, and a mentally healthy person who commits a crime. The one not guilty, the other guilty, for the same act. Both acts the result of microscopic quantum events that follow the laws of nature. In theology, many argue that the Lord allows us freely to choose and holds us responsible for our choice.  Yet, I say, the Lord appears to have designed the laws of nature so that it is not “we” who make our choices.

I’ve tried to answer your questions by appealing to our deepest understanding of nature, quantum theory, but precise determinism runs into trouble even if there weren’t the unalterable randomness in microscopic quantum events. This is the realm of chaos theory by which the tiniest imprecisions may lead to radically different outcomes. Although the result of each tiny movement forward in time is predictable, to some precision, the result of many tiny movements is unpredictable. Consider the butterfly effect. On a warm summer’s day, a butterfly flits to the left over a hot parking lot, and a tiny blip of air happens to move upward. If the butterfly had moved to the right, no upward moving blip of air. The first case leads to a thunderstorm, the second not. The laws of fluid mechanics and thermodynamics are well-known and complete, but we cannot predict whether there will be a thunderstorm next Thursday. This is weather forecasts are for 70% chance of rain. You can easily imagine that the outcome of brain activity in apparently identical circumstances, a sequence of neurons firing or not, might well be different due to small quantum fluctuations, smaller scale butterfly flutters. All in accord with the laws of nature, determined by them. Yet “you” were not the agent making the choice of quantum outcomes.

Thus, everything follows the regularities of nature, determinism, but some outcomes are random. These random outcomes, ham on rye or tuna melt, are not the result of human agency, but the bistro customer feels as if she chose one or the other.

Bernard

Leave a comment

Filed under Physics

Why Isn’t the Earth Tidally Locked to the Sun (or the Moon)?

Bernard – Looking out my window at the setting moon just now, and wondering: if the moon is tidally locked to the earth hence we always see only one face of the moon, why is the earth not similarly tidally locked to the sun? -Wayne


Wayne,

A good question, but I should say that we don’t see “exactly” the same face of the Moon. Because of details, the Moon shows us somewhat more than 60% of its face as it moves in its orbit. It wobbles a bit.

The Earth is not yet tidally locked to the Moon, which I know is not your question, yet. But it eventually will be, some billions of years from now. The Sun causes tides on the Earth, but they are about half the size of those of the Moon, so whatever the effects of tides are that lead to locking, the Sun’s will operate more slowly than the Moon’s on the Earth.

Here’s the big picture. I’m going to try to show you the Earth-Moon system to scale. The Earth is about 8,000 miles in diameter. The Moon about 2,000. The distance from the Earth to the Moon is about 240,000 miles, or 30 times the Earth’s diameter.

If the Earth is a circle a quarter inch in diameter, the Moon will be a circle a sixteenth of an inch about 7 ½ inches away.

As the volume of a sphere is proportional to the cube of the radius, the Earth’s volume is about 43 or 64 times larger than the Moon. Shall we say that the Earth’s mass is similarly about 60 or 70 times the Moon’s mass? I could look up more exact numbers, but this will do.

The force holding the two in orbit around each other is proportional to product of the masses and inversely proportional to the square of the distance: Newton’s famous law of Universal Gravitation. Consider for the moment, tides in the solid rock of the Moon. They arise because the nearer side of the Moon is closer by, say, 1000 miles than is the far side. The force on the nearer side is greater than the force on the farther side. While the Moon’s center of mass still follows its orbit, this tidal force pulls the Moon into a slightly elongated shape along the line between the Earth and the Moon, and into a slightly squashed shape perpendicular to that line. This tidal force is proportional to the Earth’s mass, and to the difference between the two sides of the Moon, (which is a derivative), so it turns out to be inversely proportional to the cube of distance between the Earth and Moon, 1/r3.

Suppose the Moon is not yet tidally locked to the Earth. It rotates with a different period than it revolves around the Earth. Depending upon whether the rotation period is shorter or longer than the revolution, the pulled and squashed shape of the Moon will not lie exactly along the line between the Earth and Moon. Perhaps the near side will lead a bit and the far side will lag. The Earth will exert a force on that leading bulge closer to it that tends to pull it back to the Earth-Moon line, but the force on the lagging bulge farther away will tend to pull the lagging bulge away from that line. But, the first force is a tiny amount greater than the second force, so pulling back to the Earth-Moon line wins.

Pulling on the Moon’s rocks, stretching them a bit, and then moving that stretch around as the Moon rotates relative to the Earth, involves a little friction. Mostly the rocks are elastic, which means they return to their shapes when you remove the force, but not 100% elastic. That means some of the rotational energy of the Moon gradually transfers from rotation energy into heat energy in the Moon. If you grab a metal strip and flex it rapidly, you will warm it. Thus, the Moon will gradually slow its rotation.

This will keep up, slowing, until the rotation rate and the revolution rate are about the same. Once the tidal bulge is no longer being pulled around the Moon, the frictional transfer of energy from rotation to heating will slow, and things will stay about the same. We see the same face of the Moon, mostly, and never see most of the far side. All this has to do with the Earth-Moon distance, and to the mass of the Earth.

Consider the reverse case. The Earth-Moon distance, of course, is the same as the Moon-Earth distance, but we guesstimated that the Moon is much less massive than the Earth. I looked it up, and a more correct figure is that the Moon is about 1.2% of the Earth’s mass. Or the Earth is about 80 times more massive than the Moon.

The tidal force pulling the solid Earth into an elongation along the Earth-Moon line and into a squashed shape perpendicular to that line is about 80 times smaller than the tidal force of the Earth on the Moon. The vertical displacement of the solid Earth’s tide is about a foot. Hardly noticeable, but scientists with sensitive instruments detect them.

The Earth has oceans and the tidal accelerations cause much larger displacements in the oceans than they do in the solid Earth. To bulge in one place and sink in another, water must flow from what will be lower to what will be higher. These currents experience frictional forces along the ocean floor, and again there is transfer of energy from rotation to heating.

Because, however, of that factor of 80 in the masses, these tidal forces and frictions are about 1% of the forces and frictions on the Moon. The Earth has more rotational energy too. The upshot is that it will take a long time before the Earth locks to the Moon.

What about your actual question, which was why isn’t the Earth tidally locked to the Sun? Now we know the factors to look at to estimate about the Sun-Earth system, as compared to the Earth-Moon system. The Sun is 93 million miles from the Earth, or about 400 times farther from the Earth than the Moon is from the Earth. We must cube this to get the relative tidal force: (4 X 102)3 = 43 X 106 = 64 million. Oh yes. Don’t forget, inverse too. The Sun’s mass is about 3.3 X 105 times the mass of the Earth. So, the Sun is much more massive than either the Earth or the Moon, but it is much farther away.

That difference between r3 and r2 matters. The gravitational force of the Sun on the Earth is much greater than the force of the Moon on the Earth. After all, the Earth, we say, orbits the Sun. But the tidal force of the Sun on the Earth is about half or a third of the tidal force of the Moon on the Earth. We see these solar tides in the seas, and when the solar and lunar tides happen to line up, the tide range is highest, and when they are crosswise, the tides range is lowest.

The upshot of this, is that it will take much longer for the Earth’s day to become the same as an Earth year, and, indeed, much longer than it will take for an Earth’s day to become the same as a lunar month. No need to buy tickets for the event just yet.

Bernard

Leave a comment

Filed under Physics

Global Warming VII – Carbon Dioxide History

Wayne,

Continuing my series of posts (see Global Warming I, Global Warming II, Global Warming III, and Global Warming IV, Global Warming V, Global Warming VI) about Global Warming I have graphs of carbon dioxide in the atmosphere from the Scripps Institution of Oceanography. I think that these are significant for several reasons and in several contexts.

First, these data support my contention that no citizen should vote for any Republican for any office from school crossing guard and dog catcher and higher. That party must be delivered an unmistakable message from voters that it cannot invent its own reality, and it must stop damaging the world.

Second, these data show powerful evidence, through correlation, if nothing else, that human activity has led to a major and still unending increase in CO2 in the atmosphere. As the knowledge that tells us that water vapor and carbon dioxide and some other gases are major factors determining Earth’s climate and temperature goes back more than 100 years and is not in question even by global warming deniers, those deniers have the serious problem of demonstrating why the major increase in atmospheric CO2 has not caused the observed surface temperature increase of recent decades.

Third, these data show that, as many of those who deny the importance of global warming assert, the climate has always changed and will continue to do so. But those who deny the importance of global warming with this true claim, many politicians among them, neglect to mention that the change in CO2 concentrations that we are experiencing is unprecedented in the past million years, at least, and that it extends far beyond the range of any earlier fluctuations.

Fourth, those who assert that humanity should and can merely adapt to these changes, an adaptation that they claim will not be difficult, neglect to mention that the entire span of human civilized existence, about 10,000 years, has also been a span of stable CO2 and stable climate. Thus, we have no certain ideas as to what will happen to the climate in the future nor any way to predict whether civilization will be able to maintain itself. Although this will not make much difference to me, now that I am an old guy, I am an alarmist because I believe alarm is justified.

Fifth, I apologize to coming generations for the mess my generation and a few earlier ones are leaving for them. We have much to be proud of, but global warming is a horrid blot upon our reputations. Continue reading

Leave a comment

Filed under Climate Change, Environment, Natural Science, Physics

Way to go, Trudeau! Quantum computing and the observable universe

Wayne,

This Slate posting recounts Justin Trudeau’s off-the-cuff description of quantum computing during a press conference. Not just a handsome face, and not just a prime minister! (of Canada) His words:

“Normal computers work, either there’s power going through a wire or not, it’s one or a zero. They’re binary systems. What quantum systems allow for is much more complex information to be encoded into a single bit. A regular computer bit is either a one or zero, on or off; a quantum state could be much more complex than that because as we know things can be both particles and waves at the same time and the uncertainty around quantum states allows us to encode more information into a much smaller computer. That’s what’s exciting about quantum computing…”

Bernard


Following links from the splendid piece on Trudeau, I was very much struck by this article by Dennis Overbye. From it:

“So where is the center of the universe? Right here. Yes, you are the center of the universe.

Continue reading

Leave a comment

Filed under Physics, Science in the News, Software

Global Warming III

Wayne,

My first two posts on Global Warming, I and II, dealt with the First Law of Thermodynamics, otherwise known as the Conservation of Energy, and carbon dioxide, an important greenhouse gas. By carefully accounting for energy flows and balances, I showed how researchers establish that increases in carbon dioxide must produce global warming. While the fundamentals, which is all I’m dealing with, are simple, the details and the magnitudes are complicated and turn on details. This is why there are professionals in the business. The professionals are of the view that, when all the details are considered, humans are warming the climate and the warming will be significant.

In this post, I’m going to show some of the temperature change data, as I showed to my students. Of course, the purpose is not to help them to become climate scientists. The title of the book I use is Physics and Technology for Future Presidents, by UC Berkeley physics Professor Richard Muller. Thus what I have in mind for these climate change blogs is to help future presidents and citizens think about this issue, and about scientific claims in general. Also, to tell some stories. Continue reading

2 Comments

Filed under Climate Change, Natural Science, Physics, Science in the News

Global Warming I

Wayne,

When I presented my sermon to my Physics 125 students at the University of Tampa, we happened to be reading and learning about climate change. It was easy for those classes to find material for my Science in the News section. Pro and con, of course.

On Capitol Hill, both Senator Cruz, Chair of the Senate’s relevant science committee, and Congressman Lamar Hunt, Chair of the House’s committee, have been holding hearings. Both of these guys are Texas Republicans, and it is both astonishing and disgraceful that such men are in their positions of power over American science. Senator Cruz’s hearings mostly had to do with witnesses and Republican Senators denouncing the world-wide conspiracy among climate scientists, environmental alarmists, and left-wingers intending to destroy the American economy and install socialism. Congressman Hunt’s hearings have to do with his suspicions, so he says, that some government scientists have cheated by cooking the books so as to demonstrate that the supposed global warming pause did not exist. Of course, there is no such conspiracy, and the global warming pause did not and does not exist, and the scientists didn’t cook the books.

One thing that’s astonishing about the Republican Party’s denial of the results of years of climate research is that the fundamental aspects of the theory and data are elementary and not in dispute among scientists. What scientific fussing there is within the climate science community has to do with details, and those scientists are in remarkable agreement that the climate is warming and that we are causing it.

As I am testing my new connection from Word to WordPress, I thought I would explain these basics, as I did to my students. These students are not science majors, but are taking a required natural science course. The course is more a great ideas of Western Civilization course than a regular course for physics students. Thus I based my presentation to them upon the First Law of Thermodynamics or the idea of Conservation of Energy. Of course I had to include some facts, observations, and ancillary principles. Continue reading

3 Comments

Filed under Climate Change, Natural Science, Physics, Science in the News

Sermon and Pep Talk for My Physics 125 Students

Wayne,

I’m about 2/3rds of the way through my Physics 125 course at the University of Tampa. This course is one of several natural science classes required of students who are not majoring in science. The other two are an astronomy course and a chemistry course. These students also have to take a biology course.

The text is Physics and Technology for Future Presidents: An Introduction to the Essential Physics Every World Leader Needs to Know, by Univ. of Calif. Physics professor Richard Muller.

The text and the course are nearly devoid of mathematics beyond multiplication and division, and interesting (to me and I hope to the students) applications of the major principles are everywhere. I do a 10 minute or so Science in the News talk each day, and I have had no trouble finding breaking news that is often directly connected to the material the students are studying.

I like the students, and they are working hard, I think, but some of them are stressed out. So I’ve decided to give them a sermon and pep talk tomorrow. Here’s a draft.
Continue reading

2 Comments

Filed under Natural Science, Physics