The very readable cosmologist Ethan Siegel has a long-running "Ask Ethan" series of posts that are sometimes characterized by explanatory overconfidence, in which Ethan often acts as if he understands great mysteries that are actually far beyond the understanding of any human. An example is his latest post in the series in which he incorrectly states that "we know what makes up the Universe — i.e., what our ratios are of dark energy to dark matter to normal matter." No, we don't know any such things, and no one has ever even directly observed dark matter or dark energy, which don't even have any place in the standard model of physics. We don't even know whether dark matter or dark energy exists. I wish I had a nickel for every time a scientist said "we know" about some thing that is not actually known; I'd be rich.
Siegel's latest post in this series is a post raising the question "Why Is the Universe Electrically Neutral?" There is a kind of a half-answer to this question: the universe is electrically neutral because from the very beginning there has been a law of nature (the law of conservation of charge) that guarantees electrical neutrality in any universe beginning in an incredibly hot and dense state such as the Big Bang. But this is only a half-answer, because there is no known intrinsic reason why such a law had to exist from the beginning. Rather than explaining how this law foreordained an electrically neutral universe from the beginning, Siegel refers us to speculative papers he has written that do not give us the main reason the universe is electrically neutral.
When a person refers to the electrical neutrality of the universe, he means the apparent fact that the total amount of positive electric charge in the universe seems to be equal to the total amount of negative electric charge in the universe. At the lowest level, such electric charges are found in protons and electrons.
Below are some of the fundamental constants of the universe, numbers that are believed to be the same everywhere in the universe:
| Speed of light | 299,792,458 meters per second |
| Planck's constant | 6.62607004 × 10-34 m2 kg / s |
| Gravitational constant | 6.67408 × 10-11 m3 kg-1 s-2 |
| Proton mass | 1.6726231 × 10-27 kg |
| Electron mass | 9.1093897 × 10-31 kg |
| Proton charge | 1.60217733 × 10-19 coulomb |
| Electron charge | -1.60217733 × 10-19 coulomb |
The table below shows a a great big coincidence scientists cannot explain. Even though each proton has a mass 1836 times greater than each electron, the charge of the proton is the exact opposite of the charge of the electron. An absolute magnitude is a number that you get when you discard the sign in front of the number. Experiments have actually indicated that the absolute magnitude of the proton charge and the absolute magnitude of the electron charge differ by less than 1 part in 1,000,000,000,000,000.
|
RATIO OF PROTON MASS TO ELECTRON MASS | |
| 1836.152672 | |
| RATIO OF PROTON CHARGE TO ELECTRON CHARGE | |
| -1.000000000000000000 |
A physicist might try to offer an "explanation" for this coincidence by referring to the idea that protons are made of smaller particles called quarks. The theory is that each proton consists of three particles: two "up" quarks with a positive charge of 2/3 of the proton's charge, and one "down" quark with a negative charge of 1/3 of the proton's charge. But this really only worsens the explanatory problem. Under such a scheme we have not just one very precise electric charge coincidence in the fundamental constants of nature, but two such coincidences:
(1) The coincidence that the absolute value of the proton charge has always been very precisely equal to the absolute value of the electron charge;
(2) the coincidence that the absolute value of the up quark has always been very precisely twice the absolute value of the down quark.
Doubling the number of very precise coincidences isn't really anything in the way of explanation. In the informative and entertaining book We Have No Idea by physics professor Daniel Whiteson and Jorge Cham, on page 54 the authors state this:
"If the quarks had any more (or less charge), then the charge of protons wouldn't precisely balance the negative charge of the electron, and you couldn't form stable neutral atoms. Without these perfect -1/3 and + 2/3 charges, we wouldn't be here. There would be no chemistry, no biology and no life."
But is there any explanation for this? Apparently not, because the authors next state this:
"This is actually fascinating (or creepy, depending on your level of paranoia) because, according to our current theory, particles can have any charges whatsoever; the theory works just as well with any charge value, and the fact they balance perfectly is, as far as we know, a huge and lucky coincidence."
Life could have existed if protons and electrons both had some different charge, but only if the proton charge was the exact opposite of the electron charge. The situation is illustrated in the diagram below (when reading the diagram, imagine that the green line is less than a billionth of the width of the square):
As far as we know, our planet has an equal number of protons and electrons, and our planet is electrically neutral, having an equal amount of positive charge and negative charge. Given that electromagnetism is a force very roughly a hundred trillion trillion trillion times stronger than gravity (the force that holds our planet together), it seems that even the tiniest imbalance (such as 1 part in 1,000,000,000,000) between the proton charge and the electron charge would result in an electrical imbalance strong enough to prevent a planet such as ours from holding together.
On page 64 of his book The Symbiotic Universe, astronomer George Greenstein (a professor emeritus at Amherst College) says this about the equality of the proton and electron charges:
"Relatively small things like stones, people, and the like would fly apart if the two charges differed by as little as one part in 100 billion. Large structures like the Earth and the Sun require for their existence a yet more perfect balance of one part in a billion billion."
You can read the quote above in its original context using this link.
In fact, experiments do indicate that the absolute value of the charge of the proton and the electron match to fifteen decimal places, differing by less than one part in a million billion (1 part in 1,000,000,000,000,000).
Scientifically speaking, what kind of explanation can be given for this equality of positive charge and negative charge in the universe? The only thing that can be offered is a kind of half-explanation: a reference to a law of nature. The law is called the law of conservation of charge. According to the law of conservation of charge, any event that causes an increase in electrical charge must also cause a corresponding decrease in electrical charge; and any event that causes a decrease in electrical charge must also cause a corresponding increase in electrical charge.
The best way to illustrate this law is to refer to the high-energy collisions that occur in particle colliders such as the Large Hadron Collider. In that massive machine, particles are accelerated to almost the speed of light. When two very high-energy particles collide at such speeds, they create mainly out of energy new matter particles such as protons and electrons. Following Einstein's famous equaion of E=mc2, energy can be converted to matter, and vice versa. But following the law of conservation of charge, nature always "balances the books" so that the number of protons created equals the number of electrons created. For example, if a high-energy collision creates 1000 new protons mainly from energy, then also exactly 1000 new electrons are created. And if a more energetic high-energy collision creates 8338 protons from energy, then also exactly 8338 electrons are created.
Given such a law of nature, and a universe beginning in an extremely dense and hot state such as the Big Bang, electrical neutrality follows as a consequence. In the earliest moments of the Big Bang, the universe was so hot and dense that everything was like the high-energy collisions occurring in the Large Hadron Collider. With a "balance the books" charge conservation law being followed everywhere, it was inevitable that the result would be an equal amount of positive charge and negative charge. But this is merely a kind of half-explanation. For we do not understand why such a law existed.
Brittanica.com states the law of conservation of charge as the law that "at a subatomic level, charged particles can be created, but always in pairs with equal positive and negative charge so that the total amount of charge always remains constant." It describes this rather intricate "balance the books" system within nature:
"When a charged particle changes into a new particle, the new particle inherits the exact charge of the original. When a charged particle appears where there was none before, it is invariably accompanied by another particle of equal and opposite charge, so that no net change in charge occurs. The annihilation of a charged particle requires the joint annihilation of a particle of equal and opposite charge. "
Brittanica.com mentions mentions three other conservation laws, saying, "The laws of conservation of energy, momentum, and angular momentum are all derived from classical mechanics." But no such claim is made about the law of conservation of charge. There would seem be no contradiction if no such law existed, and we should not expect any such law of the conservation of charge to exist in a random universe.
The term "law of the conservation of charge" is something of a misnomer, because charge itself is not conserved. Over billions of years, stars convert matter into energy, resulting in a gradual decrease in the number of charges in the universe (as fewer protons and electrons exist). What is conserved is the ratio of positive charge to negative charge. The law of the conservation of charge would be better named as the law of the preservation of the ratio of charges. But scientists would not like to use such a more accurate term, which would tend to make the universe sound like some purposeful, programmatic, mathematically-minded bookkeeper interested in the preservation of mathematical ratios.
Imagine if there was a strange law in your household that you called the Law of Money Balance. The law might work like this: whenever you lost money, you would gain an equal amount of money. And whenever you gained money, you would lose an equal amount of money. So, for example, if there was a hole in your pocket and you lost $50 by dropping it on a crowded street, you might come home and find there was $50 that mysteriously appeared on your coffee table. And whenever you saw that there was some direct deposit of $4000 sent by your employer as a salary payment, you would find that there was at the same time some mysterious withdrawal of $4000 from your bank. This would be great if you started out as a millionaire. No matter how much money you spent, you would always end up with the same amount of money, so you would always stay a millionaire.
You might take such a law for granted, regarding it as some "natural law of how reality works." Or if you started out as a millionaire you might reasonably suspect that the strange law was some providential blessing. Ditto for the law of conservation of charge, something we would not expect to exist in any random universe.
In his recent post Ethan Siegel does a poor job of attempting an answer to the question: why is the universe electrically neutral? He fails to explain how the law of conservation of charge is the underlying physical law behind the universe's electrical neutrality (the perfect balance of positive electric charge and negative electric charge). Referring to failed wildly speculative "grand unification theories" never supported by evidence, Siegel speculates wildly about how the universe could have begun with an imbalance of proton charge and electron charge, something that would have been in violation of one of our universe's main laws, the law of conservation of charge. He then refers us to some imaginative paper he wrote that speculates about how such a universe with charge imbalances might have become more electrically neutral. All of that makes up a very bad explanation as to why the universe is electrically neutral. A much better and simpler explanation (although only a half-explanation) is to explain how our universe has always had a law (the law of conservation of charge) that guarantees that there would be a perfect balance of positive and electric charges. But since we have no scientific explanation for why so convenient a law exists, one of many very convenient laws of nature necessary for our existence, this is merely a kind of half-explanation.
We take for granted a law such as the law of the law of conservation of charge, because it is has always existed. It seems that anyone always enjoying the blessings of a favorable law of nature will take that law for granted, no matter how improbable that law would be in a random universe. For example, if we lived in a universe in which people always had nice gentle landings whenever they jumped off of high cliffs or high buildings, we might call such a law "the Law of Gentle Landings," and think that it was nothing special, not any providential blessing. And if we lived in some universe in which nice tasty well-cooked food would always conveniently drop from the sky at dinner time, gently landing in our back yards, we might call that regularity "the Law of Convenient Food Delivery," and think that it was nothing special, not any providential blessing, but just some law of nature to be taken for granted. We would say "there's nothing special" about such a law, and claim that "it's merely the way nature works," language also strangely used about the law of conservation of charge.
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