(Globe of Science and Innovation at CERN. Courtesy of Adam Nieman and Wikipedia.)
Dr. Victor Stenger is a physicist who worked for 30 years with neutrinos until his retirement in 2000. He is also an outspoken New Atheist and a leading critic of Intelligent Design. In a recent Huffington Post article (No cause to dispute Einstein), Dr. Stenger has some very sensible things to say about the latest CERN experiments suggesting that neutrinos can travel faster than the speed of light, and not surprisingly, his verdict on the CERN results is negative: “[I]f I were a wagering man, I would bet the effect will go away because of some systematic error no one has yet been able to think of.” But then he goes on to speculate about what the implications of faster-than-light travel would be, if it were ever observed. And here he goes wrong – twice. In the conclusion of his article, where he takes a swipe at belief in God, he not only gets his philosophical theology wrong (which is pardonable enough, for an atheist with no academic background in philosophy), but he also commits a scientific blunder – which is quite astonishing, coming from such an eminent physicist. Stenger’s “case” against theism thus collapses, because it is based on two egregious errors: first, that faster-than-light travel, if verified, would overthrow the distinction between cause and effect; and second, that it would therefore destroy the notion of God as First Cause. I hope that after reading this article, Dr. Stenger will have the grace to acknowledge his errors, and withdraw his argument.
Why faster-than-light travel doesn’t contradict special relativity
Dr. Stenger’s article is scientifically illuminating, despite its errors. Stenger swiftly disposes of the commonly held myth that the discovery of particles which move faster than light would disprove Einstein’s theory of special relativity:
[S]uperluminal [faster-than-light] motion in no way contradicts Einstein’s theory of special relativity published in 1905. Einstein’s equations fully allow for particles to travel faster than light — provided they never travel slower. Physicists have speculated about such objects for years. They are called tachyons. Many searches have been conducted, with no significant signals until now.
Stenger: faster-than-light travel would make causes and effects interchangeable
So far, so good. But then he goes on to assert that if tachyons exist, then cause and effect are interchangeable, and effects can precede causes:
However, there is a problem with tachyons. They imply that cause and effect are interchangeable. Consider the famous duel between Aaron Burr and Alexander Hamilton on July 11, 1804. An observer moving by at less than the speed of light with respect to the participants would have seen the bullet from Burr’s gun enter Hamilton’s lower abdomen. However, another observer moving faster than light would have seen the bullet emerge from Hamilton’s abdomen and enter Burr’s gun. Did Burr kill Hamilton or did Hamilton kill Burr?
The question at the end of Dr. Stenger’s paragraph is muddled; it should read: did the discharge of the bullet from the chamber of Burr’s pistol cause it to enter Hamilton’s abdomen, or did the discharge of the bullet from Hamilton’s abdomen cause it to enter the chamber of Burr’s pistol? The first thing that should be noted is that this is not a “Did A cause B or did B cause A?” question. It’s a “Did A cause B or did C cause D?” question. The entry of a bullet and the discharge of that bullet are two quite different events, even if they occur at the same time and at the same location. So I would have to question Dr. Stenger’s assertion that faster-than-light travel implies that cause and effect are interchangeable.
Stenger: faster-than-light travel means that effects can precede their causes
But this is a minor quibble. Dr. Stenger goes on to claim that if particles can travel faster than light, then effects can precede their causes:
When you read, “Einstein proved that particles cannot go faster than the speed of light” you have to understand that this was not a consequence of the basic axioms of the theory of special relativity. To prove this he introduced an additional assumption now called the “principle of Einstein causality”: cause must always precede effect. In that case, it then follows that we can’t have superluminal motion…
In modern chemistry and physics today, no distinction is made between cause and effect on the atomic and subatomic scales. Time is completely reversible. A carbon atom and oxygen molecule will combine to give carbon dioxide and energy. You can just as well have energy plus carbon dioxide give a carbon atom and oxygen molecule.
In 1948 Richard Feynman showed that, assuming our conventional direction of time an antielectron (“positron”) going forward in time is indistinguishable from an electron going backward in time. Clearly when you reverse time, cause and effect are reversed. But it doesn’t matter. The phenomena that are observed in submicroscopic chemistry and physics can be described either way…
… So, if confirmed, the reported result from CERN or any future observation of superluminal motion will not lead to the overthrow of Einstein’s theory of relativity. Its significance will be to overthrow the distinction between cause and effect. At the worst, Einstein might be faulted for taking causality a little too seriously. (Bold emphasis mine – VJT.)
A few points need to be made here. First, it is inconsistent of Dr. Stenger to argue that the discovery of faster-than-light travel (superluminal motion) will lead to the overthrow of the distinction between cause and effect, and to argue at the same time that “modern chemistry and physics” have already rendered this distinction redundant. He can’t have it both ways.
Second, it is perfectly true that the fundamental laws of physics are time-reversible at the microscopic level: these laws work perfectly well if we run processes backwards in time. However, as physicist Professor Sean Carroll points out in his online article, The Arrow of Time: Frequently Asked Questions, that’s only half the story. As he puts it: “the macroscopic world we observe is full of irreversible processes. The puzzle is to reconcile microscopic reversibility with macroscopic irreversibility.” How do physicists do that? Dr. Carroll explains:
The observed macroscopic irreversibility is not a consequence of the fundamental laws of physics, it’s a consequence of the particular configuration in which the universe finds itself. In particular, the unusual low-entropy conditions in the very early universe, near the Big Bang. Understanding the arrow of time is a matter of understanding the origin of the universe.
For physicists, then, the distinction between cause and effect is not grounded in the laws of physics; it’s grounded in entropy. So for Dr. Stenger to invoke the time-reversibility of the fundamental laws of physics as grounds for doing away with the macroscopic concepts of cause and effect is a little disingenuous.
Third, the ability of physicists to redescribe particles as anti-particles traveling backwards in time has no significance for the notions of cause and effect, as the Wikipedia article on Retrocausality explains:
Feynman, and earlier Stueckelberg, proposed an interpretation of the positron as an electron moving backward in time,  reinterpreting the negative-energy solutions of the Dirac equation. Electrons moving backward in time would have a positive electric charge. Wheeler invoked this concept to explain the identical properties shared by all electrons, suggesting that “they are all the same electron” with a complex, self-intersecting worldline. Yoichiro Nambu later applied it to all production and annihilation of particle-antiparticle pairs, stating that “the eventual creation and annihilation of pairs that may occur now and then is no creation or annihilation, but only a change of direction of moving particles, from past to future, or from future to past.” The backwards in time point of view is nowadays accepted as completely equivalent to other pictures, but it doesn’t have anything to do with the macroscopic terms “cause” and “effect”, which do not appear in a microscopic physical description. (Bold emphasis mine – VJT.)
So far I haven’t accused Dr. Stenger of making any factual blunders; I’ve merely questioned his reasoning. But now I am going to accuse him of making a scientific blunder.
Would faster-than-light travel destroy the very notion of causality?
Dr. Stenger asserts that any future observation of superluminal motion (faster-than-light travel) would destroy the very notion of causality. In his own words, tachyons “imply that cause and effect are interchangeable” and he later adds:
…any future observation of superluminal motion will not lead to the overthrow of Einstein’s theory of relativity. Its significance will be to overthrow the distinction between cause and effect.
Now, I’m not a scientist, so if I were to assert on my own authority that the foregoing statements by Dr. Stenger are scientifically inaccurate, then readers would be quite right to laugh me out of court. But when a physicist with a creditable publication record contradicts Dr. Stenger’s claim, then it would be foolish not to listen to him. The physicist in question is Dr. Sascha Vongehr, who works at the Department of Physics and Astronomy, University of Southern California. In a very readable and entertaining online article entitled, Faster Than Light Neutrinos Do Not Time Travel To Spoil Your Date (Science 2.0, September 27, 2011), Dr. Vongehr states:
Superluminal velocities do generally not violate relativity, or help you to time-travel, or violate causality as long as there is only a single reference frame relative to which the propagation happens instantaneously. Yes, you read this correctly: even infinite velocity can be accommodated in Einstein’s relativity, and the necessary reference system could perhaps be as simple as a quantum tunnel barrier – no need to invoke exotic cosmology. (Bold emphasis mine – VJT.)
Superluminal velocities do not violate causality? How so? Dr. Vongehr explains his reasoning at considerable length in another online article entitled, Neutrinos CAN Go Faster Than Light Without Violating Relativity (Science 2.0, September 25, 2011):
In modern physics, it is well understood how particles can travel with superluminal velocity without violating special relativity or causality. I will discuss such a mechanism here and the novel experiments it suggest in case the recent neutrino physics observations do hold up to scrutiny.
One possibility is very intuitive: Our three dimensional universe may well be due to a three (or more) dimensional membrane inside a higher dimensional, so called bulk space. This is called “universe on a membrane” or short “membrane universe” (MU). This is a well known scenario in string theory but not restricted to string theory. In the MU scenario, our light velocity c is the maximum velocity of excitations inside the MU membrane, the latter being by the way the very reason for why the MU universe observes Einstein relativity inside of it. That velocity c may be very small compared to the maximum velocity of particles that are not bound to our MU membrane, those that speed freely through the bulk space…
The MU scenario is just one – there is a shock wave scenario that is not so intuitive to laypeople. All such scenarios do not touch the relativity that is valid inside the MU: Relativity theory is not violated! The superluminal velocities here can also not violate causality, although relative to carefully selected reference frames inside the MU, the particles actually go somewhat into those reference systems’ past (however, no excitations ever enter a past light cone!). Causality is here trivially guaranteed by the mere fact of that the MU lives through the more fundamental time of the bulk space-time around it (or in other words: the past ‘simply does not exist anymore’ according to the more fundamental bulk time).
If you do not believe me and like to read literature about these scenarios, there are many sources. References to for example the MU and the fact that superluminal speed does not necessarily violate causality you can find in my up to date discussion of these topics ”Supporting abstract relational space-time as fundamental without doctrinism against emergence”.
So there you have it: faster-than-light travel doesn’t violate causality after all, according to physicist Sascha Vongehr. So much for Dr. Stenger’s claim that such travel would overthrow the very notions of cause and effect.
I haven’t gotten to Dr. Stenger’s philosophical blunder yet. Here it is, in the very last sentence of his essay in Huffpo:
Finally, you might want to ponder what effect the demise of causality would have on the notion of God as the ultimate cause of all there is.
Would faster-than-light travel destroy the very notion of God as Ultimate Cause?
Dr. Stenger is right about one thing: if physics ever manages to destroy the notion of causality, then it’s curtains for theism. Without the notion of God as the ultimate cause, the concept of God becomes redundant. That’s why I took Dr. Stenger’s article very seriously when I came across it, through Professor Jerry Coyne’s blog, Why Evolution Is True – see Vic Stenger on speedy neutrinos – did we cause God? At first glance, Dr. Stenger’s article seemed to suggest a way in which the concept of God could be scientifically falsified. Closer examination revealed, however, that its key assumptions were mistaken.
We’ve already seen that the science underlying Dr. Stenger’s argument is faulty. What about the theology? Dr. Stenger gets a couple of important things wrong here.
First, classical theists, for the most part, believe that God is completely outside time. As such, he doesn’t precede His effects, in any temporal sense. Rather, He precedes them in the sense that He explains their obtaining – i.e. the fact that they’re there. Causal priority, then, need not imply temporal priority. I mention this point because Dr. Stenger’s article attacks the assumption now known as the “principle of Einstein causality”: that a cause must always precede its effect. If we’re talking about temporal priority, then theists have never held to such a principle.
Second, theists regard God as the ultimate cause in two distinct senses: He is the Prime Mover (or ultimate cause of change), and He is the Uncaused Being, who maintains all contingent beings in existence. (God is also the ultimate final cause towards Whom all contingent beings tend, as well as being the supreme formal cause Who exemplifies unlimited perfection in his very nature, but I’ll confine my remarks to efficient causes here, since: (i) these best approximate the modern notion of a “cause” and (ii) if God doesn’t make contingent beings exist and make them change – not necessarily deterministically – then He is powerless to act in the world, and therefore not the sort of Being that religious believers would care to worship.)
Now, as Prime Mover, God could be described as the first in a series of causes – although even this is inaccurate, since classical theists have traditionally held that God also acts concurrently with each cause in the chain. In other words, not like this:
God -> X -> Y -> Z
but like this:
God -> X,
God + X -> Y,
God + Y -> Z.
The notion of God as Prime Mover does seem to be threatened if cause and effect turn out to be interchangeable, even if this is only the case within our universe. For if it is impossible to say whether X causes Y or Y causes X, then which one does God cause to move the other? Is it God -> X -> Y or God -> Y -> X? Two possible answers suggest themselves here: one could deny that God ever uses one thing to move another (which is a bit drastic), or one could say that both God -> X -> Y and God -> Y -> X are true (which seems more reasonable). Still, I have to say that it would vastly complicate the Argument from Motion (Aquinas’ First Way), if cause and effect proved to be interchangeable.
With being, however, the picture is much simpler. As the Necessary Uncaused Cause of being, God is the sole and immediate cause of the existence of contingent beings. He maintains these things in existence simply by willing that they should continue to exist. No other being maintains me in existence but God, and in Him, all creatures have their being. That’s what classical theists believe.
Now, if the concept of a Necessary Being makes sense, then it should be obvious to readers that a contingent Being cannot cause a Necessary Being to exist; it has to be the other way round. Here, then, is one causal relation which is by definition asymmetric, even if cause and effect turn out to be interchangeable in all other causes.
Now, Dr. Stenger is a very intelligent man, and I’m sure he will try to argue that the notion of a Necessary Being makes no sense, as pure necessity cannot explain contingency, and as a Necessary Being cannot change other things without itself changing. Classical theists have known about these objections for the last 900 years or so, and they have a ready reply to both. A Necessary Being alone cannot explain the existence of contingent things, but the free choices of a Necessary Being can do so. These free choices are logically ordered, so there is an order of priority among them, but the priority is not temporal, as the Necessary Being is outside time. Thus God chooses to create and maintain this universe freely, but timelessly. Hence the act of creating and maintaining the world does not change Him.
I have always believed that theists and atheists should strive to understand one another’s arguments, for you cannot hope to convert someone to your pint of view if you do not understand his/her position. Before I go, I’d like to recommend two top-notch philosophical papers for Dr. Stenger to read:
I will conclude with a couple of questions for Dr. Stenger.
1. Arguing is by definition an attempt to cause your opponent to change his/her point of view. If Dr. Stenger really believes that the discovery of faster-than-light travel would demolish the very notion of causality, then he should also agree that it also demolishes the rationale for argumentation. So in the event that faster-than-light travel is verified, will Dr. Stenger agree to stop writing books arguing against Intelligent Design?
2. I presume that Dr. Stenger believes that smoking causes lung disease, and that man-made CO2 emissions are causing global warming. Is he prepared to revise these beliefs in the event that faster-than-light travel is verified? If not, why not?
I am not a physicist, and it is possible that I may have misunderstood the point Dr. Stenger was trying to make about causality in his article. If so, I humbly apologize. But when an acknowledged expert is writing for the general public, he/she has the duty to write clearly. I await further clarification from Dr. Stenger.