Relativity-1: Going backwards in time

Part of the reason that recent reports of the detection of neutrinos traveling faster than the speed of light aroused such excitement is because of claims that such a discovery would overthrow Einstein’s venerable theory of relativity and that if you could send a signal faster than the speed of light, you could go backwards in time. Are these claims true or simply overheated? If true, what exactly was overthrown? And what does it mean to ‘go backwards in time’ anyway?

My initial reaction to the faster-than-light neutrino report was one of skepticism, saying that I would wait and see if the result held up but was not hopeful that it would. I did not give my reasons for this pessimism and reflecting later, I thought I should because understanding what was claimed (and why) serves as a good vehicle to understand the elements of the theory of special relativity as well as how science works., so the next series of posts will deal with these questions. (I was overdue for a series of posts on a single topic anyway.)

Let’s look first at the ‘backwards in time’ claim. There is a simple (but wrong) way of interpreting this and a more subtle (but correct) way.

To see the simple way in which something traveling faster than the speed of light can cause things to appear to go backwards in time, think of a situation in which a man fires a gun at another man but with the bullet traveling faster than the speed of light. Nothing requires the shooting of people to understand this phenomenon but this is the customary example that is used, perhaps because a bullet is the fastest object that most people can think of (although it is still much slower than the speed of light) combined with the fact shooting someone is so dramatic and final that reversing the process seems impossible, kind of like Jesus rising from the dead.

Suppose the shooter is at point A and the person hit is at point B 10 meters away. Suppose you are standing right next to the person at B. If the bullet travels faster than the speed of light, what will you see? Remember that we ‘see’ something only when the light from that event enters our eyes. Since the speed of light (at 299,792 km/s) is beyond anything we are familiar with from our everyday experiences, let’s greatly slow things down by assuming that it travels at (say) 1 m/s and that the bullet travels at (say) 2 m/s.

You will see the gun at A firing 10 seconds after it fires because the light from that instant will take that much time to travel the 10 meters to reach you. But one second after the gun is fired, the bullet will have traveled two meters towards B (and you), and light emitted by the bullet at that point will take only 8 more seconds to reach you. In other words, you will see the bullet at the 2 meter point 9 seconds after the gun is fired, which is one second before you see the gun firing. Similarly you will see the bullet at the 4 meter mark 8 seconds after the gun fires, at the 6 meter mark 7 seconds after the gun fires, at the 8 meter mark 6 seconds after the gun fires, and the bullet entering the person at B 5 seconds after the gun fires. Put it all together and what you see first is the person at B being hit (five seconds after the gun fires) and then in the next five seconds will see the bullet emerging from the victim and traveling back and entering the gun.

This no doubt looks like is going backwards in time. But this example is not what is meant by going backwards in time according to the theory of reelativity. After all, the victim was in fact hit five seconds after the gun was fired so there is no actual reversal of the ordering of the events. What you saw is more like watching a film run backwards, which is not really going backwards in time. This effect is an illusion, an artifice caused by the fact that light takes time to travel and your special location next to the victim. Had you observed the whole sequence of events while standing next to the shooter at A, you would not have noticed anything unusual because you would have seen the gun fire right at the beginning, the bullet at the 2 meter mark after 3 seconds, at the 4 meter mark after 6 seconds, at the 6 meter mark after 9 seconds, at the 8 meter mark after 12 seconds and hitting the person at B after 15 seconds. Everything would have seemed normal.

What this example does illustrate is that specifying the time at which an event occurs by the time noted by an observer is not satisfactory because it depends on where the observer is situated relative to the events. (For example, the bullet was observed at the 2 meter mark at 3 or 9 seconds after the gun was fired depending on where you were standing.) We will also see later that in addition to the location, the state of motion of the observer (if you were observing the events from a moving train, for example) also affects the time at which they see events.

It is in trying to unambiguously pin down exactly when something happens that we arrive at a deeper understanding of Einstein’s theory of relativity and what we really mean by going backwards in time.

Next: The CERN-Gran Sasso experiment

Carl Sagan

I never met Carl Sagan but in addition to being a good scientist, prolific writer, great popularizer and advocate for science, he had the reputation of being a really nice person, which is probably why so many of us mean and nasty new atheists are urged to be more like him.

Neil deGrasse Tyson relates an anecdote that reinforces that last characteristic.

The true character of a person is revealed in the way they treat people who, by the usual standards of society, are of no importance to them whatsoever.

Faster-than-light neutrinos?

I came across this BBC report about some observations at CERN that suggested that neutrinos may be traveling faster than the speed of light. If this is true, it would mean that one of the pillars of modern science, the theory of special relativity, would have to undergo serious scrutiny.

I personally was not too excited by the news and was not even planning to comment on it but it seems to be causing a media sensation and several blog readers sent me clippings from various sources and asked for my opinion, so here it is.

I think that this result is unlikely to hold up and so am not too excited. The reason that I am underwhelmed is that I have been around long enough to recall many previous sightings of tachyons (the technical term for faster-than-light particles) that turned out to be false alarms. They are like Elvis sightings in that there is an initial flurry of excitement that then fades under closer scrutiny. The scientists who reported the recent events are aware of this history and are understandably cautious about making any grandiose claims. They can depend on the media to do that. If other research groups study this is some detail and the results hold up, then there will be cause for excitement. This will likely take a couple of years. Until then, I treat this with considerable skepticism.

So my present attitude is captured in this xkcd cartoon that I saw via Jeff at Have Coffee Will Write.

Sorry to be such a downer but if the history of science teaches us anything it is that the great and enduring theories of physics are never overthrown on the basis of a single experiment.

The scientific basis for justice and altruism-part 4

(An expanded version of a talk given at CWRU’s Share the Vision program, Severance Hall, Friday, August 26, 2011 1:00 pm. This program is to welcome all incoming first year students. My comments centered on the ideas in the common reading book selection Justice: What’s the right thing to do? by Michael Sandel. See part 1, part 2, and part 3.)

In the previous post, I pointed out that experiments with babies suggested that although the theory of evolution supports the idea that the desire for justice and fairness is part of our genetic makeup, it is also limited in that seems to stop with our relatives and immediate community or nation. It is not entirely limited, though. There are many examples in evolution of characteristics that evolved to serve one purpose but then get used for other purposes. Sex is a good example. The pleasure it gives served the purpose of encouraging procreation but now people indulge in it for pleasure alone. Similarly, although the desire for justice my have evolved within the domain of kin and the immediate community to benefit the propagation of genes, it can still drive our relationships with the broader community even when there is no genetic benefit.
[Read more…]

The scientific basis for justice and altruism-part 3

(An expanded version of a talk given at CWRU’s Share the Vision program, Severance Hall, Friday, August 26, 2011 1:00 pm. This program is to welcome all incoming first year students. My comments centered on the ideas in the common reading book selection Justice: What’s the right thing to do? by Michael Sandel. See part 1 and part 2.)

There is considerable evidence that the desire for justice and fairness is innate in us. In an article titled The Moral Life of Babies (New York Times, May 5, 2010) child development psychologist Paul Bloom describes how very young children have a strong sense of justice.

A growing body of evidence, though, suggests that humans do have a rudimentary moral sense from the very start of life. With the help of well-designed experiments, you can see glimmers of moral thought, moral judgment and moral feeling even in the first year of life. Some sense of good and evil seems to be bred in the bone.

He reports on experiments in which babies were presented with puppets who either helped or hindered other puppets.

In the end, we found that 6- and 10-month-old infants overwhelmingly preferred the helpful individual to the hindering individual. This wasn’t a subtle statistical trend; just about all the babies reached for the good guy.
…
We found that, given a choice, infants prefer a helpful character to a neutral one; and prefer a neutral character to one who hinders. This finding indicates that both inclinations are at work — babies are drawn to the nice guy and repelled by the mean guy. Again, these results were not subtle; babies almost always showed this pattern of response.

Sometimes the babies were quite emphatic about their preferences.

Not long ago, a team of researchers watched a 1-year-old boy take justice into his own hands. The boy had just seen a puppet show in which one puppet played with a ball while interacting with two other puppets. The center puppet would slide the ball to the puppet on the right, who would pass it back. And the center puppet would slide the ball to the puppet on the left . . . who would run away with it. Then the two puppets on the ends were brought down from the stage and set before the toddler. Each was placed next to a pile of treats. At this point, the toddler was asked to take a treat away from one puppet. Like most children in this situation, the boy took it from the pile of the “naughty” one. But this punishment wasn’t enough — he then leaned over and smacked the puppet in the head.

The toddlers also watched pairs of puppets in which one puppet did a good or bad thing and the other puppet rewarded or punished the first. Of the four possible combinations of actions and consequences, toddlers overwhelmingly preferred the puppets that rewarded good acts and punished bad acts over puppets that rewarded bad acts and punished good acts. This showed that the babies were not basing their preferences on what they perceived as good or bad actions but viewed the actions in the context of the purpose they served. This is pretty sophisticated thinking about crime and punishment and justice.

The desire for justice is strong and biological but is limited. For example, toddlers tend to prefer people of their own races, who speak their own language and share their taste in food. Bloom writes that:

3-month-olds prefer the faces of the race that is most familiar to them to those of other races; 11-month-olds prefer individuals who share their own taste in food and expect these individuals to be nicer than those with different tastes; 12-month-olds prefer to learn from someone who speaks their own language over someone who speaks a foreign language. And studies with young children have found that once they are segregated into different groups — even under the most arbitrary of schemes, like wearing different colored T-shirts — they eagerly favor their own groups in their attitudes and their actions.

So are babies and little children racists? If you waggle your finger and go “kitchy-coo” at a baby of a different racial group, will it bite you? It might, but the babies are not making conscious decisions to prefer their own, which is the real mark of racism. They are simply reacting instinctively based on their biology. So biology seems to strongly suggest that our desire for justice, though it is biologically based on our long history of evolution, is also limited to our in-group. This difference in the way we treat in-group members versus the way we view those who are ‘out-group’ members can and does lead to all manner of strife and tribal behavior between communities, religions, castes, and nations.

So does the theory of evolution say that our biological desire for justice stops with our relatives and immediate community or nation? In the next and final post in this series, I will look at how we overcome that kind of parochialism.

The biological basis for justice and altruism-part 2

(An expanded version of a talk given at CWRU’s Share the Vision program, Severance Hall, Friday, August 26, 2011 1:00 pm. This program is to welcome all incoming first year students. My comments centered on the ideas in the common reading book selection Justice: What’s the right thing to do? by Michael Sandel. See part 1 here.)

The primatologist Frans de Waal in his excellent book The Age of Empathy (2009) provides case study after case study of animals displaying a keen sense of justice and fairness, providing convincing evidence that these impulses are innate in us and arise from our common evolutionary history with other animals. In a newspaper article titled Morals Without God? he writes about his observations:

Chimpanzees and bonobos will voluntarily open a door to offer a companion access to food, even if they lose part of it in the process. And capuchin monkeys are prepared to seek rewards for others, such as when we place two of them side by side, while one of them barters with us with differently colored tokens. One token is “selfish,” and the other “prosocial.” If the bartering monkey selects the selfish token, it receives a small piece of apple for returning it, but its partner gets nothing. The prosocial token, on the other hand, rewards both monkeys. Most monkeys develop an overwhelming preference for the prosocial token, which preference is not due to fear of repercussions, because dominant monkeys (who have least to fear) are the most generous.
…
It is not only humans who are capable of genuine altruism; other animals are, too. I see it every day. An old female, Peony, spends her days outdoors with other chimpanzees at the Yerkes Primate Center’s Field Station. On bad days, when her arthritis is flaring up, she has trouble walking and climbing, but other females help her out. For example, Peony is huffing and puffing to get up into the climbing frame in which several apes have gathered for a grooming session. An unrelated younger female moves behind her, placing both hands on her ample behind and pushes her up with quite a bit of effort, until Peony has joined the rest.

We have also seen Peony getting up and slowly move towards the water spigot, which is at quite a distance. Younger females sometimes run ahead of her, take in some water, then return to Peony and give it to her. At first, we had no idea what was going on, since all we saw was one female placing her mouth close to Peony’s, but after a while the pattern became clear: Peony would open her mouth wide, and the younger female would spit a jet of water into it.

Such observations fit the emerging field of animal empathy, which deals not only with primates, but also with canines, elephants, even rodents. A typical example is how chimpanzees console distressed parties, hugging and kissing them, which behavior is so predictable that scientists have analyzed thousands of cases. Mammals are sensitive to each other’s emotions, and react to others in need.
…
A few years ago Sarah Brosnan and I demonstrated that primates will happily perform a task for cucumber slices until they see others getting grapes, which taste so much better. The cucumber-eaters become agitated, throw down their measly veggies and go on strike. A perfectly fine food has become unpalatable as a result of seeing a companion with something better.

We called it inequity aversion, a topic since investigated in other animals, including dogs. A dog will repeatedly perform a trick without rewards, but refuse as soon as another dog gets pieces of sausage for the same trick. Recently, Sarah reported an unexpected twist to the inequity issue, however. While testing pairs of chimps, she found that also the one who gets the better deal occasionally refuses. It is as if they are satisfied only if both get the same. We seem to be getting close to a sense of fairness.

Can we assume that the human species has also inherited this biological predisposition to justice? Yes, because we are all linked by the great tree of life to all other species. If we go back far enough in our lineages, we will find a common ancestor for all of use, which makes us all effectively cousins, and so you can treat this occasion, where all of us have gathered together in this magnificent concert hall, as a family reunion where you are meeting long-lost relatives. In fact, if you and your pet dog or cat trace your lineages back about a hundred million years, you will find that you have a common ancestor, which is a nice thing to realize.

So given that the desire for justice is so widespread among so many different species, it is very likely that we have inherited the desire for justice from deep evolutionary times. In his book, de Waal concludes that studies in the fields of anthropology, psychology, biology, and neuroscience reveal that we are essentially group animals: “highly cooperative, sensitive to injustice, sometimes warmongering, but mostly peace-loving. A society that ignores these tendencies cannot be optimal.” (p. 5)

But is there any direct evidence that humans have a biological predisposition that makes them favor justice and fairness? Yes there is, and I will explore that in the next (and last) post of this series.

The biological basis for justice and altruism-part 1

(An expanded version of a talk given at CWRU’s Share the Vision program, Severance Hall, Friday, August 26, 2011 1:00 pm. This program is to welcome all incoming first year students. My comments centered on the ideas in the common reading book selection Justice: What’s the right thing to do? by Michael Sandel.)

This year’s common reading book assumes that there is something fundamental about justice that makes its desirability self-evident. What the book discusses are three approaches to justice: the first based on the greatest happiness for the greatest number, the second on respect for the freedom of choice of individuals, and the third on the cultivation of virtue and the common good.

In this talk, I want to examine the very premise that justice is something desirable. What makes us think that people want or seek justice as an end in itself and that the only problem is how to implement that ideal in specific situations? For example, John Rawls’s model of justice (as elucidated in his book The Theory of Justice) assumes that when people are given the opportunity to design a society under the veil of ignorance so that no one knows what situation in life they personally will be placed in, they will create one that is based on the idea of ‘justice as fairness’. Is Rawls justified in assuming that? Is it self-evident that justice is such an obvious good thing that people will want to use it as a central organizing principle?
[Read more…]