What about the second example, of someone who was on the road and heard a cry out? Is that too only impossible on the physical level? And if not, then what exactly is the problem with praying about the past?

It’s exactly the same thing. The problem is—and I wrote this in the trilogy as well—that the Holy One, blessed be He, apparently does not really intervene in nature (that is, He does not even do things that are physically impossible. Of course, in principle He can do so, but He decided not to). The Sages thought that prayer about the future is not intervention, while prayer about the past is. Today we understand that changing the future is also intervention in nature, and you can draw your own conclusions.

Rabbi, I’m not sure that if the Sages had known that nature is deterministic they would have given up on prayers altogether. One could simply explain that this kind of intervention that changes the past (even though your wife screamed, she actually didn’t scream) is too drastic, as opposed to a local intervention that affects only the future.

There is the example of “if his wife was pregnant,” that after forty days he should not pray that she give birth to a male,
and here the miracle would not be completely evident,
and even so his prayer is considered a vain prayer.

Any time travel is a logical paradox, because events that did or did not happen in the past are defined as “did happen” or “did not happen,” and by means of this “return” you are assassinating the definition.

And regarding the passage in Berakhot, the responding rabbi apparently did not look inside What God Cannot Do itself, nor at the passage itself, because it is the Mishnah that compares prayer about the fetus to prayer about the past. As for the Rabbi’s claim that prayer about the fetus could also be about the future, that is already dealt with there in What God Cannot Do.

Chal, I disagree. I referred to my book there, where I show that this is not a logical contradiction (and, with a bit more ad hominem: apparently all the physicists who deal with the feasibility of this also think so). Moreover, if this were a logical contradiction, then it would also be impossible to discuss the law of retroactive clarification or a condition taking effect from now, because a logical contradiction is impossible even when we are dealing not with facts but with norms (either she was divorced or she was not. Both together are a logical contradiction).

Beyond that, whatever our view may be about time travel, as I explained above—in the passage about praying over the past, we are not dealing with time travel at all.

Indeed, I had not looked at the book and responded only to what was written here in the question. It may very well be that he discusses this there. But the comparison between prayer about a fetus and prayer about the past was explained by me perfectly well. So I did not understand what your comments have to do with mine. I am arguing that prayer about the past does not necessarily mean time travel. Notice that I am not disputing the term “prayer about the past,” but only explaining it differently.

As for the question of the fetus, whether this is about the past or not, I wrote here what seems right to me. If you want to bring here another explanation or argument that appears there, I’d be very glad. As I said, I haven’t read it.

On the forum “Stop Here Think,” they say they copied this point from the book, and I’m copying what they brought there—there is much more in the book, but I don’t have the energy to copy it myself.

“The Talmud merely argues against the Mishnah, which chose for itself the case of ‘May it be Your will that my wife give birth to a male’ as a classic example of ‘crying out over the past,’ alongside ‘He was coming on the road and heard a cry in the city, and says: May it be Your will that it not be from my household.’ And this, the Talmud claims, is apparently without justification; in the case of ‘a cry in the city,’ only a change in the laws of logic would help solve the problem, whereas in the case of ‘May it be Your will that my wife give birth to a male,’ the issue could also be solved quite simply by changing the laws of physics, by reversing the sex of the fetus from now on, as in the story of Dinah. Why, then, should a person in such a case need specifically a prayer to change the laws of logic, to the point that the Mishnah uses this as an example for the prohibition of such a prayer?! By comparison, the case was not given of a person praying to be healed from his illness in such a way that the illness would disappear retroactively, in order to establish that ‘this is a vain prayer.’ That is because such a depiction is illogical: a person praying to be healed from his illness wants the illness to stop afflicting him from now on, but why would he also want the past changed, since at this point that no longer makes any difference? In the same way, a person who wants his wife to give birth to a male would ask that the sex of the fetus be changed from now on, a change that involves nothing more than violating the laws of physics, so why should he also pray about the past, such that the Mishnah would use this as an example for its law?

“To this the Talmud replies and distinguishes between the cases, that ‘we do not mention miraculous acts.’ That is, philosophically speaking there is certainly an abyss between a miracle involving changing the laws of physics and a miracle involving changing the laws of logic; however, from the standpoint of the ordinary person praying, there is no difference between the cases. For as is usual in everyday life, even miracles that involve only changing the laws of physics are not at all common, so that a person who is already trying through prayer to change the sex of his wife’s fetus is not so precise in his prayer as to distinguish between a retroactive change and a change from now on. From the standpoint of daily experience, both are equally uncommon, and therefore it is legitimate for the Mishnah to take as an example of prayer to change the past, ‘May it be Your will that my wife give birth to a male,’ and not ‘May it be Your will that I recover from my illness retroactively.’ But with regard to Jewish law, indeed so; only a prayer to change the sex of the fetus retroactively is forbidden, whereas a prayer to change it from now on is permitted and entirely legitimate, just as Leah in fact prayed regarding Dinah.

“And in this many later authorities went astray, for because of their ignorance in philosophy they did not grasp the enormous difference between prayer to change the laws of physics and prayer to change the laws of logic, and as a result they did not understand the Mishnah and the Talmudic passage at all…” End of the quotation from the book (note 30, pp. 19–20), and anyone who wants can look there further.

That’s the end of the quote from Stop Here Think; see there:

http://www.bhol.co.il/forums/topic.asp?cat_id=24&topic_id=3134493&forum_id=1364

As for what you brought from the law of retroactive clarification, it doesn’t seem to me that this is connected to the issue of time travel. In that case, it was already determined in the past whether the woman was divorced or not, and what is happening now is only clarification retroactively. Maybe you’ll argue that this leads to a deterministic view, but so what? If it were a moral question, a problem would arise with free choice, but in most of the cases the Talmud brings on this topic there is no moral problem, and even if there were, presumably we could somehow manage.

If you claim to have a solution to the issue of time travel, I’d be glad if you’d write it briefly. Unless it’s Dummett’s solution, which tries to argue even with the Mishnah in tractate Berakhot (!), and is already discussed there in What God Cannot Do.

That quotation didn’t really change anything. What he says about changing the sex of the fetus is exactly what I wrote here. As for hearing a cry in the city, contrary to his assumption, that too is not against the laws of logic (and in general, no change in the world is really against the laws of logic). The Holy One, blessed be He, can change the disaster, such as a fire, from now on (heal those who were burned and burn others in their place).

A consistent definition of time travel requires two time axes, with the return taking place only on one of them. The basis of this is found in McTaggart, and I develop it further in the fourth book of Talmudic Logic.

As for retroactive clarification, we are speaking of human actions that plainly depend on free choice (such as which side the sage will come from in tractate Eruvin). So there too we are not talking about a hidden reality. And in general, a hidden reality is not retroactive clarification. If a child is born to me while I’m abroad and therefore I don’t know its sex, then when I am informed that it’s a boy, nothing is clarified retroactively. That does not belong to the Talmudic topic of retroactive clarification. Retroactive clarification is always an action backward in time. And so too with a condition formulated as “on condition that,” at least according to Rabbi Isaac in Tosafot on Ketubot 74.