Wednesday, May 06, 2009

Cool Cell Movie

In grade school, the picture of the cell we are given is quite simplistic. The real cell is anything but. Here is a really cool animation depicting parts of the cell. Truly a marvel of Hashem!

Click here to view!

Friday, April 03, 2009

Saying a Beracha on a River Formed After Creation

Just a quick interesting halachic issue I found. Everyone knows that on a large impressive river, one says the beracha "oseh maaseh bereshis". However, what I didn't know was that there is a condition on this beracha:

According to Artscroll Yerushalmi Berachos 88b1-2 footnote 11, the Pri Megadim to Magen Avraham says that one may NOT recite the beracha of "maaseh oseh bereshis" on a river unless the river has always been there since the time of Creation. I.e. if there was a large earthquake/volcano/atom bomb that caused a new river to form today, then we would not say the beracha upon seeing such a "new" river. Also, if we purposefully change or add to a river (like a canal), then we cannot say the beracha on the new part of the river.

The question arises that if one holds like the authorities (mostly kabbalists) that say that the world is very ancient (on time scales like those that scientists have determined), then it is possible that we could never say this beracha. Since according to geologists, the Earth has gone through huge changes over time, any river we see today is likely not to have existed in the distant past. (For example, during the ice ages, and especially during the gathering of the first water on Earth).

It would seem one would have to say that the Creation is not considered truly completed until Adam Harishon was formed. According to that, (and the opinions that the world simply looks old but in reality is only as old as the time of Adam Harishon), we would need to determine if any particular river was around for the last 6000 years before we could say a beracha upon seeing it. It would be interesting to see if it is halachically permissible to use the findings of geologists to make such determinations.

Friday, March 06, 2009

Scientific Techeles Gematria

I already had this on my web site before I started this blog, but I realized today that I have no link to it anymore (and I am very tired). So, rather then retype it, here is the link:

Techeles Gematria

It is an interesting gematria that I came across in yeshiva. Basically, if you combine some gematrias of the word techeles, and then convert that number (assuming it is in units of amos (~18 inch)) into nano-meters, you get the maximum absorption frequency of light of indigotin (in the visible range), which is the chemical composition of the dye from the murex trunchulus snail (and the indigo plant). Take a look!

Friday, February 06, 2009

When is the Gender of an Unborn Child Determined?

The mishnah in Berachos Chapter 9 says:
One who cries out for that which is past - this is prayer in vain. How so? His wife is pregnant, and he says, "May it be Your will that my wife give birth to a male," - this is a prayer in vain.
It would seem at first glance that this implies that the gender of the child is determined before a woman (or perhaps her husband) notices that she is pregnant. However, this seems not to be the case, for the Yerushalmi says:
The academy of Yanni say: The Mishnah was speaking about a woman on the birthing stool. But before that point, one may pray [for the gender] in accordance with "Behold, as clay in the hand of the potter...."
This implies that the gender is not set until right before birth! And further, in Midrash Bereishis Rabba 72:6 we see the opinion of R' Yehudah ben Pazi who says that even on the birthing stool the fetus can be transformed, and thus one can still pray.

Most people today go by the rule that up to 40 days, one can pray for the gender, but not after that. [I have not yet found the source for this.]

According to modern science, the gender of the child is determined at conception (although I remember seeing something to the effect that there is a possibility of gender change at the very beginning of pregnancy, but I cannot recall where I read about it). This seems to contradict the gemara's interpretation of the Mishnah in Berachos.

However, it does not necessarily. There is a concept in the gemara that one should not count his grain too much, because then G-d will not cause a miracle and give him more. Meaning, that G-d does not want to do open miracles, but hidden ones He does. Therefore, if no one has detected the gender of the child, it would seem that G-d could perform a hidden miracle of changing the gender all the way through pregnancy. (However, today, with ultrasound, it would seem we cut this time down quite a bit - once we detect the gender, a gender change would be an open miracle). This would explain the Gemara's opinion of the Mishnah, that the prayer in vain refers to the time during birth, i.e. where the gender can be observed for the first time.

However, there is a source in Chazal that gender is determined at conception. The Midrash Tanchumah, Parashahs Pekudeh, sif 3 discusses what happens during conception and says that G-d tells a certain angel to go down and protect the droplet, and cultivate it into 365 parts. After doing so the angel shows the drop to G-d and says:
"I have done just as You have commanded me, so what has been decreed for this droplet?" The Holy One, Blessed is He, immediately decrees the destiny of the droplet; if it will be male or female, weak or strong, ...
This Midrash is seemingly saying that the gender is decreed at conception! If this is the case, then perhaps (unless this goes against psak halachah) one could take this view and say that indeed gender is determined at conception, and explain the Mishnah above accordingly.

Friday, January 09, 2009

The Number of Stars in the Universe

As is mentioned in many outreach lectures, the Gemara in Berachos 32B says the following:

Hashem said to her (Israel): My daughter, 12 mazalos did I create in the rakia, and for each one I created 30 hosts. For each host, I have created 30 legions, for each legion I have created 30 cohorts, for each cohort I have created 30 maniples, for each maniple I have created 30 camps. To each camp I have hung365,000 myriads (10,000s) of stars corresponding to the days of the solar year. All of them I created for your sake.

This Gemara seems to be telling us how many stars there are in the rakia (which I have found is best defined as the view of the sky from the Earth). It is obviously rounding the number off because it was well known when this was written that the solar year is a bit longer than 365.25 days.

If you multiply out the groups, you get a total of 1.06434X10^18 stars. As many point out, this is within a few orders of magnitude of the current scientific estimates of the number of stars in the visible universe.

I thought I would add a bit to this idea as follows:

First, according to this Gemara, it is only mentioning the 12 mazelos of the zodiac. The zodiac covers a 16 degree band across the sky. Therefore for the total number in the whole sky, you must compute the surface area of the 16 degree band and apply the stars-per-degree^2 to the rest of the celestial sphere. This is pretty straight-forward, and one finds that the whole sky (assuming the same star density) yields 7.6476 X 10^18 stars.

Now, according to sceintific studies, there are anywhere from 10^21 -> 7 X 10^22 stars in the observable universe. These numbers are computed by taking a small strip of the sky, and counting the number of galaxies in that strip, and then assuming each galaxy has an average number of stars similar to our own Galaxy. They then use this to estimate the whole universe. This can be problematic for a couple for reasons.

First, besides the fact that we don't know how many stars are in earlier galaxies, we also don't know if we are seeing different galaxies to begin with. This is because through the bending of light around other galaxies, sometimes you can see two or more images of the same galaxy. This is referred to as an "Einstein Ring." Now, we can detect these, but it is entirely possible that there are other lensing effects we can't immediately detect. This phenomena reduces the number of galaxies in any view of the sky. Also along these lines are topological concerns. There is debate about the shape of the universe, but it seems that it is flat. This means that if the universe is finite (which is accepted) then the universe behaves like a pacman game in that if you fly too far in one direction, you will loop around and come back to where you started. With this in mind, it is possible that some the the most distant galaxies we see are actually the same galaxies we see elsewhere.

Second, assuming each patch of sky is equal to the others is highly extrapolative. A perfect example of why is found here. In this article it describes a huge, vast empty "hole" in the universe devoid of stars and galaxies that was not noticed previously. How many other holes there are we may never know for sure. These "holes" reduce the estimated number of galaxies in the universe even more, and if there are enough of them, could invalidate the extrapolation of one patch of sky to the next.

With all this in mind, the difference of 7 X 10^18 and 7 X 10^22, while enormous, is not conclusive. (For a quick example, say we find out that most old galaxies only have about 10^9 (1 billion) stars and that there are really only about 10 billion unique galaxies, then the number comes to 10^19.)