When did the events in לך לך happen?

If you just read parshas לך לך you would think that first Hashem told Avraham to go to Eretz Yisroel, then came the story with לוט, the 4 kings, etc. and then came the ברית בין הבתרים. However, the Tosafos (and other Rishonim) point out that if we take a closer look at the chronology from the medrashim we see that this is not true.

Hashem tells Avraham by the ברית בין הבתרים that his descendents will be in golus 400 years. Rashi points out that they were only in Egypt 210 years and therefore explains based on the medrashim that the 400 years started with the birth of Yitzchak. However, the Torah says in Parshas Bo that they were in Egypt 430 years. Rashi there explains (again based on medrashim) that the extra 30 years is from the ברית בין הבתרים, in other words the ברית בין הבתרים was 30 years before Yitzchak was born. We know that Yitzchak was born when Avraham was 100 years old which means that ברית בין הבתרים had to be 30 years earlier when Avraham was 70. However, at the beginning of parshas לך לך the Torah tells us that Avraham was 75 years old when he left Charan. This means that לך לך had to be 5 years after the ברית בין הבתרים. Tosafos in Shabbos 10b makes this calculation and says this is what happened. Avraham came to EY when he was 70 and went through the ברית בין הבתרים, and then he returned to Charan for 5 years until Hashem told him לך לך.

However, this is very strange for a number of reasons:

1. Why did Avraham come to Israel at the age of 70 and then leave?
2. לך לך was not the first time Avraham left his homeland, he already did it once before at the age of 70
3. Rashi and the medrashim make it out as if Avraham had no idea where he was going when Hashem told him לך לך, yet he had already been there.
4. Why would the Torah wrote the story in a backwards order? 

When was Moshiach supposed to have come?

Based on the Gemara Sanhedrin 97 and the pesukim in Daniel, the Rishonim and Acharonim come up with various times that Moshiach was supposed to have come. Every single one of them has long since passed.

1. Rashi - 978
2. Yad Ramah - 803
3. R' Sadya Gaon - 983
4. Rambam (Iggeres Teiman) - 1212
5. Ramban (in his famous debate) - 1358
6. Malbim - offers a number of possibilities
1. 590
2. 1913
3. 1928 - He suggested that the Geula would start in 1913 and complete in 1928

Yet we are supposed to believe that Moshiach is still coming.

How tall was Avraham Avinu?

In this weeks Parsha we are introduced to Avraham Avinu. Maseches Sofrim states the following:

"The man [who lived in Chevron] was the greatest of the giants" (Yehoshua 14:15) -- This refers to our forefather Avraham, whose height was equal to that of seventy-four men. The amount of food and drink he consumed was enough for seventy-four men, and he had the strength of that many men as well.

R' Chaim Kanievsky is his sefer on Tanach (טעמא דקרא) takes this medrash literally and in fact offers an explanation of the source.

However, it is clear that from a scientific basis it is absolutely impossible for a human being to be that tall.

The size that a person could grow to is limited by the strength of materials (particularly bone) and gravity. A person's size is ultimately limited by the cube square law. For simplicity's sake let's model a person as a box. A box's volume is a product of length x height x width so a box that has a length, width and height of 5 feet (our person model) will have a volume of 125 feet cubed. Now assume that he grows to 4x times these proportions (20x20x20). He will now have a volume of 8000 cubic feet, in other words quadrupling his length increases his volume by a factor of 64. Now we need to consider density and mass. It makes sense to say as a person grows his density stays the same (otherwise he would simply thin out into nothingness). To maintain a constant density means that mass must increase at the same rate as volume so quadrupling height increases weight by a factor of 64. The problem is that as weight increases the ability of the skeleton to support that weight does not. The strength of an object depends on how wide it is, it's cross-sectional area. In our case here volume and mass increase much faster then the cross -sectional area of the bones.

Let's take the following simple example of someone who is 6 feet tall and 185 pounds. A single vertebra can support approximately 800 pounds. Now lets increase his height by a factor of 10 to 60 feet. His volume and mass grow by 1000 while his cross-sectional area only grows by a factor of 100. His vertebra can now support 80,000 pounds but his weight is now 185,000 pounds, meaning that his skeleton can no longer support his weight.

The bottom line is that if Avraham Avinu was 74 times taller then the average man (between 370 and 444 feet tall) his body would collapse of it's own weight (well before 74 times). It is a matter of simple physics.

How long will the Messianic period last?

Belief in the Messiah is one of the 13 principles of faith. However, when the Messiah will come and how long the messianic period will last is the subject of dispute. The gemara (Sanhedrin 99) offers the following suggestions for how long the Messianic period will last:

1. R' Eliezer - 40 years
2. R' Dosa - 400 years
3. Rebbi - 365 years
4. Avimi - 7000 years
5. R' Yehuda - the amount of time from creation until the Messiah comes
6. R' Nachman Bar Yitzchak - the amount of time from the flood until the Messiah comes

Interestingly enough the Gemara earlier stated that the world will last 6000 years, 

Sanhedrin 96B - Six thousand years were decreed upon the world: 2000 years of emptiness (without Torah), 2000 years of Torah, and 2000 years for Mashi'ach. This opinion of 6000 years is generally accepted, however, opinions 4-6 above clearly disagree with this.

The conclusion that we can draw from this is that like with many things Chazal had no clue about how long the messianic period will last and the numbers range from 40 - 7000 quite a large discrepancy. Considering that belief in Messiah is a principle of faith it is astounding that there is such a wide range of opinions. Of course, if Chazal had no clue about the Messiah what else did they have no clue about?