How many descendants did Abraham give rise to?

Question

In Genesis 22 there is a divine oath that seems to suggest that Abraham's descendants will be way more numerous than has yet been realize:

Berean Study Bible Genesis 22: 16 and said, "By Myself I have sworn, declares the LORD, because you have done this thing and have not withheld your son, your only son, 17 indeed I will greatly bless you, and I will greatly multiply your seed as the stars of the heavens and as the sand which is on the seashore; and your seed shall possess the gate of their enemies.

A very literal reading would put that number as 10 to the 22nd power (which is the current scientific estimate for both the number of stars in the visible universe and, coincidentally, of the sands of the seashore, according to:

https://youtu.be/2-UuWx8zCYw?t=2m30s

Just how numerous are the descendants so far in total since the oath?

And a related question would be whether or not there is any Rabbinic discussion as to whether or not there will be an end to the increase of the number of Jews. In other words, does the oath suggest that the People will continue to multiply forever?

Answer 1

First of all this refers to the descendants of Yitzchak, not the other children of Avraham because as it says in Vayera 21:12

וַיֹּ֨אמֶר אֱלֹהִ֜ים אֶל־אַבְרָהָ֗ם אַל־יֵרַ֤ע בְּעֵינֶ֨יךָ֙ עַל־הַנַּ֣עַר וְעַל־אֲמָתֶ֔ךָ כֹּל֩ אֲשֶׁ֨ר תֹּאמַ֥ר אֵלֶ֛יךָ שָׂרָ֖ה שְׁמַ֣ע בְּקֹלָ֑הּ כִּ֣י בְיִצְחָ֔ק יִקָּרֵ֥א לְךָ֖ זָֽרַע:

And God said to Abraham, "Be not displeased concerning the lad and concerning your handmaid; whatever Sarah tells you, hearken to her voice, for in Isaac will be called your seed.

Secondly, as the meforshim point out, this is a figurative statement which means that the Bnai Yisrael will be existing forever just like the stars and the sand. As the Art Scroll Chumash cites on 22:17

When Israel complies with Hashem's will, they resemble the stars of heaven; then no one can dominate them. But when they flout his will, they resemble the sand of the seashore - trampeled by every tyrannical foot. (Midrash Or HaAfelah)

Another point is that the stars and sand are not countable, not because of the numbers but because they are seen as a group and the individual members of that group cannot be completely identified. It is as a group that the significance shows (like the entire sea shore) even though there are individuals who show up (like the brightest stars). Consider a group of stars which is visible to the naked eye but as more and more attention is given with higher powered telescopes more and more detail can be discovered.

Note that Tehillim 147:4

He counts the number of the stars; He calls them all by name.

Means that Hashem (alone) is capable of knowing and understanding each individual element in the Universe that He created as well as maintaining everything in its correct relationship with everything else. This too can be an analogy with Bnai Yisrael, being as the stars in the heaven. Only Hashem understands and Knows each individual person as well as the group that those individuals make up.

Answer 2

The answer was already addressed by @sabbahillel. I would like to point out though that scientists use the term 'visible' universe to not mean 'what you can see with your naked eye'. Scientists use this term to describe the universe in terms of the speed of light - i.e. the maximum physical limits light can travel.

The term visible thus is misleading. It does not at all refer to stars you can 'see' with your naked eye, but rather the whole gamut of the universe as far as light can travel.

Wikipedia notes:

The observable universe is a spherical region of the Universe comprising all matter that can be observed from Earth at the present time, because electromagnetic radiation from these objects has had time to reach Earth since the beginning of the cosmological expansion. There are at least 2 trillion galaxies in the observable universe. Assuming the Universe is isotropic, the distance to the edge of the observable universe is roughly the same in every direction. That is, the observable universe has a spherical volume (a ball) centered on the observer. Every location in the Universe has its own observable universe, which may or may not overlap with the one centered on Earth.

The word observable in this sense does not refer to the capability of modern technology to detect light or other information from an object, or whether there is anything to be detected. It refers to the physical limit created by the speed of light itself. Because no signals can travel faster than light, any object farther away from us than light could travel in the age of the Universe (estimated as of 2015 around 13.799±0.021 billion years) simply cannot be detected, as they have not reached us yet. Sometimes astrophysicists distinguish between the visible universe, which includes only signals emitted since recombination—and the observable universe, which includes signals since the beginning of the cosmological expansion (the Big Bang in traditional physical cosmology, the end of the inflationary epoch in modern cosmology).

In any event, the Torah tells us that Hashem told Avrohom Avinu to look up at the stars and to theoretically count them. The commentators (includ. Rashi) explain that Avrohom Avinu was told to look at his astrology charts to show him that Avrohom Avinu and his family would be above the stars, i.e. they would not be governed by the natural order of the world, but be able to break beyond that.)

On a very simple level then, Avrohom Avinu would have seen approximately 6000 stars give or take a few hundred, depending on his location and visibility (see Sky and Telescope).

So while it is a nice thought that the number of stars is 10^22, it doesn't seem to me that this figure was part of the equation. Avrohom Avinu did not have a hubble-space telescope to tell him the number of stars in the observable universe!