The story so far: A few months ago, I published my monograph The Sun's Path at Night, which discusses the Sages' view that the sun passes behind the sky at night - with the sky being believed to be a solid dome. It emerged that ALL of the Rishonim without exception, as well as many Acharonim, agreed that Chazal held this view. Only beginning with figures such as Maharal and Ramchal did people attempt to reinterpret Chazal - but there is no reason not to accept that the view of all the Rishonim and many Acharonim is correct.
Then, I pointed out that Chazal's belief in a firmament was not merely of halachic interest to them, but was also how they interpreted the Torah itself, in its mention of the rakia and Shamayim. In a follow-up post, I brought a number of sources which elaborated upon Chazal's view of the firmament, as well as showing how they derived these ideas from the pesukim. For example:
Rabbi Yudeh ben Pazi said: ["Let there be a rakia" means] "Let the rakia become like a cloth." This is just as it is said, "They flattened out (וירקעו) sheets of gold" (Shemos 39:3).
It was taught in the name of Rabbi Yehoshua: The thickness of the firmament is as the width of two fingers. But the words of Rabbi Chanina dispute this, as Rabbi Acha said in the name of Rabbi Chanina: It says, "Can you help Him tarkia the heavens, firm as a mirror of cast metal?" (Iyov 37:18) - Tarkia means that they were made as a thin sheet of metal (i.e. less than the width of two fingers). I might think that they are not strong - therefore it teaches us, "firm"; I might think that they sag with time, therefore it teaches us "like a mirror of cast metal" - that every moment they appear as freshly cast.
Rabbi Yochanan says: Ordinarily, when a person stretches out a tent, it sags after time; but here, "He stretched [the heavens], like a tent in which to dwell" (Yeshayah 40:22), and it is written "firm" (Iyov ibid.) Rabbi Shimon ben Lakish says: Ordinarily, when a person casts vessels, they eventually rust; but here, "like a mirror of cast metal" - that at every moment, they appear as freshly cast (i.e. as beautiful as when originally made).
Now, all this was deeply problematic for those who oppose the belief in the universe developing over billions of years and evolution due to these notions going against Jewish tradition. For aside from the fact that Jewish rationalist tradition was clearly to interpret Genesis in such a way that we do not need to deny scientific facts, the topic of the rakia presented another argument: That even these staunch traditionalists are going against Jewish tradition in their acceptance that there is no firmament and that Chazal's and the Rishonim's view of the rakia was incorrect.
Their response was to claim that there was no mesorah about the nature of the firmament. Rather, different figures amongst Chazal had different ideas, based on some sort of combination of science and their understanding of Torah, but there was no mesorah about it. In another post, I showed how this was wrong; there was an unequivocal mesorah that there is a firmament - that is to say, a dome above the earth, made of some sort of substantial matter (i.e. not air or space), on the surface of which the sun travels, and which obscures the sun when it passes behind it. This was the universal, uncontested, view of Chazal, based on Pesukim such as that in Iyov 37:18: "Can you spread out the heavens with Him, hard as a mirror of cast metal?" as well as various other usages in Tenach of the root רקע.
And now for the climax: What actually is the rakia?
The answer is that Chazal were absolutely correct. Unlike the anti-rationalists, who (ironically) take the position that Chazal did not know how to learn Tenach and were interpreting the pesukim incorrectly based on mistaken speculation, I think that Chazal were absolutely correct in their interpretation of the pesukim. The etymology of rakia reveals that it clearly refers to a flattened, solid surface. The pesukim in Iyov 37:18 and Yeshayah 40:22 are likewise unequivocal. The Rishonim who defined the etymology of the word rakia, such as Radak and Ibn Janach, also explain it in this way. Finally, I strongly recommend that people read the definite study on this topic which can be freely downloaded, Paul Seely: "The Firmament and the Water Above Part I: The Meaning of raqiaà in Gen 1:6-8," from the Westminster Theological Journal 53 (Fall 1991) 227-240.
As to how to reconcile this with the fact that there is no dome - this is exactly the same challenge as the Scriptural descriptions of the kidneys and heart housing a person's mind, of the dew descending from the heavens, and of the universe developing over six days. The solution is to say that "the Torah speaks as in the language of men," according to how that principle was explained by certain authorities. This approach is not without its own difficulties, but it is necessary and it can be understood in different ways. A full explanation can be found at the end of my monograph on the kidneys. Meanwhile, here is a brief quote from Rav Hirsch:
Jewish scholarship has never regarded the Bible as a textbook for physical or even abstract doctrines. In its view the main emphasis of the Bible is always on the ethical and social structure and development of life on earth; that is, on the observance of laws through which the momentous events of our nation’s history are converted from abstract truths into concrete convictions. That is why Jewish scholarship regards the Bible as speaking consistently in “human language;” the Bible does not describe things in terms of objective truths known only to God, but in terms of human understanding, which is, after all, the basis for human language and expression. (Rabbi Samson Raphael Hirsch, Collected Writings vol. 7 p. 57)
Elsewhere, Rav Hirsch explicitly notes that although there is no actual solid layer surrounding the earth that could be called a firmament, Scripture nevertheless uses that term because that is how the sky appears to man; as a dome over and around the earth (Commentary to Genesis 1:6; cf. Rabbi Akiva Eiger, in his note to the phrase u’vokeya chalonei rakia in Siddur Otzar HaTefillos p. 672, and Maharzav to Midrash Bereishis Rabbah 6:8).
I have no doubt that many people will insist that the word rakia can be understood in a scientifically accurate manner. But as far as I am concerned, they are simply not evaluating the text honestly, due to their religious convictions that nothing in Tenach can be scientifically inaccurate. I discussed this in my post "Modern Orthodox Charedim." I will conclude with a quote from Rav Kook:
It is already adequately known that prophecy takes its metaphors to guide mankind according to that which was then well-known in the language of men at that time, to direct the ear according to that which it is able to hear in its time… The intellectual truths of the depths of Torah are elevated and exalted far beyond these; the human illustrations—whatever they may be—with regard to the nature of existence, certainly also have a particular path in the ethical development of mankind… in each generation, according to his way of framing things, which constantly changes. (R. Avraham Yitzchak Kook, Adar HaYekar, pp. 37-38)