Person

Nachmanides

Moses ben Nahman (1194-1270), the Ramban, Catalan rabbi, talmudist, philosopher, kabbalist, physician, and biblical exegete, one of the most influential medieval Jewish interpreters and the major rabbinic anticipator of long-age cosmology in his commentary on Genesis 1. His reading of the six creation days as "days of the Holy One, blessed be He", phases of cosmological development from the divine reference frame, not 24-hour periods from a human reference frame, became the most-cited rabbinic warrant for Old-Earth and Day-Age readings in modern Jewish and Christian concordism. Hugh Ross cites him extensively. Gerald Schroeder's relativistic-time framework is in conscious continuity with him.

Biography

Born 1194 in Girona (Gerona), Catalonia, in the Crown of Aragon. Hebrew name Mosheh ben Nahman; Catalan name Bonastruc ça Porta.
Trained as a rabbi, talmudist, philosopher, kabbalist (under Isaac the Blind's circle), and physician. The kabbalistic education distinguishes him sharply from the philosopher-rationalist Maimonides.
1232-1235, plays a moderating role in the Maimonidean Controversies (the conflict over whether Maimonides's rationalist philosophical program was compatible with traditional Jewish piety). Nachmanides defends Maimonides against the ban while distancing himself from full-blown Aristotelianism, a characteristic middle path.
1263, the Disputation of Barcelona (Hebrew: Vikuach Barcelona). King James I of Aragon orders a formal disputation between Nachmanides and the Dominican convert Pablo Christiani (a former Jew) on Christian claims about messianic prophecy and Talmudic acknowledgment of Christ. The disputation lasts four days. Nachmanides argues, uniquely freely, having been granted royal protection for the duration, that the Talmud's aggadic statements about the Messiah are not binding (the methodological move of distinguishing aggadah from halakhah), that the prophetic-messianic texts are not necessarily fulfilled by Jesus, and that the messianic kingdom of universal peace prophesied in Isaiah 2 and Micah 4 has manifestly not arrived. Nachmanides publishes his own account of the disputation; King James praises him publicly; the Dominicans appeal to the pope (Clement IV) demanding punishment.
1267, forced into exile by the consequences. Travels to the Land of Israel; settles in Acre. Visits and restores the long-derelict Jewish community of Jerusalem (the Ramban Synagogue in the Old City still bears his name).
Died 1270 in Acre.

Major works

Commentary on the Torah (begun in Spain, completed in the Land of Israel), his exegetical masterpiece. Combines literal-grammatical exegesis (peshat) with midrashic, philosophical, and kabbalistic readings. The Genesis commentary is the locus of his hexaemeral exegesis.
Commentary on Job, includes the famous excursus on reincarnation (gilgul) drawn from kabbalistic tradition.
Sefer ha-Geulah (Book of Redemption), messianic chronology and eschatology.
Vikuach (Disputation of Barcelona), his own account of the 1263 disputation. Polemical, sharp, and an enduring touchstone in Jewish-Christian polemics.
Talmudic commentaries (Hiddushim), on multiple tractates; sophisticated halakhic analysis in the Tosafist tradition.
Kabbalistic writings, Iggeret ha-Kodesh (disputed attribution), commentary on Sefer Yetzirah, etc.

Key positions

The six days are "days of the Holy One, blessed be He"

The locus classicus, Commentary on Genesis 1:3:

"Yet a great mystery lies in these matters: the six days mentioned in Scripture are the six days of the Holy One, blessed be He, which are long and exceedingly drawn out."

Nachmanides elaborates:

Each "day" is a stage of cosmic development from God's reference frame, not a 24-hour solar day from the human reference frame.
The "days" extend over very long periods of cosmological unfolding.
The framework draws on the rabbinic aggadah (Sanhedrin 97a; Avodah Zarah 9a) that "the world is to exist for six thousand years", six millennia of human history typologically corresponding to the six eras of cosmic creation, followed by the Sabbatical millennium.
Importantly, this is not allegorical evacuation of the days. The days really happened, in real (though divinely-scaled) time. Nachmanides is closer to Hugh Ross's Day-Age than to Augustine's instantaneous creation on this axis.

Six eras → six millennia → seventh-day rest typology

The cosmic-historical pairing:

Cosmic creation day	Millennium of world history	Sabbath analog
Day 1, light	Adam to Noah's flood (millennium 1)	,
Day 2, firmament	Noah to Abraham (millennium 2)	,
Day 3, land/sea/vegetation	Abraham to David (millennium 3)	,
Day 4, luminaries	David to Second Temple (millennium 4)	,
Day 5, fish and birds	Second Temple to Talmud (millennium 5)	,
Day 6, land animals, humanity	Talmud to Messiah (millennium 6)	,
Day 7, Sabbath rest	Messianic age (millennium 7)	Olam Habba

The typological structure is loose at the boundaries but the pattern is firm: cosmic time and world history mirror one another. The six days of creation prefigure the six millennia; the Sabbath of creation prefigures the messianic age.

The "Big Bang" question

Modern Jewish concordists (Aryeh Kaplan, Gerald Schroeder) read Nachmanides as anticipating cosmological insights confirmed only in the 20th century:

Expansion of the universe, Nachmanides reads Gen 1:1 ("the heavens and the earth") as the creation of a primordial substance (hiyuli, from Greek hylē) that then expanded and differentiated into the structures of the cosmos. Schroeder (Genesis and the Big Bang, 1990) treats this as a 13th-century gloss of what 20th-century cosmology calls cosmic inflation / Big Bang expansion.
Single primordial substance, Nachmanides argues all matter derives from one initial bara-act; subsequent days do not involve new creations ex nihilo but the forming and differentiating of the primordial stuff. This maps onto modern cosmological doctrines of the unified initial state.
Time dilation / relativistic-time, Schroeder's framework that the six divine 24-hour days map onto ~15 Gyr of earth-frame time via general-relativistic time dilation is a 20th-century gloss of Nachmanides's "days of the Holy One" reading.

Whether Nachmanides actually anticipated modern cosmology or whether modern advocates retroject onto him is contested (the skeptical reading is that Nachmanides is doing kabbalistic emanation-cosmology in a language that sounds modern-physical only by coincidence). Either way, Nachmanides is the medieval rabbinic anchor for the long-age reading of Genesis 1.

Methodological middle path, between Rashi and Maimonides

Nachmanides occupies a deliberate middle:

Against Rashi's pure-peshat (plain-sense literalism), Nachmanides insists on the deeper (philosophical and kabbalistic) senses.
Against Maimonides's Aristotelian rationalism, Nachmanides insists on the kabbalistic sense and on the integrity of midrash as authoritative tradition (against Maimonides's tendency to allegorize miracles).
For the multi-leveled hermeneutic that became the foundation of the PaRDeS fourfold method: peshat (plain), remez (allusion), derash (homiletical), sod (mystical/kabbalistic).

On miracles and providence

Where Maimonides tends to philosophical-naturalist readings of miraculous narratives, Nachmanides insists that God interacts directly and miraculously with the world, providence is direct and personal, not mediated through impersonal natural-law sequences. This more "supernaturalist" position has appeal across Christian-Jewish lines for its preservation of miracle.

On the Barcelona Disputation

The 1263 Disputation is one of the most important Jewish-Christian theological encounters of the Middle Ages. Three things make it apologetically interesting from the Christian side:

Aggadah/halakhah distinction. Nachmanides successfully argued that the Talmud's aggadic (narrative-homiletical) statements, the kind Pablo Christiani cited to suggest the Talmud acknowledged Jesus as Messiah, are not doctrinally binding. This is a methodological move that has stuck in Jewish-Christian polemics ever since.
The "kingdom hasn't come" objection. Nachmanides' sharpest argument: the messianic prophecies describe universal peace and the end of war (Isa 2:4, Mic 4:3). Manifestly the world after Jesus is still at war. Therefore Jesus has not (yet) fulfilled the messianic prophecies. Christian response: already / not yet, Jesus's first coming inaugurates the kingdom (the spiritual fulfillment, atonement, indwelling Spirit); his second coming consummates it (the political fulfillment, swords to plowshares). The two-stage messianic schema is the standard Christian reply, but it is responding to Nachmanides's challenge. See Messianic Prophecy Probability for the broader prophecy apologetic.
Rabbinic vs ecclesial reading of the Hebrew Bible. Nachmanides' refusal to accept the Christian christological reading of Isaiah 53 ("the Servant is Israel, not the Messiah") became a touchstone Jewish counter-position. Christian response: the corporate reading collapses on the Servant-suffering-for-the-many distinction (Isa 53:8, "for the transgression of my people"; the Servant cannot be Israel suffering for Israel).

The Disputation is relevant to codex entries on Messianic Prophecy Probability and (forthcoming) Isaiah 53 rich hub.

Influence

On medieval rabbinic exegesis, Nachmanides's Torah commentary became one of the four standard medieval commentaries (with Rashi, Ibn Ezra, Sforno). Studied in every traditional yeshiva.
On Kabbalah, Nachmanides is the bridge from the early Catalan-Provençal kabbalistic circles to the later Castilian Zohar tradition. The Zohar (c. 1280) emerges shortly after his death.
On modern Old-Earth / Day-Age Christian apologetics, Hugh Ross (A Matter of Days, 2004; Navigating Genesis, 2014) cites Nachmanides prominently as the medieval Jewish anticipation of the long-age reading. The cross-tradition citation is one of the rhetorically powerful moves in Day-Age apologetics.
On Gerald Schroeder and modern Orthodox-Jewish concordism, Schroeder's Genesis and the Big Bang (1990) and The Science of God (1997) are explicit attempts to formalize Nachmanides's "days of the Holy One" with the mathematics of general-relativistic time dilation.