Paul Joseph Steinhardt (born December 25, 1952) is an American theoretical physicist whose principal research is in cosmology and condensed matter physics.

[4] He subsequently led a separate team that followed up that discovery with several more examples of natural quasicrystals recovered from the wilds of the Kamchatka Peninsula in far eastern Russia.

Several years later, he and collaborators reported the accidental synthesis of a previously unknown type of quasicrystal in the remnants of the first atomic bomb test on July 16, 1945, at Alamagordo, New Mexico.

Hubble friction played a critical role in the 1983 paper by James Bardeen, Steinhardt and Michael S. Turner[11] who were the first to introduce a reliable, relativistically gauge invariant method to compute how quantum fluctuations during inflation might naturally generate a nearly scale-invariant spectrum of density fluctuations with a small tilt, properties later shown by observations of the cosmic microwave background to be features of our universe.

Although some cosmologists would later come to embrace the multiverse, Steinhardt consistently expressed his concern that it utterly destroys the predictive power of the theory he helped create.

Bond, G. Efstathiou and Steinhardt performed the first calculations of the complete imprint of gravitational waves on the B-mode temperature maps and on the polarization of the microwave background radiation.

[18] The unlikeliness problem: In 2013, Anna Ijjas, Abraham Loeb and Steinhardt added to the criticisms in a widely discussed pair of papers that the inflationary model was much less likely to explain our universe than previously thought.

The hypothetical idea that the universe began with a bang is based on extrapolating back in time, assuming that Einstein's equations of general relativity remain valid at energies and temperatures far greater than have ever been tested.

These fluctuations would have caused space-time to curve and warp and the distribution of energy to become very uneven, all of which is inconsistent with what experimentalists observe when they study the early universe.

By evading the infamous cosmic singularity problem associated with a big bang, a bounce avoids quantum gravity effects that produce an unsmooth universe.

A natural extension of these ideas is a never-beginning and never-ending cyclic universe in which epochs of bounce, expansion, and contraction repeat at regular intervals.

The fiery collision and rebound of these branes is comarable to a big crunch, a violent event that would depend sensitively on strong quantum gravity effects that are not yet established and may create tremendous curvature and warping of spacetime.

They do not require extra dimensions or branes or string theory; ordinary fields with potential energy evolving in space-time, similar to inflationary models, can be used.

Universal smoothing and ultralocality: To test these ideas, Anna Ijjas adapted the tools of numerical general relativity, originally invented to simulate the merger of black holes and the emission of gravitational waves, to cosmology.

Beginning from wildly unsmooth and curvy starting condition, the studies verified that slow contraction smooths virtually all of spacetime due to an effect of general relativity known as ultralocality.

[33] Evidence from the LHC suggests that the current vacuum may decay in the future, according to calculations made by Steinhardt, Turok and Itzhak Bars.

The 2018 paper on swampland conjectures with Agrawal, Obieds and Vafa[22] points to quintessence as being the only option for dark energy in string theory and consistent quantum gravity.

[39] In 2014, Steinhardt, Spergel and Jason Pollack have proposed that a small fraction of dark matter could have ultra-strong self-interactions, which would cause the particles to coalesce rapidly and collapse into seeds for early supermassive black holes.

The new theory overturned 200 years of scientific dogma and proved that quasicrystals could violate all of the previously accepted mathematical theorems about the symmetry of matter.

The first reported example of a synthetic quasicrystal: Working simultaneously to, but independently of, Steinhardt and Levine, Dan Shechtman, Ilan Blech, Denis Gratias and John Cahn at the National Bureau of Standards (NBS) were focused on an experimental discovery they could not explain.

It was an unusual alloy of manganese and aluminum with a diffraction pattern of what appeared to be sharp (though not perfectly point-like) spots arranged with icosahedral symmetry that did not fit any known crystal structure.

[7] Steinhardt and Levine were shown a preprint of the Shechtman team's paper and immediately recognized that it could be experimental proof of their still-unpublished quasicrystal theory.

It proved to be unstable and the noted imperfections in the diffraction pattern allowed for multiple explanations (including one about crystal twinning proposed by Linus Pauling) that were hotly debated for the next few years.

[7] In 1987, An-Pang Tsai and his group at Japan's Tohoku University made an important breakthrough with the synthesis of the first-ever stable icosahedral quasicrystal.

The team, composed of Peter Lu, Ken Deffeyes and Nan Yao, devised a novel mathematical algorithm to search through an international database of powder diffraction patterns.

On January 2, 2009, Steinhardt and Nan Yao, director of the Princeton Imaging Center, examined the material and identified the signature diffraction pattern of an icosahedral quasicrystal.

The team included Bindi and Valery Kryachko, the Russian ore geologist who had found the original samples of khatyrkite crystal while working at the Listventovyi stream in 1979.

It was accepted by the International Mineralogical Association and named "steinhardtite" in Steinhardt's honor[46] In 2015, a second type of natural quasicrystal was discovered in a different grain of the same meteorite.

"[47][48] Three more crystalline minerals were also discovered and named after colleagues involved in Steinhardt's quasicrystal research: "hollisterite," for Princeton petrologist Lincoln Hollister; "kryachkoite," for Russian geologist Valery Kryachko; and "stolperite," for Caltech's former provost Ed Stolper.

[62][63] Working with David Nelson and Marco Ronchetti, Steinhardt formulated mathematical expressions, known as "orientational order parameters", for computing the degree of alignment of interatomic bonds in liquids and solids in 1981.