Avshalom C. Elitzur

The emergence of life on Earth.

Combined top-down and bottom-up research strategies and the principle of biological continuity were employed in an attempt to reconstruct a comprehensive origin of life theory, which is an extension of the coevolution theory (Lahav and Nir, Origins of Life Evol. Biosphere (1997) 27, 377-395). The resulting theory of emergence of templated-information and functionality (ETIF) addresses the emergence of living entities from inanimate matter, and that of the central mechanisms of their further evolution. It proposes the emergence of short organic catalysts (peptides and proto-ribozymes) and feedback-loop systems, plus their template-and-sequence-directed (TSD) reactions, encompassing catalyzed replication and translation of populations of molecules organized as chemical-informational feedback loop entities, in a fluctuating (wetting-drying) environment, functioning as simplified extant molecular-biological systems. The feedback loops with their TSD systems are chemically and functionally continuous with extant living organisms and their emergence in an inanimate environment may be defined as the beginning of life. The ETIF theory considers the emergence of bio-homochirality, a primordial genetic code, information and the incorporation of primordial metabolic cycles and compartmentation into the emerging living entities. This theory helps to establish a novel measure of biological information, which focuses on its physical effects rather than on the structure of the message, and makes it possible to estimate the time needed for the transition from the inanimate state to the closure of the first feedback-loop systems. Moreover, it forms the basis for novel laboratory experiments and computer modeling, encompassing catalytic activity of short peptides and proto-RNAs and the emergence of bio-homochirality and feedback-loop systems.

Subtle differences in structural transitions between poly-L- and poly-D-amino acids of equal length in water

Mirror-image asymmetric molecules, i.e., chiral isomers or enantiomers, are classically considered as chemically identical. Recent studies, however, have indicated that parity violation by the nuclear weak force induces a tiny energy difference between chiral isomers. Upon combination with a massive amplification process, expansion of this difference to a detectable macroscopic level may be achieved. Yet, experimental tests of this possibility, where one enantiomer is compared to the other in solution, are hampered by the possible presence of undetectable impurities. In this study we have overcome this problem by comparing structural and dynamic features of synthetic D- and L-polyglutamic acid and polylysine molecules each of 24 identical residues. In these water-soluble polypeptides helix formation is an intramolecular autocatalytic process amplified by each turn, which is actually unaffected by low level of putative impurities in the solvent. The helix and random coil configurations and their transition were determined in this study by circular dichroism (CD) and isothermal titration calorimetry (ITC) in water and deuterium oxide. Distinct differences in structure and transition energies between the enantiomeric polypeptides were detected by both CD and ITC when dissolved in water. Intriguingly, these differences were by and large abolished in deuterium oxide. Our findings suggest that deviation from physical invariance between the D- and L-polyamino acids is induced in part by different hydration in water which is eliminated in deuterium oxide. Based on the recent findings by Tikhonov and Volkov (V. I. Tikhonov and A. A. Volkov, Science 2002, 296, 2363) we suggest that ortho-H(2)O, which constitutes 75% of bulk H(2)O, has a preferential affinity to L-enantiomers. Differential hydration of enantiomers may have played a role in the selection of L-amino acids by early forms of life.

Nonlocal effects of partial measurements and quantum erasure

Partial measurement turns the initial superposition not into a definite outcome but into a greater probability for it. The probability can approach 100%, yet the measurement can undergo complete quantum erasure. In the Einstein-Podolsky-Rosen ~EPR! setting, we prove that ~i! every partial measurement nonlocally creates the same partial change in the distant particle, and ~ii! every erasure inflicts the same erasure on the distant particle’s state. This enables an EPR experiment where the nonlocal effect does not vanish after a single measurement but keeps ‘‘traveling’’ back and forth between particles. We study an experiment in which two distant particles are subjected to interferometry with a partial ‘‘which path’’ measurement. Such a measurement causes a variable amount of correlation between the particles. A new inequality is formulated for same-angle polarizations, extending Bell’s inequality for different angles. The resulting nonlocality proof is highly visualizable, as it rests entirely on the interference effect. Partial measurement also gives rise to a new form of entanglement, where the particles manifest correlations of multiple polarization directions. Another novelty in that the measurement to be erased is fully observable, in contrast to prevailing erasure techniques in which it can never be observed. Some profound conceptual implications of our experiment are briefly pointed out.

Is There More to T

We present some novel results indicating that times description in present-day physics is deficient. We use Hawkings information-erasure hypothesis to counter his own claim that times arrow depends only on initial conditions. Next, we propose quantum mechanical experiments that yield inconsistent histories, suggesting that not only events but also entire histories might be governed by a more fundamental dynamics.

When one quantum object is measured by another: a new class of quantum paradoxes

Nearly all quantum experiments involve a classical object (a macroscopic apparatus) measuring a quantum mechanical one (a particle). In the Elitzur-Vaidman bomb-testing experiment the roles have been reversed, and a surprising result ensued. Later, Hardy expanded this method and allowed two and three particles to measure one another before the macroscopic apparatus made the final measurement, obtaining even more intriguing results. Recently, we elaborated this experimental paradigm further, increasing the number of particles that measure one another. The results seem to violate basic notions of space and time. In one experiment, the wave function appears to proceed in space non-sequentially. In the other experiment, entanglement ensues between particles that seem to have never interacted, giving the impression of an inconsistent history. We survey this family of experiments and discuss its implications.