3 ms·

The measurement problem of QM arises only when one tries to define an interaction of a classical measurement device and a quantum system. But everything is quan

by _0w8t 4y ago

The measurement problem of QM arises only when one tries to define an interaction of a classical measurement device and a quantum system. But everything is quantum at the end. So there are no classical devices. In general the appearance of a classical world is unsolved problem in QM. It may well be that answer to the question of why we perceive the world classically will also help to answer the question of why we perceive the direction of time, but since we do not know, one cannot claim the the measurement problem implies the direction of the time. Regarding CPT violation. Even if it was so, it would not imply that one could use it to justify the existence of the time arrow. Asymmetry would imply that one could distinguish the past from future, but it would not explain why what we perceived as the past is the past and not the future. An analogy is a bar that gradually changes from black to white. Surely there is a color gradient. But that alone does not imply that there is a preferred direction from black to white as the choice of the direction is arbitrary.

tsimionescu 4y ago
> The measurement problem of QM arises only when one tries to define an interaction of a classical measurement device and a quantum system. The measurement problem arises when one tries to use QM to predict empirical observations. The concept is fundamental to QM as a physical theory - remove it, and QM can no longer be said to agree with experimental observations (in fact, it contradicts them), so it can no longer be verified to be a physical theory. > But everything is quantum at the end. So there are no classical devices. This remains a supposition. It is possible that the classical world is indeed an emergent phenomenon, as in the many-worlds interpretation for example, but we don't yet have a full, experimentally verifiable account of how that would work. Decoherence has shed some light on aspects of the problem, but it is not enough (it does not account for the choice of observable to measure, the preferred basis problem). > Asymmetry would imply that one could distinguish the past from future, but it would not explain why what we perceived as the past is the past and not the future. Yes, that is a good point. However, moving from the future to the past in SR requires something that can move faster than light (faster than c). Such a particle is in principle possible, but it has negative energy. As such, if such a particle could actually exist, QM would predict that pairs of this particle and regular particles would form all the time in the void, and thus the universe would quickly become pure chaos (this prediction comes from the observation that energy is conserved if in a region of 0 energy you create a particle with energy E and one with energy -E). So, if we can establish that the future and the past are distinguishable, then relativistic quantum mechanics requires that movement is only possible from the past to the future, and this should give us an arrow of time even at the microscopic level.

by _0w8t 4y ago

tsimionescu 4y ago

> The measurement problem of QM arises only when one tries to define an interaction of a classical measurement device and a quantum system. The measurement problem arises when one tries to use QM to predict empirical observations. The concept is fundamental to QM as a physical theory - remove it, and QM can no longer be said to agree with experimental observations (in fact, it contradicts them), so it can no longer be verified to be a physical theory. > But everything is quantum at the end. So there are no classical devices. This remains a supposition. It is possible that the classical world is indeed an emergent phenomenon, as in the many-worlds interpretation for example, but we don't yet have a full, experimentally verifiable account of how that would work. Decoherence has shed some light on aspects of the problem, but it is not enough (it does not account for the choice of observable to measure, the preferred basis problem). > Asymmetry would imply that one could distinguish the past from future, but it would not explain why what we perceived as the past is the past and not the future. Yes, that is a good point. However, moving from the future to the past in SR requires something that can move faster than light (faster than c). Such a particle is in principle possible, but it has negative energy. As such, if such a particle could actually exist, QM would predict that pairs of this particle and regular particles would form all the time in the void, and thus the universe would quickly become pure chaos (this prediction comes from the observation that energy is conserved if in a region of 0 energy you create a particle with energy E and one with energy -E). So, if we can establish that the future and the past are distinguishable, then relativistic quantum mechanics requires that movement is only possible from the past to the future, and this should give us an arrow of time even at the microscopic level.