Daily Archives: February 25, 2021

Study by the University of Bonn determines minimum time for complex quantum operations.

Even in the world of the smallest particles with their own special rules, things cannot proceed infinitely fast. Physicists at the University of Bonn have now shown what the speed limit is for complex quantum operations. The study also involved scientists from MIT, the universities of Hamburg, Cologne and Padua, and the Jlich Research Center. The results are important for the realization of quantum computers, among other things. They are published in the prestigious journal Physical Review X, and covered by the Physics Magazine of the American Physical Society.

Suppose you observe a waiter (the lockdown is already history) who on New Years Eve has to serve an entire tray of champagne glasses just a few minutes before midnight. He rushes from guest to guest at top speed. Thanks to his technique, perfected over many years of work, he nevertheless manages not to spill even a single drop of the precious liquid.

A little trick helps him to do this: While the waiter accelerates his steps, he tilts the tray a bit so that the champagne does not spill out of the glasses. Halfway to the table, he tilts it in the opposite direction and slows down. Only when he has come to a complete stop does he hold it upright again.

Atoms are in some ways similar to champagne. They can be described as waves of matter, which behave not like a billiard ball but more like a liquid. Anyone who wants to transport atoms from one place to another as quickly as possible must therefore be as skillful as the waiter on New Years Eve. And even then, there is a speed limit that this transport cannot exceed, explains Dr. Andrea Alberti, who led this study at the Institute of Applied Physics of the University of Bonn.

In their study, the researchers experimentally investigated exactly where this limit lies. They used a cesium atom as a champagne substitute and two laser beams perfectly superimposed but directed against each other as a tray. This superposition, called interference by physicists, creates a standing wave of light: a sequence of mountains and valleys that initially do not move. We loaded the atom into one of these valleys, and then set the standing wave in motion this displaced the position of the valley itself, says Alberti. Our goal was to get the atom to the target location in the shortest possible time without it spilling out of the valley, so to speak.

First author Manolo Rivera Lam (left) and principal investigator Dr. Andrea Alberti (right) at the Institute of Applied Physics at the University of Bonn. Credit: Volker Lannert/Uni Bonn

The fact that there is a speed limit in the microcosm was already theoretically demonstrated by two Soviet physicists, Leonid Mandelstam and Igor Tamm more than 60 years ago. They showed that the maximum speed of a quantum process depends on the energy uncertainty, i.e., how free the manipulated particle is with respect to its possible energy states: the more energetic freedom it has, the faster it is. In the case of the transport of an atom, for example, the deeper the valley into which the cesium atom is trapped, the more spread the energies of the quantum states in the valley are, and ultimately the faster the atom can be transported. Something similar can be seen in the example of the waiter: If he only fills the glasses half full (to the chagrin of the guests), he runs less risk that the champagne spills over as he accelerates and decelerates. However, the energetic freedom of a particle cannot be increased arbitrarily. We cant make our valley infinitely deep it would cost us too much energy, stresses Alberti.

The speed limit of Mandelstam and Tamm is a fundamental limit. However, one can only reach it under certain circumstances, namely in systems with only two quantum states. In our case, for example, this happens when the point of origin and destination are very close to each other, the physicist explains. Then the matter waves of the atom at both locations overlap, and the atom could be transported directly to its destination in one go, that is, without any stops in between almost like the teleportation in the Starship Enterprise of Star Trek.

In the foyer of the Institute of Applied Physics at the University of Bonn (from left): Thorsten Groh, Manolo Rivera Lam, Prof. Dr. Dieter Meschede and Dr. Andrea Alberti (all at a distance for corona safety reasons). Credit: Volker Lannert/Uni Bonn

However, the situation is different when the distance grows to several dozens of matter wave widths as in the Bonn experiment. For these distances, direct teleportation is impossible. Instead, the particle must go through several intermediate states to reach its final destination: The two-level system becomes a multi-level system. The study shows that a lower speed limit applies to such processes than that predicted by the two Soviet physicists: It is determined not only by the energy uncertainty, but also by the number of intermediate states. In this way, the work improves the theoretical understanding of complex quantum processes and their constraints.

The physicists findings are important not least for quantum computing. The computations that are possible with quantum computers are mostly based on the manipulation of multi-level systems. Quantum states are very fragile, though. They last only a short lapse of time, which physicists call coherence time. It is therefore important to pack as many computational operations as possible into this time. Our study reveals the maximum number of operations we can perform in the coherence time, Alberti explains. This makes it possible to make optimal use of it.

Reference: Demonstration of Quantum Brachistochrones between Distant States of an Atom by Manolo R. Lam, Natalie Peter, Thorsten Groh, Wolfgang Alt, Carsten Robens, Dieter Meschede, Antonio Negretti, Simone Montangero, Tommaso Calarco and Andrea Alberti, 19 February 2021, Physical Review X.DOI: 10.1103/PhysRevX.11.011035

The study was funded by the German Research Foundation (DFG) as part of the Collaborative Research Center SFB/TR 185 OSCAR. Funding was also provided by the Reinhard Frank Foundation in collaboration with the German Technion Society, and by the German Academic Exchange Service.

Read the original post:

Physicists Show a Speed Limit Also Applies in the Quantum World - SciTechDaily

If God wasnt able to break the laws of physics, she arguably wouldnt be as powerful as youd expect a supreme being to be. But if she could, why havent we seen any evidence of the laws of physics ever being broken in the universe?

By Monica Grady

"I still believed in God (I am now an atheist) when I heard the following question at a seminar, first posed by Einstein, and was stunned by its elegance and depth: If there is a God who created the entire universe andall of its laws of physics, does God follow Gods own laws? Or can God supersede his own laws, such as travelling faster than the speed of light and thus being able to be in two different places at the same time? Could the answer help us prove whether or not God exists or is this where scientific empiricism and religious faith intersect, withno true answer? " David Frost, 67, Los Angeles.

*

I was in lockdown when I received this question and was instantly intrigued. Its no wonder about the timing tragic events, such as pandemics, often cause us to question the existence of God: if there is a merciful God, why is a catastrophe like this happening? So the idea that God might be bound by the laws of physics which also govern chemistry and biology and thus the limits of medical science was an interesting one to explore.

If God wasnt able to break the laws of physics, she arguably wouldnt be as powerful as youd expect a supreme being to be. But if she could, why havent we seen any evidence of the laws of physics ever being broken in the universe?

***

Image via The Conversation

This article is part ofThe Conversations new series,Lifes Big Questions, co-published with BBC Future. The series seeks to answer questions about life, love, death and the universe, with the help of professional researchers who have dedicated their lives to uncovering new perspectives on the questions that shape our lives.

***

To tackle the question, lets break it down a bit. First, can God travel faster than light? Lets just take the question at face value. Light travels at an approximate speed of 3 x 105 kilometres every second, or 186,000 miles per second. We learn at school that nothing can travel faster than the speed of light not even the USS Enterprise in Star Trek when its dilithium crystals are set to max.

But is it true? A few years ago, a group of physicists posited that particles called tachyons travelled above light speed. Fortunately, their existence as real particles is deemed highly unlikely. If they did exist, they would have an imaginary mass and the fabric of space and time would become distorted leading to violations of causality (and possibly a headache for God).

It seems, so far, that no object has been observed that can travel faster than the speed of light. This in itself does not say anything at all about God. It merely reinforces the knowledge that light travels very fast indeed.

Things get a bit more interesting when you consider how far light has travelled since the beginning. Assuming a traditional big bang cosmology and a light speed of 3 x 105 km/s, then we can calculate that light has travelled roughly 1024 km in the 13.8 billion years of the universes existence. Or rather, the observable universes existence.

The universe is expanding at a rate of approximately 70km/s per Mpc (1 Mpc = 1 Megaparsec ~ 30 million km), so current estimates suggest that the distance to the edge of the universe is 46 billion light years. As time goes on, the volume of space increases, and light has to travel for longer to reach us.

There is a lot more universe out there than we can view, but the most distant object that we have seen is a galaxy, GN-z11, observed by the Hubble Space Telescope. This is approximately 1023 km or 13.4 billion light years away, meaning that it has taken 13.4 billion years for light from the galaxy to reach us. But when the light set off, the galaxy was only about 3 billion light years away from our galaxy, the Milky Way.

We cannot observe or see across the entirety of the universe that has grown since the big bang because insufficient time has passed for light from the first fractions of a second to reach us. Some argue that we therefore cannot be sure whether the laws of physics could be broken in other cosmic regions perhaps they are just local, accidental laws. And that leads us on to something even bigger than the universe.

The multiverse

Many cosmologists believe that the universe may be part of a more extended cosmos, a multiverse, where many different universes co-exist but dont interact. The idea of the multiverse is backed by the theory of inflation the idea that the universe expanded hugely before it was 10-32 seconds old. Inflation is an important theory because it can explain why the universe has the shape and structure that we see around us.

But if inflation could happen once, why not many times? We know from experiments that quantum fluctuations can give rise to pairs of particles suddenly coming into existence, only to disappear moments later. And if such fluctuations can produce particles, why not entire atoms or universes? Its been suggested that, during the period of chaotic inflation, not everything was happening at the same rate quantum fluctuations in the expansion could have produced bubbles that blew up to become universes in their own right.

Are we living in a bubble universe? Image via The Conversation/Juergen Faelchle/Shutterstock

But how does God fit into the multiverse? One headache for cosmologists has been the fact that our universe seems fine-tuned for life to exist. The fundamental particles created in the big bang had the correct properties to enable the formation of hydrogen and deuterium substances that produced the first stars.

The physical laws governing nuclear reactions in these stars then produced the stuff that lifes made of carbon, nitrogen and oxygen. So how come all the physical laws and parameters in the universe happen to have the values that allowed stars, planets and ultimately life to develop?

Some argue its just a lucky coincidence. Others say we shouldnt be surprised to see biofriendly physical laws they after all produced us, so what else would we see? Some theists, however, argue it points to the existence of a God creating favourable conditions.

But God isnt a valid scientific explanation. The theory of the multiverse, instead, solves the mystery because it allows different universes to have different physical laws. So its not surprising that we should happen to see ourselves in one of the few universes that could support life. Of course, you cant disprove the idea that a God may have created the multiverse.

This is all very hypothetical, and one of the biggest criticisms of theories of the multiverse is that because there seem to have been no interactions between our universe and other universes, then the notion of the multiverse cannot be directly tested.

Quantum weirdness

Now lets consider whether God can be in more than one place at the same time. Much of the science and technology we use in space science is based on the counter-intuitive theory of the tiny world of atoms and particles known as quantum mechanics.

The theory enables something called quantum entanglement: spookily connected particles. If two particles are entangled, you automatically manipulate its partner when you manipulate it, even if they are very far apart and without the two interacting. There are better descriptions of entanglement than the one I give here but this is simple enough that I can follow it.

Imagine a particle that decays into two sub-particles, A and B. The properties of the sub-particles must add up to the properties of the original particle this is the principle of conservation. For example, all particles have a quantum property called spin roughly, they move as if they were tiny compass needles. If the original particle has a spin of zero, one of the two sub-particles must have a positive spin and the other a negative spin, which means that each of A and B has a 50 percent chance of having a positive or a negative spin. (According to quantum mechanics, particles are by definition in a mix of different states until you actually measure them.)

The properties of A and B are not independent of each other they are entangled even if located in separate laboratories on separate planets. So if you measure the spin of A and you find it to be positive. Imagine a friend measured the spin of B at exactly the same time that you measured A. In order for the principle of conservation to work, she must find the spin of B to be negative.

But and this is where things become murky like sub-particle A, B had a 50:50 chance of being positive, so its spin state became negative at the time that the spin state of A was measured as positive. In other words, information about spin state was transferred between the two sub-particles instantly. Such transfer of quantum information apparently happens faster than the speed of light. Given that Einstein himself described quantum entanglement as spooky action at a distance, I think all of us can be forgiven for finding this a rather bizarre effect.

So there is something faster than the speed of light after all: quantum information. This doesnt prove or disprove God, but it can help us think of God in physical terms maybe as a shower of entangled particles, transferring quantum information back and forth, and so occupying many places at the same time? Even many universes at the same time?

Spooky action. Image via The Conversation/ Jurik Peter/Shutterstock

I have this image of God keeping galaxy-sized plates spinning while juggling planet-sized balls tossing bits of information from one teetering universe to another, to keep everything in motion. Fortunately, God can multitask keeping the fabric of space and time in operation. All that is required is a little faith.

Has this essay come close to answering the questions posed? I suspect not: if you believe in God (as I do), then the idea of God being bound by the laws of physics is nonsense, because God can do everything, even travel faster than light. If you dont believe in God, then the question is equally nonsensical, because there isnt a God and nothing can travel faster than light. Perhaps the question is really one for agnostics, who dont know whether there is a God.

This is indeed where science and religion differ. Science requires proof, religious belief requires faith. Scientists dont try to prove or disprove Gods existence because they know there isnt an experiment that can ever detect God. And if you believe in God, it doesnt matter what scientists discover about the universe any cosmos can be thought of as being consistent with God.

Our views of God, physics or anything else ultimately depends on perspective. But lets end with a quotation from a truly authoritative source. No, it isnt the bible. Nor is it a cosmology textbook. Its from Reaper Man by Terry Pratchett:

Light thinks it travels faster than anything but it is wrong. No matter how fast light travels, it finds the darkness has always got there first, and is waiting for it.

Monica Grady is a Professor of Planetary and Space Sciences atThe Open University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Subscribe to Moneycontrol Pro at 499 for the first year. Use code PRO499. Limited period offer. *T&C apply

Follow this link:

Can the laws of Physics help settle the debate over the existence of God? - Firstpost