Phuck Yeah Physics
Because chemists can't top the hydrogen bomb.

Because chemists can't top the hydrogen bomb.
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unknownskywalker: Quantum Time Machine Solves Grandfather Paradox A new kind of time travel based on quantum teleportation gets around the paradoxes that have plagued other time machines. Of all the weird consequences of quantum mechanics, one of the strangest is the notion of postselection: the ability to trigger a computation that automatically disregards certain results. Here’s an example: suppose you have a long expression in which there are a frighteningly large number of variables. The question you want answering is which combination of variables makes the expression logically true. And the conventional way to solve it is by brute force: try every combination of variable until you find one that works. Postselection makes the solution easy to find by simply allowing the variables to take any value at random and then postselect on the condition that the answer must be true. This is controversial because it leads to all kinds of fantastical predictions about the power of quantum computers. Nobody is quite sure if these kinds of computations are possible or how to achieve them but quantum mechanics seems to allow them. MIT researchers say that if you build a time machine combinig postselection with another strange quantum such as teleportation, this uses the phenomenon of entanglement to reproduce in one point in space a quantum state that previously existed at another point in space. The idea is to use postselection to make this process happen in reverse, ensuring that only a certain type of state can be teleported. This immediately places a limit on the state the original particle must have been in before it was teleported. In effect, the state of this particle has travelled back in time. What’s amazing about this time machine is that it is not plagued by the usual paradoxes of time travel, such as the grandfather paradox, in which a particle travels back in time and some how prevents itself from existing in the first place. This time machine gets around this because of the probabilistic nature of quantum mechanics: anything that this time machine allows can also happen with finite probability anyway, thanks to these probabilistic laws. Another interesting feature of this machine is that it does not require any of the distortions of spacetime that traditional time machines rely on. In these, the fabric of spacetime has to be ruthlessly twisted in a way that allows the time travel to occur. These conditions may exist in the universe’s extreme environments such as inside black holes but probably not anywhere else. Postselection can only occur if quantum mechanics is nonlinear, something that seems possible in theory but has never been observed in practice. All the evidence so far is that quantum mechanics is linear. In fact some theorists propose that the seemingly impossible things that postselection allows is a kind of proof that quantum mechanics must be linear. However, if nonlinear behaviour is allowed, time travel will be possible wherever it takes place. It is possible for particles (and, in principle, people) to tunnel from the future to the past. Source: Technology Review | The paper of this research is available via arXiv.org

unknownskywalker:

Quantum Time Machine Solves Grandfather Paradox

A new kind of time travel based on quantum teleportation gets around the paradoxes that have plagued other time machines. Of all the weird consequences of quantum mechanics, one of the strangest is the notion of postselection: the ability to trigger a computation that automatically disregards certain results.

Here’s an example: suppose you have a long expression in which there are a frighteningly large number of variables. The question you want answering is which combination of variables makes the expression logically true. And the conventional way to solve it is by brute force: try every combination of variable until you find one that works.

Postselection makes the solution easy to find by simply allowing the variables to take any value at random and then postselect on the condition that the answer must be true. This is controversial because it leads to all kinds of fantastical predictions about the power of quantum computers. Nobody is quite sure if these kinds of computations are possible or how to achieve them but quantum mechanics seems to allow them.

MIT researchers say that if you build a time machine combinig postselection with another strange quantum such as teleportation, this uses the phenomenon of entanglement to reproduce in one point in space a quantum state that previously existed at another point in space.

The idea is to use postselection to make this process happen in reverse, ensuring that only a certain type of state can be teleported. This immediately places a limit on the state the original particle must have been in before it was teleported. In effect, the state of this particle has travelled back in time.

What’s amazing about this time machine is that it is not plagued by the usual paradoxes of time travel, such as the grandfather paradox, in which a particle travels back in time and some how prevents itself from existing in the first place. This time machine gets around this because of the probabilistic nature of quantum mechanics: anything that this time machine allows can also happen with finite probability anyway, thanks to these probabilistic laws.

Another interesting feature of this machine is that it does not require any of the distortions of spacetime that traditional time machines rely on. In these, the fabric of spacetime has to be ruthlessly twisted in a way that allows the time travel to occur. These conditions may exist in the universe’s extreme environments such as inside black holes but probably not anywhere else.

Postselection can only occur if quantum mechanics is nonlinear, something that seems possible in theory but has never been observed in practice. All the evidence so far is that quantum mechanics is linear. In fact some theorists propose that the seemingly impossible things that postselection allows is a kind of proof that quantum mechanics must be linear.

However, if nonlinear behaviour is allowed, time travel will be possible wherever it takes place. It is possible for particles (and, in principle, people) to tunnel from the future to the past.

Source: Technology Review | The paper of this research is available via arXiv.org

invaderxan: I hope reality hasn’t scared you too much. If it has, then don’t worry. Reality might not last. Despite what you might think, vacuum doesn’t imply empty. The vacuum of space actually contains vacuum energy. Energy which, it could be said, is intrinsic to the fabric of spacetime itself in our Universe. Stephen Hawking was the fist to realise that the vacuum in our universe may not be at the lowest energy state it could be.  If this is true, and our Universe contains a “false vacuum”, then quantum mechanics says it might tunnel into a lower energy state. Causing a vacuum metastability event, this could either do absolutely nothing, or it could fundamentally alter the whole Universe in the blink of an eye. There’s even a chance that it might cause the laws of physics to drastically change. Quantum mechanics works by probability, so if we really do live in a metastable vacuum, then all structures in the Universe could be instantaneously destroyed at any time. Without warning. .̣̟͠.̺̮̰͉̲̝̘̆ͮ́͆̆̚.͓̺͗̉͆͡ .̢̛̪̜̱͎̗̩̦̜͙̣͎̜͓̖̬͈̙̪͋ͥ͋͊̕͟͠.̞̲̣̻̫͗͊͛̈́ͬ͂͟.̖͙͇̲̞̉̆͆͒̆̿́́̕͟͢ H̨̰̙͙̖̣̙͕ͥ̓̓̅̐̋̓̇̀A̙̯̬͋ͩͨ͜V̯̺̠̭̳͙̥͉̎ͮ̚͜Ȅ̙̜̟ ̅͊͑ͯ͊̽̇́͏͈̺̗͖̭͓̀P̢̛̗̤̓ͧ͛͑͗̚̚L͚̹̟̠͈ͤ̊ͅĚ̦̮͚̾̏A̶̘̹̼̜̜̜̿̓ͅŚ̶̱ͧͅA̮̹̰̮̣̮ͣ͂̓͒ͧ̚͡ͅN̶̈́ͭ͏̨͇͙͕͉̬̪̪ͅT̤̥̪̤̄͆͛̀ ̢̻̬̥̗̱͇ͧ͌̿́D̺ͦ̿̒ͦͭ̃̽R̯̹͇̥̗̦ͬ̓̐ͩ͆E͎̖̳̞̋̄̍͆͐Ą̖̥̯̖̪̳̃ͨ̓̈ͬM̶̛̪͇̮̬͕̲͎͔̩̍ͦ̐Ṡ̋̔ͬ͌̉̐̍̾͏̞̞̼̠̳.̒͂̍ͦ͏͙̗̳͚̥͍.̩͈̹͙̮͎̔͌̒.̨̹̈̅͌͌ͯͩ͢.̛̹ͪ̾.͊ͩ͡.͕̟

invaderxan:

I hope reality hasn’t scared you too much. If it has, then don’t worry. Reality might not last.

Despite what you might think, vacuum doesn’t imply empty. The vacuum of space actually contains vacuum energy. Energy which, it could be said, is intrinsic to the fabric of spacetime itself in our Universe.

Stephen Hawking was the fist to realise that the vacuum in our universe may not be at the lowest energy state it could be. 

If this is true, and our Universe contains a “false vacuum”, then quantum mechanics says it might tunnel into a lower energy state. Causing a vacuum metastability event, this could either do absolutely nothing, or it could fundamentally alter the whole Universe in the blink of an eye. There’s even a chance that it might cause the laws of physics to drastically change.

Quantum mechanics works by probability, so if we really do live in a metastable vacuum, then all structures in the Universe could be instantaneously destroyed at any time. Without warning.

.̣̟͠.̺̮̰͉̲̝̘̆ͮ́͆̆̚.͓̺͗̉͆͡

.̢̛̪̜̱͎̗̩̦̜͙̣͎̜͓̖̬͈̙̪͋ͥ͋͊̕͟͠.̞̲̣̻̫͗͊͛̈́ͬ͂͟.̖͙͇̲̞̉̆͆͒̆̿́́̕͟͢

H̨̰̙͙̖̣̙͕ͥ̓̓̅̐̋̓̇̀A̙̯̬͋ͩͨ͜V̯̺̠̭̳͙̥͉̎ͮ̚͜Ȅ̙̜̟ ̅͊͑ͯ͊̽̇́͏͈̺̗͖̭͓̀P̢̛̗̤̓ͧ͛͑͗̚̚L͚̹̟̠͈ͤ̊ͅĚ̦̮͚̾̏A̶̘̹̼̜̜̜̿̓ͅŚ̶̱ͧͅA̮̹̰̮̣̮ͣ͂̓͒ͧ̚͡ͅN̶̈́ͭ͏̨͇͙͕͉̬̪̪ͅT̤̥̪̤̄͆͛̀ ̢̻̬̥̗̱͇ͧ͌̿́D̺ͦ̿̒ͦͭ̃̽R̯̹͇̥̗̦ͬ̓̐ͩ͆E͎̖̳̞̋̄̍͆͐Ą̖̥̯̖̪̳̃ͨ̓̈ͬM̶̛̪͇̮̬͕̲͎͔̩̍ͦ̐Ṡ̋̔ͬ͌̉̐̍̾͏̞̞̼̠̳.̒͂̍ͦ͏͙̗̳͚̥͍.̩͈̹͙̮͎̔͌̒.̨̹̈̅͌͌ͯͩ͢.̛̹ͪ̾.͊ͩ͡.͕̟

clearscience: But what is a quantum, and what does it have to do with quantum mechanics? A quantum is any quality that must occur in discrete, non-continuous increments. Consider the two rows of color shown above. In the top one, light blue transitions to dark blue continuously, moving through all the in-between values on the way. If you characterized the shades of blue with numbers, you might say the color of that bar could have a blue of 1, a blue of 1.001, a blue of 1.002, all the way up to a blue of 5. On the bottom, however, the blue is quantized, occurring in only 5 values: 1, 2, 3, 4, or 5. That’s it. There can be no in-between values. What Planck discovered about light was that its energy was like the blue in the bottom row: it could only have distinct values, and going from one to the other meant adding another photon. (Photons emitted by the metal in the photo are making it glow.) So what does this have to do with mechanics? Perhaps light is not the only thing that has quantized energy. In fact this is the case: the energy levels of the particles that make up atoms, and therefore everything, also have discrete quanta.

clearscience:

But what is a quantum, and what does it have to do with quantum mechanics? A quantum is any quality that must occur in discrete, non-continuous increments. Consider the two rows of color shown above. In the top one, light blue transitions to dark blue continuously, moving through all the in-between values on the way. If you characterized the shades of blue with numbers, you might say the color of that bar could have a blue of 1, a blue of 1.001, a blue of 1.002, all the way up to a blue of 5.

On the bottom, however, the blue is quantized, occurring in only 5 values: 1, 2, 3, 4, or 5. That’s it. There can be no in-between values. What Planck discovered about light was that its energy was like the blue in the bottom row: it could only have distinct values, and going from one to the other meant adding another photon. (Photons emitted by the metal in the photo are making it glow.)

So what does this have to do with mechanics? Perhaps light is not the only thing that has quantized energy. In fact this is the case: the energy levels of the particles that make up atoms, and therefore everything, also have discrete quanta.

Testing the Hypothesis of a Holographic Universe at Fermilab

The holographic principle of the universe has been a popular theory among crazies and string theorists for years.

In a larger and more speculative sense, the theory suggests that the entire universe can be seen as a two-dimensional information structure “painted” on the cosmological horizon, such that the three dimensions we observe are only an effective description at macroscopic scales and at low energies. Cosmological holography has not been made mathematically precise, partly because the cosmological horizon has a finite area and grows with time.[2][3]

Take a look at the back of a credit card. You can see the metallic two-dimensional sticker on the back, right? When you tilt it back and forth, the image on the sticker appears to be three-dimensional as light reflects off of it in the changing light. The holographic prinicple of the universe says that this is how the universe behaves: the entire universe is two-dimensional and we only perceive it to be three dimensional because of a quirk of light, but also that we’re incapable of recognizing the holography of the universe as a result of the precision of the hologram (much like a really convincing 3D movie that you’ve been watching your whole life).

The idea that spacetime may not be entirely smooth – like a digital image that becomes increasingly pixelated as you zoom in – had been previously proposed by Stephen Hawking and others. Possible evidence for this model appeared last year in the unaccountable “noise” plaguing the GEO600 experiment in Germany, which searches for gravitational waves from black holes. To Hogan, the jitteriness suggested that the experiment had stumbled upon the lower limit of the spacetime pixels’ resolution.

The universe is probably not smooth. This has been theorized since the days of Max Planck around the turn of the last century and today the supposed graininess of the universe is relatively well-accepted, as far as new and crazy/mind-blowing/debilitating theories go.

Proponents of this theory have long been resigned to the ranks of stoner philosophy majors going on about how the universe is totally flat, man, totally. In the background, though, theorists have been refining the theory and now it’s time for them to shine.

“So we want to build a machine which will be the most sensitive measurement ever made of spacetime itself,” says Hogan. “That’s the holometer.”

…

The holometer’s precision means that it doesn’t have to be large; at 40 meters in length, it is only one hundredth of the size of current interferometers, which measure gravitational waves from black holes and supernovas. Yet because the spacetime frequencies it measures are so rapid, it will be more precise over very short time intervals by seven orders of magnitude than any atomic clock in existence.

The results from this experiment will likely be a hot topic of debate for a long time, but if a definitive answer is shown then it could revolutionize not only the field of quantum mechanics, but physics as a whole.

Quantum Mechanics!

If you liked the post about quantum tunnelling, check out the premier QM blog on tumblr by clicking the above link. It’s run by the crazy smart entangled and is all QM all the time. Go go go!