Star Trek

Of course, we're assuming that it is possible. I believe that 1 and 3 are most plausible, although 1 is kind of depressing.

Quote (Giantevilhead @ Nov. 22 2004, 9:28 pm)

Of course, we're assuming that it is possible. I believe that 1 and 3 are most plausible, although 1 is kind of depressing.

Actually I believe all the choices are possibles. We do have a hint how  retrograde time travel would works.

Dr john Wheeler created an experiment to test whether one could effect the choice of which slit a single photon travel thru after the Photon had already pass thru the slit. This experiment called the Delay choice experiment showed that one could actually effect the path a photon could take in the past.

Another verison of the Test called the Quantum eraser actually let scientist go back and erase the choice.

We can actually alter the past and alter it again for subatomic particles.

This may explain why history is so vague at time, with observers and written account sometime disagree on events. Maybe some one or something is altering the past constantly.

for more on Quantum eraser experiment, see :http://www.npl.washington.edu/AV/altvw90.html

Depressingly, I have to agree with the first method. Time is fixed. Causality makes sure that there is only one possible time line that progresses in only one way - no way to deviate.
If you go back in time, you're fullfilling something that had already been predestined to happen, therefore already happened before you went back.

Alternatively, option 3 could be possible, but the idea of multiple Universes goes against the causality idea... although it does make a certain kind of sense in a way. However, it also means that cool time loops are impossible.

Quote (Start_Wreck @ Nov. 23 2004, 1:39 am)

Depressingly, I have to agree with the first method. Time is fixed. Causality makes sure that there is only one possible time line that progresses in only one way - no way to deviate. If you go back in time, you're fullfilling something that had already been predestined to happen, therefore already happened before you went back. Alternatively, option 3 could be possible, but the idea of multiple Universes goes against the causality idea... although it does make a certain kind of sense in a way. However, it also means that cool time loops are impossible.

But the Quantum eraser experiment prove that wrong. Not only is the past fluid but is depend on the actions of the present.

we can expand the experiment and use a photon from a quasar and gravity lens of  galaxy allowing us to effect the photon billions of years in the past.

This show one form of paradox. Wormholes would us allows to form region of space that would behave as alternate time lines or loops.

Causality is not a fix feature of the universe, as work on Quantum gravity shows. Each local potion of space is connected to it self, but is disconnected to distant potion of space time.

Relativity show that, two observer in different inertial frames can view a single event with a completel different order of actions.

The problem is that Causality is concept of the human mind, but to quantum physics time is symmetrical and past and future are accessable.

Our present ideas on how time behave is outmode, common logic doesnot apply to time travel or to actual properties of time,  future work on string and Quantum gravity will most likely show that time behave in a manner completely different from our view of it.

Quote (lanceromega @ Nov. 23 2004, 2:58 am)

But the Quantum eraser experiment prove that wrong. Not only is the past fluid but is depend on the actions of the present. we can expand the experiment and use a photon from a quasar and gravity lens of galaxy allowing us to effect the photon billions of years in the past.

Hmm, I found that a bit vague, to be honest.

Could you explain the experiment in more detail? How exactly was the photon affected in the past, and how does one observe it 'changing'?

Quote (Start_Wreck @ Nov. 23 2004, 4:11 am)

Quote (lanceromega @ Nov. 23 2004, 2:58 am) But the Quantum eraser experiment prove that wrong. Not only is the past fluid but is depend on the actions of the present. we can expand the experiment and use a photon from a quasar and gravity lens of  galaxy allowing us to effect the photon billions of years in the past. Hmm, I found that a bit vague, to be honest. Could you explain the experiment in more detail? How exactly was the photon affected in the past, and how does one observe it 'changing'?

In order to understand the Eraser experiment we have to go into the basic double slit experiment,

Basically a wave going thru two slits will interfer with each other creating alternating bands of light and dark. A stream of particles will create two bright spots, where the particles strike.

Cover one slit and waves will still interact with them self giving a alter diffusion pattern, while particle will create a single bright spot ( thru the slit it travel thru).

Now a photon show both behavior, cover one slit and it create a single bright spot, uncover the slit and it will interact with is self like a wave.

Physicists attempt to cheat by placing a photon detector at both slits, hoping to catch it going thru both slits, but it don't it simply register on a single detector, acting like a particle.

Wheeler wanted to cheat, he wanted to place the detector in place after the photon past thru the slit to see if the photon could detect that it should be behaving like a particle, and it does... Some how a path can be alter after a single slit have been covered after the Photon had already travel thru it!!!

In the Quantum eraser experiment we add an additional twist, we split the laser beam, creating two entangle beams, send them down seperate paths and seperate test rigs. We then can alter one set of Paths to create a block slit. and undo the block by altering the slit or detector on the other, rewriting a change to the path created in the path from the present, not just once but twice.

This experiment show that the history of a particle can actually be alter and alter over again. Baiscally we can rewrite history!!!

Okay then.
Is there a website I can go to to look at this stuff?

Quote (SuperBlob @ Nov. 24 2004, 2:04 am)

If you read the original link, the Gravity lens is behaving just like the beam splitter, by conducting the experiment you can actually determine which path it take around the imposing galaxy.

The whole delay choice experiment allow someone in the present by deciding whether to test for wave or particle like behavior to somhow communicate to the photon in the past to determine the course it takes.

The delay can be in millisecond or in billion of years. Just as Quantum teleportation attacks locality and Causality due to distant, The Delay choice assault it over time.

As for your statement about My opinion as being Fallacies, I find it amazing that you donot provide any support for your view point. I at the least has the support of host of Quantum Physicist and several experiments that show the strange nature of time as revealed by the "Delay choice and Quantum Eraser experiments...

Quote (Start_Wreck @ Nov. 24 2004, 1:47 am)

Okay then. Is there a website I can go to to look at this stuff?

Here is a site that explains the Delay choice experiment in detail, It should not be that hard to follow, plus it has a link to Eraser Experiment.

http://www.bottomlayer.com/bottom/basic_delayed_choice.htm

Now this show that at least Quantum Physics allow you to alter the past, and it not Fix. There is only mathematical prove for Time loop, since to create these loop require wormholes and Space craft able to travel at Relativitic Velocity, but already we have two possible way that a time travel can interact with the past.

I'm not trying to say you're wrong, it just makes no sense(the logic) behind time traveling into the past.

Quote (SuperBlob @ Nov. 25 2004, 1:58 am)

I'm not trying to say you're wrong, it just makes no sense(the logic) behind time traveling into the past.

Problem is that what we call logic is not the logic of the universe. Quantum mechanics follows it own logic which is so different from the human logic, that even Albert Einstein, one of its founding fathers, could not come to grips with it.

He spent the last years of his life, coming up with experiments to disprove it. EPR which is known as Quantum teleportation was his brain child and was an attempt to disprove the Uncertainty principle..As it stand it show that Quantum Physics was weirder than what he believed and one of the possible explaination of reality behind QM was either Causatly or Locality were not Valid concepts!!!

Even Relativity show that how we perceive Causalty is mutable. A chain of events can be seen as having a different order of Sequence to different observers, this called the Relavitity of Simultaneity, show how cause and effect can be altered to observators in different inertial frames.

Quantum Physics has Particle that can spring out of nothingness at random (called virtual particles), the limitation on lenght of their existant is dependent on the uncertainty of energy that the particle possess, which determines when they must once again return to nothingness.

The Limit on all paradoxes may be one of energy, Physicist that study time travel call this Genies. A small paradox require an inlaid of small amount of energy a larger paradox like creating a time clone of a person would require an massive outlaid of energy making it unlikely, but with a creation of a stable wormhole large amounts of energy become available ( The negative energy use to support a worm hole would has the potential of creating a new universe!! So Close time loop can occur, due to fact that paradox itself creates a self contain universe...

As for undoing a person or altering him, all matter is mutable it can be created or alter and this is  done all the time ( look at he example of particles springing out of the nothingness and returning). The same Delay choice experiment can be done with Electrons, protons and neutrons (Slow ones) and the history of their moment thru the slit can be alter just as easily. We are nothing more than a collection of particles so if a single particle past can be altered so can our. With the delay choice experiment the change happens in our past, not an alternate time line (The Quantum erase experiment prove this), no new universe spring up, and the Paradox is easily observed.

You right, time travel would not make sense ( that why Einstein maintain that it impossible to go faster than light, this would throw cause and effect out the window), but that is property of time travel. The logic that Time travel demand would be one vastly different from the non time traveller reference frame, but to one involved in the time traveling it would make perfect sense as long as he or she has the energy to pay for it.

Killing you grandfather requires transient thru a galaxy size blackhole (use a worm hole and you may create a close time loop) and the ablities to escape its gravity. One you do that ( Fairly easy,lol) you need to travel FTL to get to earth in time to commit the murder before your father is born. All of this require the energy to create whole universes, so feel free to try and remember donot sleep with  your grandmother or all of you efforts could be for naught...

Quote (lanceromega @ Nov. 24 2004, 12:00 pm)

Here is a site that explains the Delay choice experiment in detail, It should not be that hard to follow, plus it has a link to Eraser Experiment. http://www.bottomlayer.com/bottom/basic_delayed_choice.htm

Thanks for that!

The Delay Choice thing makes sense to me; I followed that okay. The Eraser Experiment seems completely lost on me, though. Either it seems to be logically flawed or I'm simply not 'getting' it (I suspect the latter). However, it seems to rest on some kind of magical 50/50 probability issue that I'm not too comfortable with, as it's not very precise about what causes it and why.

Let me try to put some of thoughts into better words here, as this is still swimming around my (already tired) head this morning...

Regarding the Delay Choice experiment: A photon is sent towards two slits (A and B), with the possibility that it will either have a wave formation (and therefore travel through both slits) or a particle formation (and therefore travel through only one slit [A or B]). I presume there must be something that determines whether it is A or B, but I guess it is largely irrelevant for this discussion. The real question is what causes it to be either a wave or a particle, and that's what we will find out at the end.

So, the photon has travelled through a slit, or both slits. We don't know yet, because we can't detect it at the moment. In order for it to have passed through both slits, it needs to be a wave pattern. In order for it to pass through only one slit, it needs to be a particle pattern. So now comes the part where we detect that...

We set up a screen at the far end which can detect the light hitting it. All experiments show a wave-like pattern which proves that the light must have travelled through both slits in the form of a wave. Every experiment that uses a screen to detect the photons will give this same result.

Now comes the clever part: It is possible to very quickly remove the screen. So quickly, in fact, that it can be removed faster than the light can reach it after it's already passed through the slits (in order for this to be reasonably possible, the screen would have to be a very long way from the slits -- but it is physically possible to do).
Behind the screen are two telescopic devices each trained onto one of the slits. When looking through these devices you can see a flash of light to indicate that the photon has travelled through the slit that the telescope is looking at. It will either be one or the other... but it is never both.

Now, this is interesting, because if the light doesn't appear in both devices, how can it be a wave pattern? It can't; it has to be a particle pattern and therefore has only travelled through one slit.

So, to clarify: When we observe the results on the screen, we see that the light travelled through both slits. When we observe the results through the telescope, we see the light has travelled through only one slit.

Since we can make that choice after the light has already passed the slits, we would assume that the answer already exists and we just don't know it yet, but it would appear that this isn't the case, because it would otherwise be a complete coincidence every time. What we discover is that our choice whether or not to move the screen or not move the screen is what causes a result that has already happened. Essentially, an action in the present affects something that happened in the past.


How bizarre!


Have I understood it properly?


If so, here are some problems and possibilities:

1. We're assuming that the photon cannot be both a wave and a particle. Is it possible that it is both? Will the screen detect the photon as a particle or is it only designed to detect it as a wave?
Let's imagine (and feel free to laugh at my probably totally incorrect physics, here) that the light travels from the source in both a wave and particle pattern. Putting a screen there will detect the wave distribution pattern but won't detect the particle pattern (which is there also but isn't detectable).
Not having the screen there will show the particle pattern but not the wave pattern (which is still there but isn't detectable). I don't know how exactly these things are detected, but it seems strange to me that the sreen will only detect the wave and the telescopes will only detect the particles.
Even if (and I'm assuming it can) the telescopes could detect the wave (ie. light passes through both slits and into both telescopes) we couldn't say that we chose it unless we know for sure that the particles never hit the screen. Do we know that, or do we simply know that they aren't detectable on the screen? Or are they detectable on the screen but it just never happens?

A little help here, please!!


2. We're assuming (perhaps -- again, feel free to laugh uncontrollably at my total lack of physics understanding) that the photon 'travel' in a traditional sense in a forwards motion. What if it doesn't? What if photons 'travel' by being everywhere at once, and will only be at a later position if it has already been decided (the instant it leaves) that it can reach the place it's going to? We know that time dilation would make the passage of time to any photon instantaneous and infinite. ie. It would know, in its time, whether or not the screen is there before it has left to choose a slit by our time reference. This is getting tricky for me now... -- What if the reason the photon is detected one way or the other depending on our method, is because the photon knows that method before we've done it, because by its own time frame, it has already happened. Wouldn't it be similar to the reason why electricity won't travel through a circuit unless that circuit is complete? Or a similar reason at least?
Or have I inadvertantly explained the exact same result as the experiment originally suggested albeit from the perspective of the photon instead?

Agh, my head hurts!

Right, I'll tackle the Eraser thing later. I need to lie down.

Quote (Start_Wreck @ Nov. 25 2004, 3:35 am)

Quote (lanceromega @ Nov. 24 2004, 12:00 pm) Here is a site that explains the Delay choice experiment in detail, It should not be that hard to follow, plus it has a link to Eraser Experiment. http://www.bottomlayer.com/bottom/basic_delayed_choice.htm Thanks for that! The Delay Choice thing makes sense to me; I followed that okay. The Eraser Experiment seems completely lost on me, though. Either it seems to be logically flawed or I'm simply not 'getting' it (I suspect the latter). However, it seems to rest on some kind of magical 50/50 probability issue that I'm not too comfortable with, as it's not very precise about what causes it and why. Let me try to put some of thoughts into better words here, as this is still swimming around my (already tired) head this morning... Regarding the Delay Choice experiment: A photon is sent towards two slits (A and B), with the possibility that it will either have a wave formation (and therefore travel through both slits) or a particle formation (and therefore travel through only one slit [A or B]). I presume there must be something that determines whether it is A or B, but I guess it is largely irrelevant for this discussion. The real question is what causes it to be either a wave or a particle, and that's what we will find out at the end. So, the photon has travelled through a slit, or both slits. We don't know yet, because we can't detect it at the moment. In order for it to have passed through both slits, it needs to be a wave pattern. In order for it to pass through only one slit, it needs to be a particle pattern. So now comes the part where we detect that... We set up a screen at the far end which can detect the light hitting it. All experiments show a wave-like pattern which proves that the light must have travelled through both slits in the form of a wave. Every experiment that uses a screen to detect the photons will give this same result. Now comes the clever part: It is possible to very quickly remove the screen. So quickly, in fact, that it can be removed faster than the light can reach it after it's already passed through the slits (in order for this to be reasonably possible, the screen would have to be a very long way from the slits -- but it is physically possible to do). Behind the screen are two telescopic devices each trained onto one of the slits. When looking through these devices you can see a flash of light to indicate that the photon has travelled through the slit that the telescope is looking at. It will either be one or the other... but it is never both. Now, this is interesting, because if the light doesn't appear in both devices, how can it be a wave pattern? It can't; it has to be a particle pattern and therefore has only travelled through one slit. So, to clarify: When we observe the results on the screen, we see that the light travelled through both slits. When we observe the results through the telescope, we see the light has travelled through only one slit. Since we can make that choice after the light has already passed the slits, we would assume that the answer already exists and we just don't know it yet, but it would appear that this isn't the case, because it would otherwise be a complete coincidence every time. What we discover is that our choice whether or not to move the screen or not move the screen is what causes a result that has already happened. Essentially, an action in the present affects something that happened in the past. How bizarre! Have I understood it properly? If so, here are some problems and possibilities: 1. We're assuming that the photon cannot be both a wave and a particle. Is it possible that it is both? Will the screen detect the photon as a particle or is it only designed to detect it as a wave? Let's imagine (and feel free to laugh at my probably totally incorrect physics, here) that the light travels from the source in both a wave and particle pattern. Putting a screen there will detect the wave distribution pattern but won't detect the particle pattern (which is there also but isn't detectable). Not having the screen there will show the particle pattern but not the wave pattern (which is still there but isn't detectable). I don't know how exactly these things are detected, but it seems strange to me that the sreen will only detect the wave and the telescopes will only detect the particles. Even if (and I'm assuming it can) the telescopes could detect the wave (ie. light passes through both slits and into both telescopes) we couldn't say that we chose it unless we know for sure that the particles never hit the screen. Do we know that, or do we simply know that they aren't detectable on the screen? Or are they detectable on the screen but it just never happens? A little help here, please!! 2. We're assuming (perhaps -- again, feel free to laugh uncontrollably at my total lack of physics understanding) that the photon 'travel' in a traditional sense in a forwards motion. What if it doesn't? What if photons 'travel' by being everywhere at once, and will only be at a later position if it has already been decided (the instant it leaves) that it can reach the place it's going to? We know that time dilation would make the passage of time to any photon instantaneous and infinite. ie. It would know, in its time, whether or not the screen is there before it has left to choose a slit by our time reference. This is getting tricky for me now... -- What if the reason the photon is detected one way or the other depending on our method, is because the photon knows that method before we've done it, because by its own time frame, it has already happened. Wouldn't it be similar to the reason why electricity won't travel through a circuit unless that circuit is complete? Or a similar reason at least? Or have I inadvertantly explained the exact same result as the experiment originally suggested albeit from the perspective of the photon instead? Agh, my head hurts! Right, I'll tackle the Eraser thing later. I need to lie down.

Welcome to existant The Eraser experiment just add an additional level of weirdness , so good luck, cause the the eraser allow us to alternate the result after the photon is detect!!

It no small wonder that Einstein felt that something was missing from QM.

As it stand there is a new factor in all this, a Physicist has figure out a way to detect (using the double slit experiment) a photon  behaving as both a particle and a wave, and this help to reinforce an interperation of QM called the The Transactional Interpretation of Quantum Mechanics which has the photon communicating with it self with backward time traveling signals from the particle own future....

If you like check out the following link for More on TIOQ, it will give you less headaches than Delay choice, but it may keep you up at night.. :

http://mist.npl.washington.edu/TI/

Quote (lanceromega @ Nov. 22 2004, 10:06 pm)

Another verison of the Test called the Quantum eraser actually let scientist go back and erase the choice. We can actually alter the past and alter it again for subatomic particles. for more on Quantum eraser experiment, see :http://www.npl.washington.edu/AV/altvw90.html

Yes I remember the claim of this experiment way back in the eighties.

You can measure photons as particle or waves and the results will be different; but the difference is in the apparatus, not in a 'changed nature' of the photon. Photons have dual nature, being both particles and waves at the same time; that's what makes them so hard to understand.

Quote

Only after the photon has passed the slit plane does the experimenter decide whether to measure its one slit position (D down) or its two slit momentum (D up). Delayed-choice experiments of this type have actually been performed, and the interference pattern detected when D is up is not affected by the delayed choice. Somehow the photon can retroactively arrange to go through one slit or two depending on which measurement is ultimately made.

I'm not convinced this is a real experiment. Here's why.

The theory goes (this is the original one from the 80's) that particles would be 'gravitationally lensed' (particles have mass, affected by gravity), whereas waves wouldn't be (waves being massless). Actually, a telescope lens also relies on the wave nature of light to make the 'lensing' effect. If the results of this experiment were true, using a particle detector (your eye, a CCD, etc.) on a telescope would then force the photons into a particle state, and negate the ability of the lens to focus light.

As far as I've seen, whatever method astronomers use to detect photons coming through a gravitational lens (spectoscopically [waves] or CCD imaging [particles] ), the lens effect is always there. The nature of the photon does not change based on the method of detection.

Science is filled with people 'fudging' experiments to make them say what they want. I'll believe in reality, thanks.