Now, you've all heard the Grandfather Paradox, right?
If you haven't, it goes like this:

"Suppose you travelled back in time and killed your biological grandfather before he met your grandmother. Then you would never have been conceived, so you could not have travelled back in time after all. In that case, your grandfather would still be alive and you would have been conceived, allowing you to travel back in time and kill your grandfather, and so on."

Now this brings up an interesting question: What would happen if you actually did go back in time & killed your grandfather?
Would you die or would nothing happen?

depends on what quantum physics says. Reality is fluid in quantum physics. So must be time. Time must have a method of dealing with paradoxes, else the universe would not have lasted as long as it has. I'm of the mind that you could travel back in time and kill your grandfather and kill your line, but a branch of quantum reality would diverge where you still existed, and the line continued. The other theory would follow that you would not be allowed to kill your grandfather at all. That the past is locked and only the future is fluid. IF this is true, then we could see into the past but never interact. I still think it is possible and that time would heal itself, with consequences.

Jimmy

If you take into account alternate universe there is no paradox. Assume that you travel "back in time" but in reality (I use the term loosely) you merely jump to a parallel universe. You kill your alternate grandfather and the alternate you is never born. Could be that there are enough universes to account for every possible variation of every action in our universe. Thoughts?

I don't think you would cease to exist, you just wouldn't have been born, i don't hink you would "vanish". Events would be altered but i don't see how one could vanish.

But time travel paradoxes can get confusing.

Here is the problem with all this alternate/multiple universe theosophical pseudoscience.
One law of quantum mechanics states that the smaller the time interval, the smaller the probability for a quantum event. At the beginning of any event, the time interval is zero, so the probably of the quantum event initiating some alternate universe or new universe, whether at the Big Bang or attempting time travel is zero.


Now, here is where one of those rare situations arise where I will quote something metaphysical. Time is a river, and a man can never step into the same river twice.

LMAO

Josh1Wrote:
Here is the problem with all this alternate/multiple universe theosophical pseudoscience.

One law of quantum mechanics states that the smaller the time interval, the smaller the probability for a quantum event. At the beginning of any event, the time interval is zero, so the probably of the quantum event initiating some alternate universe or new universe, whether at the Big Bang or attempting time travel is zero.





Now, here is where one of those rare situations arise where I will quote something metaphysical. Time is a river, and a man can never step into the same river twice.



LMAO

Can probabilities ever be zero?

MatthewWrote:

[t]Josh1Wrote:
Here is the problem with all this alternate/multiple universe theosophical pseudoscience.

One law of quantum mechanics states that the smaller the time interval, the smaller the probability for a quantum event. At the beginning of any event, the time interval is zero, so the probably of the quantum event initiating some alternate universe or new universe, whether at the Big Bang or attempting time travel is zero.





Now, here is where one of those rare situations arise where I will quote something metaphysical. Time is a river, and a man can never step into the same river twice.



LMAO[/t]



Can probabilities ever be zero?

Can you mutliply anything and get zero?

In order for an event to have "begun" a period of time, no matter how small, must have past otherwise if it is zero nothing has happened, we are in the void of non-existence. I didn't mean to present my first opinion as a scientific hypothesis, more of a rambling of sorts. There still have to be small probabilities of alternate universes if something has happened under your explanation of quatum mechanic theory if I correctly understand it, if something has begun the time is not zero, it is zero before it has begun. You obviously lend no credence to superstring theory which requires a minimum of eleven dimensions/universes (not sure of the terminology).

MatthewWrote:
In order for an event to have "begun" a period of time, no matter how small, must have past otherwise if it is zero nothing has happened, we are in the void of non-existence. I didn't mean to present my first opinion as a scientific hypothesis, more of a rambling of sorts. There still have to be small probabilities of alternate universes if something has happened under your explanation of quatum mechanic theory if I correctly understand it, if something has begun the time is not zero, it is zero before it has begun. You obviously lend no credence to superstring theory which requires a minimum of eleven dimensions/universes (not sure of the terminology).

I was simplifying, more directed at the infinite universe models, but another quantum mechanical law stipulates that the bigger the mass brought into existence through a quantum fluctuation in the space-time fabric, the faster that mass must be returned to the space-time continuum. For something as massive as our observable universe, the return time would be briefer than 10 (-120) seconds. No one argues that the universe is so young.


You can see that the time paradox is more metaphysical musing than physics.

As for the "begun" reference, it may be a matter of perspective and definition, but the beginning time interval is zero. Only after it has begun has any time elapsed. Another perspective would be a time reversal, which , at some point, would have time "stopped", and again at zero.

MatthewWrote:
If you take into account alternate universe there is no paradox. Assume that you travel "back in time" but in reality (I use the term loosely) you merely jump to a parallel universe. You kill your alternate grandfather and the alternate you is never born. Could be that there are enough universes to account for every possible variation of every action in our universe. Thoughts?

i like it!
hawking delves into that a little in his writing.
one theory says if you were to be responsible for a change in the past that would eventually lead to a change of events preventing you from being able to travel to the exact same spot you are standing in, the you will be locked up in that universe with no way of returning to the previous.
which would SUCK, because in the original universe, you would be another missing person, leaving behind friends and family to ponder your disappearance, but in the new universe (and i may be off on this, but im pretty sure its accurate to the theory) there would be two of you existing in the same time. you and the you that lived in the universe prior to your entering it, which sucks for you because in this universe YOU are the imposter!
the bottom line: dont go onto other peoples universes!

you cant go back iand kill your grandfather simply because of the fact that the future depends directly on the preceding events. for example, if you eat an apple, you will feel full. why? because you ate the apple. the fullness comes after the eating. Simply put, the future you experience before you kill your grandfather happens as a result of ALL the occurances before this , INCLUDING your attempt to kill him. so by existing and being able to think about killing him, you have proven the fact that you will not kill him, since killing him would have effected your future already, and since you have already gotten to the point in which you live, you could not have killed your own grandfather.

Dude,

Having thought quite a bit about this ( I'd just like to add I'm only a fan of Theoretical Physics not a pro) but with the books I've read over the years I've come to my own conclusion - MAD as that sounds, but hey if people didn't have original ideas our race would never have learned anything...

Quantum physics basically ALL boils down to the particle version of the Young's slits experiment. The Schrodinger problem of trying to predict the 'future'.

The supposedly unexplainable 'Grandfather' time problem which would be a paradox I don't think is in any way a problem.


It depends on how we think about 'Time'. I use the word time in ' ' and will do my best to explain why.

Richard Feynman, one of my major heroes put is bloddy well with his Q.E.D explanation and his 'sum-over-histories'

However: THE EASY EXPLANATION

As long as a particle does not have to be 'measured' or be 'realised' in the eternally moving here-and-now 'exact' moment in time, it exists in a Super-State.

Einstein questioned "If I travelled at the speed of light and held a mirror up to my face, would I see my reflection?" After years of deliberation he decided YES, this is fundamental to relativity. So with Einstein travelling at the speed of light, another light ray (photon) would also travel at the 'speed-of-light' leaving the surface of the mirror as another order of magnitude. The BIG thing here Einstein was saying is TIME.

I have come to understand there is an infinite sequence in orders of magnitude of the speed-of-light, none any faster or slower than the other (depending on the medium it is travelling through), but the timeframe in which they exist allows this to be so.

To Feynmans sum-over-histories explanation I would like to add my own 'the sum-over-futures' concept . The resulting location / direction of a photon in the here and now is affected by it's ENTIRE history and its ENTIRE future.

Could talk, and would love to talk about this for years, but in a nutshell:

It is not possible to create a Paradox, because the sum-over-futures affects our present and past as well.

These are my ideas and not 'the official line'

I recomend you read:

The quantum brain

any Feynman on Q.E.D


P.S.

Would love to hear what others think about this concept

I recon you would come back, and everyone would say, "who the fuck are you?"

You are all idiots. "The Universe you just came back in time from would collapse and you would just go back and kill your grandfather. The Universe between the point your grandfather died and the point you went back in time would be a tangent Universe. Jesus, everyone knows we should get all our scientific knowledge from Donnie Darko." - Stephen Hawking, A Brief History Of Time

damn you all!!!!!! you wrote all my therories before i had a chance to join this group! anywho, the way i see it, the only way to go back in time, is through a wormhole (isn't it?), and the odds of a wormhole actually coming into existance are so small that it's possible it hasn't happened yet. which is a scary thought, because i think the most probable outcome of a paradox is the collapse of the universe. i also think it would make a sound something like "bzzzt!"

if i were you, i'd make sure you got your shit in order, our days could be seriously numbered man.