# Temporal Dilemma

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##### Guest
Let us assume that time travel is in fact possible. Let us also assume that time is not as fragile as we perceive and that the problem of paradoxes can be nicely swept under the rug through either the use of closed time loops("self-fulfilling histories") or alternate timelines.
A problem does arise still. The problem being the conservation of matter/energy which states that matter/energy can not be created or destroyed but can only change form. An individual travelling backwards from one time period into another would in effect be increasing the energy(matter) of the universe. Although, I suppose one way to get around this is to invoke a principle of quantum physics (the Heisenberg Uncertainity Principle). This principle states that there is a minimum uncertainity with regards to measurements of energy(dE) and time(dt),dEdt ] h. This minimum uncertainity is known as the quantum of action or simply Planck's constant. Basically, what this says is: it is possible to "borrow" energy from the vacuum(E=0) (i.e. go into energy debt) so long as the energy is returned within a certain time which depends on the amount of energy "borrowed"(E), t ~ h/E. Let's say you weigh 150 lbs = 68 kg. A rest mass of 68kg equals 6.12 x 10^18 Joules.
h = 6.62 x 10^-34 Joules-seconds
So, the maximum time you could remain in the past would be
t ~ h/(6.12 x 10^18 J)
= 1.08 x 10^-52 seconds
As stated earlier on the discussion board, the human perception of noticing ones surroundings is limited to around
80ms = 8.0 x 10^-5 seconds.
So, from this it would at first glance appear that sending something back in time would not be possible unless you were able to simultaneously send something from the past(of equal matter/energy) into the present to fill both gaps. Entropy(a measure of disorder) may be able play a role in solving this problem but I am uncertain at this time.

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<This message has been edited by pamela (edited 02 September 2000).>

If time travel is possible, then it is already happening in some time frame. If it's already happening, then we should look for evidence of it.

Pam,
I was referring to the amount of time a person from the present could remain in the past without violating conservation of matter and energy. Since, your presence in the past would increase the amount of matter/energy in the universe. As I said at first glance the Heisenberg uncertainity principle would provide away around it, but it only gives a time on the order of
10^-52 seconds to which that amount of matter/energy could remain in the past.

P.S.

1.08 x 10^-52 seconds is not 52 seconds, it is
0.000000000000000000000000000000000000000000000000000108 seconds

At any given time, there are probably enormous fluctuations between energy and matter throughout the universe. A few time travelers won't upset it.

Instead of sending something physical into the past, what about sending a coherent energy form, say a radio signal or something similar. Would that eliminate a couple more problems?

.

<This message has been edited by pamela (edited 02 September 2000).>

Protons have mass? I did'nt even know they were Catholic.

:-D heheheh.

There is no problem with conservation of matter & energy. One of the key points of Einsten's space-time continuum is that the dimension of time is equal to the space dimensions. We assign to every point of the space-time continuum four numbers, x1, x2, x3, x4 (co-ordinates), which have not the least direct physical significance, but only serve the purpose of numbering the points of the continuum in a definite but arbitrary manner.
This to say that if mass & energy are conserved in a spatial displacement then they will also be conserved in a temporal displacement. Therefore, there would be no need to simultaneously send something from the past {of equal matter & energy} into the present. There would be no gaps to fill.

In 1927 Werner Heisenberg showed from quantum mechanics that it is impossible to know simultaneously, with absolute precision, both the position and the momentum of a particle such as an electron. Heisenberg's UNCERTAINTY PRINCIPLE is a relation that states that the product of the uncertainty in position and the uncertainty in momentum of a particle can be no smaller than Planck's constant divided by 4 pi. Thus, letting the change in <x> be the uncertainty in the <x> coordinate of the particle and letting the change in <px> be the uncertainty in the momentum in the <x> direction, we have (change in x)times(change in px) is ] or equal to ( h\4pi ). There are similar relations in the y and z directions.
The uncertainty principle says that the more precisely you know the position the less well you know the momentum of the particle. In other words, if you know very well where a particle is, you cannot know where it is going! The uncertainty principle is only significant for particles of very small mass such as the electrons.
The uncertainty principle is not about energy and time it is about position and momentum.
The ideal of " borrowing energy from the vacuum " based on the uncertainty principle and Planck's constant is invalid and cannot be supported.

Quantum mechanics also says, I think, that all of that only happens if there is an 'observer' present.

Excuse me? Trying to invalidate Stephen Hawking's and other's lifetimes of work in one poorly educated statement? Not likely. Uncertainty in momentum = uncertainty in velocity = uncertainty in kinetic energy = uncertainty in energy. Good enough for ya? If you couldn't borrow energy from the vacuum, how would you explain black hole radiation? Or quantum tunneling? Or, for that matter, the very existence of the Universe? Use a better search engine man - the one you're using ain't giving ya all the facts!

They call it the uncertainty principle because nobody knows exactly what in heck Heisenburg was talking about. Quantum theory is bereft of any physical analog. Its a black box of mathmatics.

Dito.."

Quantum theory merges the physical with the non-physical, the local with the non-local, mind and matter, and all dimensions. It goes way beyond relativity and other theories that only deal with the physical universe and only address part of the question.

QM has no easy-to-comprehend physical analogue. But here's one for ya: the wave/particle duality of light. That's a physical analogue, isn't it? And as counterintuitive as they come. Can you think of a better explanation than quanta? Doubtful. Maybe you just didn't understand what Heisenberg proposed, and are trying to cover for it by pretending it's incomprehensible. Everyone accepts QM, because it works so well at describing reality.

Raz, let me guess, the uncertainty principle says "a single partical cannot move and stay still at the same time".

???

That's just common sense. Of course a particle can only have one velocity at a time. Duh!

Uncertainty means that the more precisely you know a particle's location, the less precise you can be about its velocity/momentum/KE/whatever. As well as other pairs of values that are related in the same way. That so tough to grasp?

How do you measure the velosity of something if you do not know where it is first? HUMMM?

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