Can Time Travel Truly Allow Us to Visit the Past?

[pervect]

Ok, first of all, I want to make it clear that whatever we learn in school (pre-university) is called classical physics (and electricity). For most people, it is all that they will ever need to know about physics, and even for most engineers (and I dare say most physicists), they will never have to use relativity

IMO this is becoming less and less true as technology progresses.

Precision timekeeping applications now have to routinely account for general relativistic effects, so anyone involved in that field will need some familiarity with not only special, but general, relativity. GPS systems also involve relativity (of both sorts). For physicists, anyone who works with a particle accelerator will use relativity.

 

[Gonzolo]

Haven't they also tested it with super sonic jets?

I believe so, with extremely precise atomic clocks.

And pervect's post above suggests that it might have to be accounted for in GPS systems.

 

[pervect]

Here's a URL and a quote as far as relativity and GPS goes

http://www-astronomy.mps.ohio-state.edu/~pogge/Ast162/Unit5/gps.html

Because an observer on the ground sees the satellites in motion relative to them, Special Relativity predicts that we should see their clocks ticking more slowly (see Lecture 32). A straightforward calculation using special relativity predicts that the on-board atomic clocks on the satellites should fall behind clocks on the ground by about 7 microseconds per day because of the slower ticking rate.

Further, the satellites are in high orbits, where the curvature of spacetime due to the Earth's mass is less than it is at the Earth's surface. A prediction of General Relativity is that clocks closer to a massive object will seem to tick more slowly than those located further away (see Lecture 20 on Black Holes). As such, when viewed from the ground, the clocks on the satellites would appear to tick faster than identical clocks on the ground. A calculation using general relativity predicts that the clocks in each GPS satellite should get ahead of ground-based clocks by 45 microseconds per day.

The combination of these special and general relativitic effects means that, if not accounted for, the clocks on-board each satellite would tick faster than clocks on the ground by about 38 microseconds per day (45-7=38)! This sounds small, but the high-precision required of the GPS system requires nanosecond accuracy, and there are 1000 nanoseconds in a microsecond. If these effects were not taken into account, a navigational fix based on the GPS constellation would be false after only 2 minutes, and in general errors in global positions would accumulate at a rate of about 10 kilometers each day!

 

[Gonzolo]

Indeed. A further motivation for me to dive into those tensors.

 

[omin]

Suppose you swing the masses at 1 revolution per second. Clearly, the 2nd one does a greater diameter : d2, than the 1st : d1. It therefore has a greater speed, d2/t > d1/t. This is totally classical, any engineer knows this. Same frequency of revolution, but different speed.

Application of a force doesn't mean using energy : remember W = fd. If d is 0, W is zero, and f and d must be in the same direction. Our swinging masses have d and f in perpendicular directions => no energy is used (f along string, d on circle diameter).

Application of Force means energy is expressed. Distance is a consequence of the mass's Acceleration. Acceleration of this mass is a consequence of a Force exerted upon it, which requires another mass with velocity and a collision of both masses. If Distance is zero, no Force exists which means no Energy is expressed. And, if no Energy is expressed, no Force can exist.

Force is expressed when change of velocity occurs. Although the distance between the first and second clock appears to not change because of the string, they are accelerating in relation to the human who spins them. This force is applied directly to the first clock and must be maintained to keep the clocks spinning. A constant force is exerted upon the clocks and therefore is an expression of energy.

The force is split in two. There is no "appear", the speeds are completely (classically) different as I said above.

The speed (motion) is implied to be internal in the first clock, because the force upon the first clock must supply constant supply force for the second clock.

No, they are exactly the same types of force, both centripetal and static. There is no "collective speed", see what I said above.

When I think of static force, it means the movement is not as apparent to my vision and I have to use deduction to find it, where kinetic force means I notice it visually and is axiomatic. I don't see the first clock moving as much as I see the first clock. I know the first clock isn't loosing it mass where force occurs, so it looses motion outwardly to the second clock. This motion travels to the string and then to the second clock. It is a wave of energy.

What I don't know is if the wave of energy is building up toward the outside or if it's perfectly distributed.

Only a unique angular speed. But all I have said about relativity applies to linear speed (length per second), not angular (angle per second). I'm always talking about linear speed (that is what c is.).

When a constant supply of energy is supplied to this circumstance, and we isolated all outside forces upon this system (for now), we may see this in a linear way, because all things will settle as constant. So we may apply the what you are calling linear logic to it.

No energy loss at all. No flow of energy. Only balanced forces. Let's get this classical thing right before going back to relativity.

But how is the balance of forces occurring here expressed? Perfect distribution of force across the first clock and across the second clock or is there a greater density of force, thus energy being expressed in one the clocks?

Once we get through this part, we can deal with the time travel question.

 

[Gonzolo]

...constant force is exerted upon the clocks and therefore is an expression of energy.

This not how energy is defined in standard physics. When a rock is set on the ground, gravity exerts a force on the rock, the rock exerts a force on the earth, yet no energy is converted, because W = fd = f(0) = 0. For energy to be used, the rock has to move in the direction of the force. If you open a trap door under the rock, then there is energy conversion, because d will not be zero, the rock will move along the force (it will gain kinetic energy).

Imagine a spinning dumbell in space. Where is energy used? There are millions of forces between its atoms, yet it doesn't use energy at all. I don't see what you mean by "expression of energy". Any energy that is used to keep the clock in the air is to compensate for losses due to gravity (up and down oscillations, which we should ignore) and a bit for friction. In space, no energy would be needed to keep it going.

The speed (motion) is implied to be internal in the first clock, because the force upon the first clock must supply constant supply force for the second clock.

I don't see what you mean by "internal speed".

When I think of static force, it means the movement is not as apparent to my vision and I have to use deduction to find it, where kinetic force means I notice it visually and is axiomatic. I don't see the first clock moving as much as I see the first clock. I know the first clock isn't loosing it mass where force occurs, so it looses velocity outwardly to the second clock. This velocity travels to the string and then to the second clock. It is a wave of energy. I know this much.

Static forces means the forces are in equilibrium. Whereas Dynamic forces means their is movement along forces. You might call our system kinematic I suppose (not dynamic though), but in static and kinematic cases, there is no tranfer of energy. When something is already spinning (kinematic), centripetal force balances centrifugal force, but no force is along the motion.

What I don't know is if the wave of energy is building up toward the outside or if it's perfectly distributed.

There is no build up of energy, most was given in the beginning, whatever you add is to compensate for losses due to gravity (this should be ignored). There is more towards the outside though. A simpler system (without losses) is a spinning dumbell in space. You do not have to constanly supply energy to compensate losses in this case.

(mass)----(clock 1 = pivot)----(clock 2)

When a constant supply of energy is supplied to this circumstance, and we isolated all outside forces upon this system (for now), we may see this in a linear way, because all things will settle as constant. So we may apply the what you are calling linear logic to it.

If you do wish to supply constant energy (over what is need to compensate up and down oscillations), then it will be spinning faster and faster and faster and faster and this complicates things besides the point.

 

[omin]

This not how energy is defined in standard physics. When a rock is set on the ground, gravity exerts a force on the rock, the rock exerts a force on the earth, yet no energy is converted, because W = fd = f(0) = 0.

This is a contradiction in terms. We must not confuse things. The basis of the argument without this defined will make nothing intelligeable. I can't go through everything and do a logic operation without making it too time consuming. I'm not moving on until we speak clearly on this issue.

Force implies motion. Where there is no motion there is no force. Where there is gravity, there surly is motion, even internally.

 

[Gonzolo]

No problem. You must first understand that a force, as defined in physics, (and as can be extended in all fields of life), does not necessarily imply motion, and where there is no motion, there can be forces (in equal and opposite directions, such as the net force is zero). The walls of a house exert a force on the roof all the time. Yet nothing moves.

 

[omin]

No problem. You must first understand that a force, as defined in physics, (and as can be extended in all fields of life), does not necessarily imply motion, and where there is no motion, there can be forces (in equal and opposite directions, such as the net force is zero). The walls of a house exert a force on the roof all the time. Yet nothing moves.

Force always implies motion. Otherwise, potential energy would be matter of some sort that created velocity, rather than having it internalized in some way. Energy is niether created nor destroyed.

What cannot be confused here, so we can move on, is the differentiation between the momentum concept and the energy concept. Momentum is based upon vector principles and energy is based on scalar principles. The concept of momentum seems conventionally to not represent motion that is internalized or expressed in small particle high velocity forms not seen by the human eye. Energy does account for this internalized motion or unseen particle accelerations.

Energy can be traced in all forms directly sensed or deduced because the energy concept covers all known forms when motion tranfers during interaction. Momentum may not be fully accouted for because it's limited to one form, for example the visually sensed motion form implied by it's vector limitations.

Does this help with distinguishing the contradiction of say that gravity force upon the rock, the trapdoor underneath the rock is the support force, but their the net force is zero. Force is zero if we use momentum, but not energy.

Let's stick to the concept that covers all bases.

If so, let's finish the rotational motion clock example, because I want to point out the example serves as a basis to prove time travel is not possible.

 

[Gonzolo]

"Force always implies motion."

Where did you learn that?

 

[spacetime]

beleive

You say beleive? yes I beleive. But I don't know the reason. But I have faith. And I feel physics, to some extent, progresses by having faith in certain things. It may not be able to prove them.

spacetime
http://www.geocities.com/physics_all/index.html

 

[Ba]

The normal force does not imply motion neither does the frictional forces, they are counteracting forces.

 

[omin]

"Force always implies motion."

Where did you learn that?

It's been an ongoing assumption of mine for awhile. Here is the basis of my reasoning:

Since, acceleration is based upon velocity, acceleration cannot exist without velocity. Velocity is based upon speed and direction. Velocity cannot exist without speed. Speed is based upon the displacement. Speed cannot exist without displacement. Displacement is based upon measurement and motion. Displacement cannot exist without motion.

Since, force is based upon acceleration, acceleration upon velocity, velocity upon speed, speed upon displacement, and displacement upon motion, force cannot exist without motion.

 

[Gonzolo]

I see. However, be wary of personnal theories here, the Theory Development section more appropriate for that. The rest of the site uses ands stick to standard physics.

Note that each of : acceleration, velocity, and position can be zero independantly. A force is a vector which can assume any value, independantly of what it acts upon, and it is quite stricly defined mathematically. What you are introducing is basically acceleration under a new name.

It is the net force which is F = ma. If this is zero, then a is zero, but not necessarily v and x. We may well have F = F1 + F2 + F3 +... where each of F1, F2 ... can be defined as what ma would be in the absence of the other forces.. It is quite possible that F1, F2, and F3 sum together to make 0 = ma, in which case we would a mass with a = 0. Once this result is obtained, we could care less about F1, F2, F3 ... individually, but it is them that got us to a, v and x ultimately. They are quite useful in this respect. I have yet to see how you would solve such a problem with your assumption.

The spinning clocks are still interesting, see you in the other thread.

 

[omin]

When I learned to count it began with the number one, not zero. Zero has never been taught to me as a value.

This assuption I'm introducing a new theory is smattering. That's what the physics books are implying and teaching, I've checked through the classic mechnanics of atleast four, and nothing is contradictory about what I've said about Net Force equaling zero and energy concepts.

This is the proof I have to offer: Force that equals zero only means that it is not sensed and implies momentum concepts, vs. energy which accounts for the motion that seems to disappear or cancel.

Do you have proof that proves what I am saying is incorrect in representing things accurately?

And just because a book may not explain a nuance of classic physics doesn't mean it doesn't exist like: velocity is just average velocity, which means velocity never truly occurs in perfection, but acceleration does.

 

[Ba]

What about weight and normal force, these two forces and these cancel out to 0 with respect to an outside observer. And yet people still measure weight and compare it to other people's weight. Also the normal on a horizontal surface is used for friction it's there and it's needed with the coefficiant of friction to find the frictional force. Yet all together the vertical force is zero that's not to say these two forces aren't acting on it. After all it's a totally different zero force than somebody in freefall.

 

[Gonzolo]

When I learned to count it began with the number one, not zero. Zero has never been taught to me as a value.

This assuption I'm introducing a new theory is smattering. That's what the physics books are implying and teaching, I've checked through the classic mechnanics of atleast four, and nothing is contradictory about what I've said about Net Force equaling zero and energy concepts.

This is the proof I have to offer: Force that equals zero only means that it is not sensed and implies momentum concepts, vs. energy which accounts for the motion that seems to disappear or cancel.

Do you have proof that proves what I am saying is incorrect in representing things accurately?

And just because a book may not explain a nuance of classic physics doesn't mean it doesn't exist like: velocity is just average velocity, which means velocity never truly occurs in perfection, but acceleration does.

If it suits your needs, I have no problem with that. But until I learn alternative expressions for rotary motion (which I am 100% open to), I see no reason for abandoning centripetal and centrifulgal forces. The concepts have proven themselves useful beyond Newton's wildest dreams. Another example is that we couln't find the radius of the trajectory of an electron in a B-field in a simpler way.

 

[omin]

Ba,

Istn't the vertical force implied in the coefficiant of friction?

 

[Alkatran]

Otherwise, potential energy would be matter of some sort

I found that quote funny.

Anyways, energy is NOT force.

People often get confused about this concept because of electricity. They 'use' electricty. Real energy never gets 'used'. The kinetic energy in something can move it forever!

A good example is this: if energy is exchanged or expended because of forces, what happens to a rope strung between two walls? (taught) We'll say this rope won't ever break. Since there is a force being exerted on the rope it must eventually 'run out' of energy right? Then what, it can't pull at all? You could start pulling at that rope and stretch it forever!

Also, acceleration does not imply speed, it implies CHANGE in speed. Energy does not imply force and force does not imply energy. Think of it this way: I accelerated at 5 kajillion meters per second per second for 0 seconds.

How much did my speed change? Well duh, 0. There was no time for it to happen! It's THE SAME THING for force and energy. There was no distance for the energy to change over!

Don't believe me? Look at the units. Speed is acceleration * time. Energy is force * distance. For change in speed from acceleration you need time. For change in energy from force YOU NEED DISTANCE.

 

[Ba]

Istn't the vertical force implied in the coefficiant of friction?

No the coefficient of friction is the roughness of the surface, the force of friction is the coefficient times the normal force (vertical force).

 

[Gokul43201]

Omin, you are using terms that are undefined and have no rigorous physical sense. But in any case, Ba has provided two valid cases where the resultant of several forces being zero does not mean that the forces can not be detected.

 

[omin]

I found that quote funny.

Anyways, energy is NOT force.

People often get confused about this concept because of electricity. They 'use' electricty. Real energy never gets 'used'. The kinetic energy in something can move it forever!

A good example is this: if energy is exchanged or expended because of forces, what happens to a rope strung between two walls? (taught) We'll say this rope won't ever break. Since there is a force being exerted on the rope it must eventually 'run out' of energy right? Then what, it can't pull at all? You could start pulling at that rope and stretch it forever!

Also, acceleration does not imply speed, it implies CHANGE in speed. Energy does not imply force and force does not imply energy. Think of it this way: I accelerated at 5 kajillion meters per second per second for 0 seconds.

How much did my speed change? Well duh, 0. There was no time for it to happen! It's THE SAME THING for force and energy. There was no distance for the energy to change over!

Don't believe me? Look at the units. Speed is acceleration * time. Energy is force * distance. For change in speed from acceleration you need time. For change in energy from force YOU NEED DISTANCE.

Euclid made a point about the point. Is this the one you are trying to make?