The Naked Scientists Forum

another_someone

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« Reply #25 on: 10/07/2006 02:07:46 »
quote:
Originally posted by thebrain13
Come on, you gonna let me get away with that?

OK, this one slipped off my radar, but you're right, I'm not gonna let you get away with that

quote:
Originally posted by thebrain13
okay i've been away for a little while, where to start. first off, your initial rebutal says, acceleration is not relative, or you can tell that you are accelerating. This is simply not the case, you can only tell you are accelerating relative to another object. For example, if you are driving a car and you hit the gas, you consequently feel a push from the seat, this is not because YOU are accelerating but the car is, and is pushing you forward. So lets say you painted the windows black and you hit the gas again, this time some force from within your body is pushing you forward, so you and the car are accelerating equally. In this case, you dont feel any push, so how do you SENSE you are accelerating?

The problem here is that there is no such thing as a force from within your body, the force must always be from without.  Nothing, absolutely nothing, will accelerate unless it is subject to some external force (this was made clear in Newton's first law of motion, and remains true even in a relativistic world; Newtons second law of motion has had to be modified by relativity)..

quote:

Secondly, lets not deflect attention to acceleration because although einstein does say, only inertial frames of reference are equal, einsteins' time dilation equation is not based on acceleration, it is based on relative velocities. And this phenomena does not soley exist in the moments an object is non inertial.

Yes, the equations pertaining to special relativity only relate to relative velocity, but Einstein makes it clear that the equations are not valid for accelerating bodies, and so the fact that the equations do not address the issue of acceleration is not relevant.

If special relativity was pertinent to accelerating bodies, then Einstein would never had gone to the trouble of developing general relativity.  It is general relativity that pertains to accelerating bodies, but since the maths surrounding general relativity are considerably more complex than those pertaining to special relativity, I have never really got to grips with the mathematics of it.

In a sense, the difference between two bodies at constant velocity, and a body at accelerating velocity, is that: two bodies at constant velocities can only relate their velocities to each other; whereas a body that is accelerating can compare its present velocity to the velocity it had at an earlier time – so yes, it is relative, but relative to itself.

quote:

It seems like I still see the same mistakes I was talking about in my last post, with your rebuttal of my statement, why doesn't stella view a redshift. you say it is a question of how long terrance will be redshifted. So my fourth bold statement is,
WHY WOULDNT STELLA VIEW TERRANCE REDSHIFTED AS LONG?

You also state that it is not a question of wether terrance will view stella to turn around but when.
So my fifth bold statement is
WHY WOULDNT STELLA VIEW TERRANCE TURNING AROUND AT THE SAME TIME?
To get to the heart of my argument, how can you distinguish between two objects using relative motion, when both motions have to be exactly equal at all times?

The reason why they do not see things happening at the same time is because relativity causes a distortion of time.  It is even possible, in a relativistic world, to two observers to see the same thing happen, and yet one will swear that event A took place before event B, while the other will swear that even B took place before event A.

quote:

you also say I am paying to much attention to the visual, I dont think so, all experiments are observed not sensed. Although im not sure where you were going with that.

Are you telling me that a blind man cannot carry out experiments?

It is true that we are most used to carrying out experiments with visual instrumentation, because our visual senses tend to be the most precise; but we do actually have accelerometers that will measure acceleration, and provide a visual readout of how much a body is accelerating.  I was merely using the example of our own internal inertial sense as a way that you might have personal experience of the force associated with acceleration, but we also have electronic devices that can provide the same information in visual form.

quote:

Also, I just glanced over your second post, you say,I don't know the exact ways it resolves itself, but what one can say is that pilots a and b do not, and cannot, exist in isolation, but exist within the context of the wider universe, which does influence the space within it, and so these pilots, in their space ships must have a motion relative to the motion of the total universe.

This is a blatant example of absolute motion. Given newtons third law, every action has an equal an opposite reaction, the overall motion of the universe has to remain constant, or absolute, you might say. so anything relative to the universe as a whole is as absolute a velocity as they come. Secondly, this is clearly not what einstein was saying, he says any non inertial frame of reference is equally valid, not just the frame of reference which is, the entire universe.

There is nothing that I have said that violates Newtons third law.

As you say, in order for Stella to be able to accelerate, there must be a force acting upon her, and that force must create a reaction force on something else, thus the inertia of the universe is conserved.  This is the difference between Stella and Terrance, since Terrance is not accelerating, there is no force acting upon him, so there is no reaction force that must act upon something else.  But all of this pertains to acceleration, not to velocity.

George
« Last Edit: 10/07/2006 02:08:30 by another_someone »

thebrain13

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« Reply #26 on: 10/07/2006 17:22:10 »
When I said, come on you gonna let me get away with that, I actually meant to post that on my other post, what is distance, since nobody was responding to it. Anyways it seems that since I implied that I obviously errored some place, it ignited a fire of posts, but I really didn't think I said anything false.

Okay so, when I said if a force was acting on your body and the car unifomly, I wasnt implying that I knew of machines that did so, Einstein didnt have to know how to make floating elevators in outer space and build trains that can approach the speed of light. And I didnt think that baseball players would be able to hit baseballs 99.999999999 percent the speed of light, I was assuming if you could.

If you need more examples, why dont you ask a goldfish? whose body is exactly the same density as water(in real life its just similar, were assuming here people) fill his fishbowl completely with water, so no air remains, and seal the top. Make sure you paint the bowl black so he can not see outside. Now accelerate the bowl all you want, in a perfectly controlled experiment he has no way of knowing how much he accelerated.

If any object is accelerating uniformly with its surroundings, no experiment can be done to determine acceleration. Unless you fellas can think of one?

To solvay  your link, is probably the most confusing one i've ever read, that didn't make sense at all. He says, both trains are accelerated equally on parallel tracks from earth to alpha cenauri. Then he jumps right into saying that they both wont make it to earth at the same time. Why the hell not? Why he makes that jump, who knows. I'd be surprised if anybody understood that.

Both solvay and anothersomeones arguments, imply absolute motion to explain this paradox. And Einstein made it clear, there is no such thing. Solvay, your implying that merely by being accelerated that makes you the prefered reference frame, and by being this prefered reference frame, changes the outcome of a given experiment. That is contrary to what Einstein was saying and that is absolute motion. And anothersomeone, even being relative to where you were is an absolute quality. I also never said you were violating newton (newton believed in absolute motion) when I brought his third law up, I was just using it to show you that the universe(as a whole) never accelerates or decelerates, in any direction. Setting motion relative to an anchored object like, the entire universe, is also implying absolute motion. Einsteins relative motion means relative to one other, only one specific object. Setting yourself relative to many objects, screws everything up.

You guys need to break yourselves of always thinking of everything in absolute terms, or you will never understand special relativity. Special relativity works with every object, relative to every other object. If you need to bring in more than one reference frame to explain this phenomema, then you are contradicting Einstein.

another_someone

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« Reply #27 on: 11/07/2006 01:55:07 »
quote:
Originally posted by thebrain13
Okay so, when I said if a force was acting on your body and the car unifomly, I wasnt implying that I knew of machines that did so, Einstein didnt have to know how to make floating elevators in outer space and build trains that can approach the speed of light. And I didnt think that baseball players would be able to hit baseballs 99.999999999 percent the speed of light, I was assuming if you could.

If you need more examples, why dont you ask a goldfish? whose body is exactly the same density as water(in real life its just similar, were assuming here people) fill his fishbowl completely with water, so no air remains, and seal the top. Make sure you paint the bowl black so he can not see outside. Now accelerate the bowl all you want, in a perfectly controlled experiment he has no way of knowing how much he accelerated.

But you are missing the point, the very point that you yourself raised, Newtons first law of motion, that each and every force has an equal an opposite force  applied to something else (i.e. that a force does not act upon an isolated object, but that a force operated between two separate objects).  This is what is different between a constant velocity, that does not require any force acting upon it (in fact, it must not have a force acting upon it – Newton's first of motion), and an accelerating body that must have a force applied in order to make it accelerate (Newton's first and second laws of motion).

quote:

If any object is accelerating uniformly with its surroundings, no experiment can be done to determine acceleration. Unless you fellas can think of one?

This is not true.  Even if you have a solid lump of iron, and that lump of iron is being uniformly  accelerated by a magnetic field, you can still attach an accelerometer to the lump of iron in order to measure its acceleration.

Even if you had not yet invented accelerometers, you could determine that the lump of iron is being pulled by the magnet by looking at the reaction in the magnet itself (Newton's third law, that every force must have an equal and opposite, and the force applied to the lump of iron will have an equal and opposite force measurably applied to the magnet itself.

quote:

You guys need to break yourselves of always thinking of everything in absolute terms, or you will never understand special relativity. Special relativity works with every object, relative to every other object. If you need to bring in more than one reference frame to explain this phenomema, then you are contradicting Einstein.

This is where we started out, and what you say is categorically wrong, all that special relativity pertains to is inertial systems.

http://en.wikipedia.org/wiki/Special_relativity
quote:

The theory was called "special" because it applies the principle of relativity only to inertial frames.

http://en.wikipedia.org/wiki/Inertial_frames#Equivalence_of_inertial_reference_frames
quote:

A fundamental principle of all physics is the equivalence of inertial reference frames. In practical terms, this equivalence means that scientists living inside an enclosed box moving uniformly cannot detect their motion by any experiment done exclusively inside the box.
By contrast, bodies are subject to so-called fictitious forces in non-inertial reference frames; that is, forces that result from the acceleration of the reference frame itself and not from any physical force acting on the body. Examples of fictitious forces are the centrifugal force and the Coriolis force in rotating reference frames. Therefore, scientists living inside a box that is being rotated or otherwise accelerated can measure their acceleration by observing the fictitious forces on bodies inside the box.

George

another_someone

• Guest
« Reply #28 on: 11/07/2006 02:24:36 »
quote:
Originally posted by thebrain13
You also state that it is not a question of wether terrance will view stella to turn around but when.
So my fifth bold statement is
WHY WOULDNT STELLA VIEW TERRANCE TURNING AROUND AT THE SAME TIME?

http://en.wikipedia.org/wiki/Relativity_of_simultaneity
quote:

Relativity of simultaneity means that events that are considered to be simultaneous in one reference frame are not simultaneous in another reference frame moving with respect to the first. For example imagine there were volcanoes located on Mars and Venus. We on earth may see these two volcanoes on the different planets erupt and conclude (after appropriate corrections for light travel) that the eruptions were simultaneous; we could calculate the Greenwich Mean Time at which the eruptions occurred. The inhabitants of a distant galaxy, travelling away from ours at a great speed, may one day observe these same eruptions and find that they were not simultaneous, that one occurred before the other. The concept of “simultaneous” or “simultaneity” is not an absolute, but a relative property – it depends on one’s frame of reference.
In Einstein’s Special Theory of Relativity, relative simultaneity seems to be inextricably linked with the (logically) separate phenomenon of time dilation, which concerns the different rates at which time passes (or identical clocks tick) in two different reference frames. However these two different things are not necessarily linked. For example, Einstein’s (1960) demonstration of relativity of simultaneity (lightning strikes both ends of a moving train, seen as simultaneous on the embankment but not on the train) makes no reference to clocks or the rates at which they are running. No conclusions need be drawn about the rate of moving clocks from this example alone.

George

thebrain13

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« Reply #29 on: 11/07/2006 19:17:44 »
how do you put links in posts?

another_someone

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« Reply #30 on: 11/07/2006 19:24:04 »
quote:
Originally posted by thebrain13
how do you put links in posts?

I suggest you read through: http://www.thenakedscientists.com/forum/faq.asp

George

thebrain13

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« Reply #31 on: 11/07/2006 20:17:56 »
Um actually, I dont really feel like learning links right now, anyways I just did a little research on the "relativity of simultaneity" Google that in parenthesis and click on the first link. I think this is really the misundetstood part of relativity, this is what really makes everything work, but hardly anybody ever references. Including almost all explanations of relativity I've seen, who WRONGLY, explain something without referencing it, or at least use it to explain things like relative velocity.

thebrain13

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• Posts: 442
« Reply #32 on: 11/07/2006 20:25:50 »
And to anothersomeone, your accelerometer would not work if it was accelerating uniformly with whatever it was measuring. Im not talking about accelerating it by pushing a side of the accelerometer. The meter has to be uniformly accelerating with its surroundings. Would your meter work free falling in a gravitational field? Key word, free falling. Also there is a big difference between using internal systems and using absolute motion.
« Last Edit: 26/07/2006 02:19:53 by thebrain13 »

another_someone

• Guest
« Reply #33 on: 11/07/2006 21:10:12 »
quote:
Originally posted by thebrain13
Um actually, I dont really feel like learning links right now

quote:
Originally posted by thebrain13
And to anothersomeone, your accelerometer would not work if it was accelerating uniformly with whatever it was measuring. Im not talking about accelerating it by pushing a side of the accelerometer. The meter has to be uniformly acclerating with its surroundings. Would your meter work free falling in a gravitational field? Key word, free falling. Also there is a big difference between using internal systems and using absolute motion.

Gravity is a whole different issue, which is where general relativity comes in.

What general relativity says is that if you are free-falling in a gravitational field, you are simply following the natural curve of space (in other words, it is the person who appears to be stationary who is actually accelerating in space, and the person who is free-falling is actually not accelerating at all – this is exactly what an accelerometer would tell you).

http://en.wikipedia.org/wiki/General_relativity
quote:

gravitation is not due to a force but rather is a manifestation of curved space and time, this curvature being produced by the mass-energy and momentum content of the spacetime

One of the defining features of general relativity is the idea that gravitational 'force' is replaced by geometry. In general relativity, phenomena that in classical mechanics are ascribed to the action of the force of gravity (such as free-fall, orbital motion, and spacecraft trajectories) are taken in general relativity to represent inertial motion in a curved spacetime. So what people standing on the surface of the Earth perceive as the 'force of gravity' is a result of their undergoing a continuous physical acceleration caused by the mechanical resistance of the surface on which they are standing.

George

thebrain13

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« Reply #34 on: 11/07/2006 22:17:52 »
I knew I would get that response if I brought up gravity. That free falling accelerometers don't work because gravity doesn't "really" accelerate things. Regardless of that, if you accelerate an accelerometer, uniformly with its surroundings it still gets no reading. Even if you don't use gravity.

another_someone

• Guest
« Reply #35 on: 26/07/2006 02:27:55 »
quote:
Originally posted by thebrain13
I knew I would get that response if I brought up gravity. That free falling accelerometers don't work because gravity doesn't "really" accelerate things. Regardless of that, if you accelerate an accelerometer, uniformly with its surroundings it still gets no reading. Even if you don't use gravity.

So what force (or pseudo force) would you use that would equally accelerate all parts of the accelerometer.

Any force that would behave in this way would be so much like gravity as to be indistinguishable from gravity, and so why would you not call it gravity.

Every other force you care to name behaves differently upon different types of matter, and so you could always construct an accelerometer using whatever type of matter was not affected by this force.

George

thebrain13

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« Reply #36 on: 26/07/2006 04:07:05 »
Einsteins equivalence principle explains that all uniform acceleration acts exactly the same as gravity, so of course my example would act like gravity, thats inevitable. And since you cant distinguish between the use of gravity and whatever force(s) I use, granted they are under uniform acceleration like I explained in my experiment, the use of gravity wont affect the experiment.

In otherwords einstein is saying your accelerometer wont read anything, regardless of if it is in freefall or under uniform acceleration.

another_someone

• Guest
« Reply #37 on: 26/07/2006 17:05:00 »
But you have said that your hypothetical force is like gravity, but it is not gravity – do you have the least evidence that such a force actually exists.  If such a force does not exist, then your scenario does not exist.

The only force that operates at large distance other than gravity is the electromagnetic force, but the electromagnetic force can easily be distinguished from gravity.  Are you saying that you have discovered another long range universal force?

George

thebrain13

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« Reply #38 on: 26/07/2006 19:39:30 »
you can use multiple forces, in whatever magnitudes. Your argument is that it is impossible to accelerate an object uniformly without using gravity, that is not the case.

ukmicky

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« Reply #39 on: 26/07/2006 22:30:20 »
quote:
Originally posted by thebrain13

you can use multiple forces, in whatever magnitudes. Your argument is that it is impossible to accelerate an object uniformly without using gravity, that is not the case.

What other forces  can act on and  accelerate  every single atom in a body equally or how would you use multiple forces to act on every atom equally

Michael
« Last Edit: 27/07/2006 00:41:39 by ukmicky »

thebrain13

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« Reply #40 on: 27/07/2006 01:04:31 »
yes, use multiple forces to accelerate the atoms equally.

another_someone

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« Reply #41 on: 27/07/2006 01:23:44 »
quote:
Originally posted by thebrain13

yes, use multiple forces to accelerate the atoms equally.

But you have still evaded answering the question – what is the force, or what are the multiple forces, you would use.  To say there are more than one of them does not tell us what they are.

George

thebrain13

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« Reply #42 on: 27/07/2006 01:28:18 »
electric charge

another_someone

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« Reply #43 on: 27/07/2006 01:57:38 »
But electric charge has no effect upon electrically neutral entities.

Electric charge has no effect upon a neutron at all.  Electric charge has an opposite effect upon the electrons and the protons within an atom, and so the overall effect upon an electrically neutral atom will be nothing at all.  Furthermore, electric charge, although it can have a polarising effect upon photons, it will not cause and attractive or repulsive force upon a photon, since a photon is also electrically neutral (and the red shift in a laser or radar beam could be used to construct an accelerometer).

George

thebrain13

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« Reply #44 on: 27/07/2006 02:50:13 »
Then use Electric charge, and Nuclear strong force. Cant you just drop this argument? The only way you can win is if you prove that accelerating an object uniformly is impossible. Which makes einsteins equivalence principle meaningless. Im implying if you did, what would happen, I dont need to make the experiment.

another_someone

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« Reply #45 on: 27/07/2006 03:42:35 »
quote:
Originally posted by thebrain13
Then use Electric charge, and Nuclear strong force. Cant you just drop this argument? The only way you can win is if you prove that accelerating an object uniformly is impossible. Which makes einsteins equivalence principle meaningless. Im implying if you did, what would happen, I dont need to make the experiment.

Photons, neutrinos, and much else are effected by neither electric charge nor the strong nuclear force.

Protons are neutrons are effected by the strong nuclear force, but the range of the strong nuclear force is so short that it cannot be felt outside the nucleus of the nucleus of the atom, so there is no way of using it to effect a group of atoms.

Einstein only postulated two equivalences – that if inertial reference frames, which is not the case we are discussing; and that between uniform acceleration (caused by the curvature of space) and gravity.  He made no suggestion that anything but a curvature of space itself could cause the kind of equivalence that you suggest.

George

thebrain13

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« Reply #46 on: 27/07/2006 03:53:01 »
yes he did. Why do you think he called it the equivalence principle?

Because gravity is equivalent to uniform acceleration.

What Einstein never says, is only gravity can create uniform acceleration. Unless you can find where he says that, in which case, I stand corrected.

heikki

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« Reply #47 on: 27/07/2006 11:20:06 »
quote:
Originally posted by thebrain13

lets say there are two spaceships containing one pilot each, they are identical twins of course. We'll call them pilot a and pilot b. pilot b fires his engines and travels at 99 percent the speed of light away from pilot a for one year. Then turns around and comes back. Einstain says that from pilot a's perspective pilot b would have aged less than him. However Since velocity is relative to each observer, pilot b sees pilot a speeding away from him and then returning. So pilot b should see a younger pilot a. So my question is when the two meet each other after the trip which one is younger?

Hi, Thebrain13.

I both pilot travells 1 earthyear then they both are same age. If hundred year then they are 100year. Still same age.

If travelling speed is different a and b, x m/s, still s is actual same both. Only m is different and changed.

Can use timeunit, earth s or "constant" s, still 1s is 1s. What else it can be? 1s cannot be 1/2s or 2s.

Therefore my answer to your question is that both space-traveller going do aged at same time. Of cource and because our body is like other mammals fir to earth nature through many and many generation it control that ageing-process and different speed on space can happend some genetical-cell basic changes and then other traveller can be little seems yonger, but still, earth-year-age is same.

tarbag

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« Reply #48 on: 27/07/2006 22:49:11 »
quote:
. Einstain says that from pilot a's perspective pilot b would have aged less than him.

According to the experiment of Michelson Morely we deduce that the theory of special relativity  is valid for the light signals or the  electromagnetic waves.Why thus apply it for material bodies. It is not  a confusion here.
Well cordially

another_someone

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« Reply #49 on: 26/07/2006 17:05:00 »
But you have said that your hypothetical force is like gravity, but it is not gravity – do you have the least evidence that such a force actually exists.  If such a force does not exist, then your scenario does not exist.

The only force that operates at large distance other than gravity is the electromagnetic force, but the electromagnetic force can easily be distinguished from gravity.  Are you saying that you have discovered another long range universal force?

George