robinpike

Mike, you should keep going! Challenging an accepted conclusion will always be open to... you are wasting your time, and here's why... And for want of an example from the past... What on earth were Whitfield Diffie and Martin Hellman thinking when they they thought they could devise a secure public key encryption method? It is obvious that no such method can exist, for whatever rules can be devised to encrypt a message, the rules can simply be reversed to reveal the message.

Mike, using the diagram as reference, when the mass is at the extreme right hand oscillation position, it will be at a slightly lower point than where it is drawn - in fact it will be on the path of the dotted line. So at its extreme right hand oscillation position, the mass will be at a lower point to where it is drawn on the diagram. When the oscillation then returns the movement of the mass to the left, the starting point of the mass is now slightly lower - with respect to the static point that is indicated by the meeting point of the blue line and the green line. This lowering with respect to the static crossing point of the blue line / green line is the reason why the object will fall on each oscillation - and so the oscillating mass will fall under gravity.

If I am understanding your set up correctly, the problem is the oscillation. If the mass was not oscillating, but continuing on, then if moving at the orbital speed for its height, it would (in principle) orbit the earth - since the downward direction caused by gravity matches the fall off of the surface of the earth due to the curvature of the earth. But once you change to the oscillation set up, the small downward movement incurred due to gravity as the mass moves in one direction, on oscillating into the reverse direction, that downward movement is now 'into' the curvature of the earth - not matching it.

Hi Mike, good to see you posting again. With the two masses oscillating (at orbital speed), the problem is that this is not the same as if the two masses are in orbit around the earth !? When gravity acts on a mass in orbit, there is a vector force (gravity) towards the earth. The bit that is different for your oscillating masses to a mass in orbit, is that the oscillating masses change direction (back and forth) - and when they do, they require the base to push up. If the base did not 'push up' when the mass changes direction, then its downward direction it gains due to gravity would still be present when it reverses direction, and the mass would not be moving flat to the earth's surface, but slightly towards it. (An orbiting mass doesn't change its orbital direction - other than the action of gravity - and so it doesn't have this problem.) A simple way to see the problem, is to have the two masses connected by a rod and to spin them in a circle (at orbital speed) - rather than oscillate. The spinning mass will not levitate.

If relativistic mass showed up as an increased gravitational force, wouldn't that cause problems? With respect to our frame of reference, if there was a particle moving at almost the speed of light (the particle could be anywhere in the universe), then by the same token, that particle could consider us as moving at almost the speed of light - and our sun too. If relativistic mass increased gravitational force, then would it generate the bizarre situation where our sun is seen to have enough relativistic mass to become a black hole?

Swansont, thank you for that video, it is very easy to follow. However, there is something that I am misunderstanding about the detectors that perhaps you can clarify for me. To simplify to the basics, if an electron with known spin, for example with 'up' spin because it has just passed through a vertically aligned detector, goes through a second detector which is at some other angle to the vertical, wouldn't the direction of spin of the electron as measured by the second detector always be 'up'? I am not asking about the direction of spin of the electron after it has been through the detector, just what the result of the detector gives?

Not quite! I don't see how steepness of the road is possible without motion and change being present - that is without time? Is the following causing the discussion to be at cross purposes... Are you assuming that you are outside of the system, and your looking down on the road and noting that the road changes its steepness, is outside of the concept of motion and change of the system?

This is tricky to get across easily... Using your reply... To observe requires change, to die requires change, to breathe requires change (in that the electrons in carbon and oxygen react and change), but oxygen is not required for change, and change does not require oxygen. Swansont, I appreciate your points above. There is a difficulty in using the term 'object' if the object refers to a collection of smaller objects. Discussing the rate of time only makes sense if the discussion refers to the smallest objects - that is the fundamental particles. For example, one can observe a flower growing more slowly in winter than in summer, but because the flower is a collection of objects, that is the reason why it does not make sense to use that observation to declare that time is dependent on temperature. Maybe applying the discussion to a very simple system might help. If a system has fundamental particles that all move at the same single speed, and the space in the system does not expand nor contract, then as the particles move about that space, time would be present and that time would be the same at all points in that space and the same for all the particles. Now take the observation of what happens if all the particles were to stop moving,.. not only does change stop, but time also disappears. That is why I suggest that time requires change, and time requires motion.

The above uses an example of a road changing its steepness, and the conclusion that, that kind of change has nothing to do with time. I don't think that conclusion holds true... Surely, the existence of steepness is only possible if motion is present? And because of motion, also time? Because... walking along the road and to reach the incline requires motion. And that incline is only an incline because it changes the direction of the motion. If there were no time, then either no progress is possible along the road, or the opposite, everything happens 'in no time' - in an instant - in which case the change in direction is never detected, because it is not possible to be aware of the different directions before and after reaching the incline?

The issue is what is meant by 'light simply travels vertically upward'. What is vertical is different for different reference frames. Do you mean with respect to the reference frame of the emitting source of the light?

The particular example of radioactive decay shows the problem with any counter example. That is, how do we know that motion is not involved in the radioactive decay? To show that to be the case, it would need to be demonstrated that all motion has been removed from the nucleus. Is this what you meant? That the quarks in the proton are motionless, that the gluons in the nucleus are motionless? etc. I suspect that is not what you meant though. If the approach is that the motion of the quarks and the motion of the gluons is not involved in radioactive decay - how has that been proved? Studiot, sorry I didn't follow your example, can you explain a bit more please? My view is that without change, time does not exist. I would like see an example that counters that view.

With the ball example, the ball has a horizontal component to its movement - the same horizontal component as the moving vehicle - and so it can hit the same vertical point. It might be clearer to keep to the light example to discuss the issues you have with relativity?

What is time? One way to define time is as follows... Time is a consequence of motion - since without motion there is no concept of time.And motion is a consequence of the distance between 'stuff' changing - for without distance between stuff changing there is no concept of motion.And distance between stuff changing is a consequence of time - for without time there is no concept of distance between stuff changing. That last one is not so obvious, but think of it like this - if time were to stop, then everything would 'stand still' (like in the Superman movie). Interestingly, as Eise has mentioned, the above definitions are circular. Anyway, the above appears to be one way to define what time is, although it does seem to suggest that time and motion are more abstractions of 'stuff' and space, than being things in themselves?

ajb, thanks for putting up the detailed explanation on your blog. So theories that attempt to explain gravity through an electromagnetic theory can always be discounted - that is, unless they happen to include an explanation for the following observations (which no electromagnetic theory so far has been able to do)... Light is affected by gravity (as demonstrated by gravitational lensing), but light is not affected by electric fields - for example photon-photon interaction. Acceleration of an object due to gravity is not related to the mass-charge ratio of the object, whereas acceleration due to an electric field is related to the mass-charge ratio of the object. Neutral objects are influenced by gravity (for example the orbits of the planets), whereas neutral objects are not influenced by electric fields. However, the current absence of an electromagnetic solution to the above is not proof that one does not exist, although obviously as time goes by, it would seem to be more and more likely that such explanation is not possible.

ajb, separate to EllyDlights thoughts, I would be interested to know, did you have a particular example in mind with your above comment?

I don't think that is a must - rather a possible answer is that the electron passes through both slits...

Tar, a single slit still produces a diffraction pattern http://www.math.ubc.ca/~cass/courses/m309-03a/m309-projects/krzak/ This is also true of a pin hole, so as the beam of photons pass through each pin hole, rather than filter only those photons heading for a spot on a screen, the pin holes will cause the beam of photons to spread out. And this problem would also be present if trying to direct a beam of photons to only one slit of two slits.

Thank you Janus for the help on the space-time diagram (and the others on this topic), it will take me a little while to digest the information as there is quite a lot to take in. As regards the meaning of 'actual' and 'perceived', if two view points are contradictory, then at least one of those view points must be perceived and not actual. For example if twin A sees twin B's clock run slower, and twin B sees twin A's clock run slower, then at least one of their view points must be perceived and not real. This deduction is of the form: If A > B and B > A, then one of those statements must be false. The result of line of sight and perspective is a simple example of the above. Twin A and twin B stand next to each other and note that they are of the same height. Twin A walks away from twin B and after a while, turns around and sees that he can obscure his view of twin B by holding up his thumb in front of his line of sight - with a perceived sense that his twin is now smaller than he is. Twin A can also do the same to his view of twin B - with a perceived sense that his twin is now smaller than he is. Both of these situations cannot be true, at least one must be false. In this example, both are false as the twins are still the same height as each other, the perceived effect is down to perspective. In relativity and the twin paradox, after the twin B's journey, his clock has less time on it, so we know something happened to his time - an actual change has occurred. The reason why I want understand the space-time diagram, is because the loss in time of the travelling twin's clock cannot be due to a slowing down of time of his clock - that must be only a perceived effect. The reason being that if the travelling twin's clock were slowed down, i.e. a slow down in his rate of time, relativity has no means of returning that rate of time back to 'normal'. I.e. when he returns back to earth and their two clocks are seen to be running at the same rate, but the travelling twin's clock has a lesser time on it. There is no difference between acceleration and de-acceleration in relativity. If acceleration were to slow down a clock for real, then de-acceleration would also slow down the clock for real (according to relativity). My understanding of this is that 'the rate of time' never changes for the travelling twin. But he did lose time on his clock. This is why I want to understand the space-time diagram, as when in the past I have discussed the above point on acceleration / de-acceleration, it was mentioned that the space-time diagram explains how the travelling twin lost time on his clock. And this is what I want to understand.

When the phrases time dilation and length contraction are used, what do these really mean? For example, say in the travelling twin paradox, there is a perceived time dilation that both twins observe happening to the other, as the travelling twin sets off (and a perceived time contraction as the twin returns). I understand these meanings - perceived because it is a consequence of the twins moving away from each other, each twin observing the same perceived time dilation as the other. But I have also seen time dilation being used as an actual time dilation - i.e. in the sense of 'rate of time' slowing down - and that I do not understand? If the travelling twin really experienced a slow down in his rate of time, then by what action does his 'rate of time' return back to 'normal'? The explanation that I have been given on this, is that the rate of time (not perceived) never changes for the travelling twin, but rather the distance of the travelling twin's space-time line is shorter than the stay at home twin's space-time line. So the travelling twin's rate of time does not change, but because his space-time line is shorter, his clock has gone through fewer 'ticks'. This look a bit odd on a space-time diagram, as the travelling twin's space-time line looks longer on the diagram. I do not understand space-time diagrams to know if that explanation is valid or not. Could someone help and explain what a space-time diagram really represents and how this all works. The same argument applies to length contraction - if actual length contraction really occurred, then by what action could the 'contracted length' return to 'normal'?

Thanks, so if I am understanding this correctly, multiple electrons undergoing the same acceleration (under exactly the same conditions) emit equivalent photons and the same number of those photons? And the rate of production of the photons and their wavelengths is related to how quickly the change in the magnetic and electric fields occurs due to the accelerating electron. So it is not the electron 'that remembers' from moment to moment what acceleration it has undergone - it is the increase in the magnetic and electric fields that contains the 'preparation of the creation of the photon' from moment to moment? If that is a valid way of looking at this, it resolves my query - thanks.

No that was not the intention. If I am understanding this correctly, when a free electron is accelerated, it will emit radiation. The query is around at what point does the electron emit the radiation? Does it emit a 'sizeable' photon after a certain period of time under acceleration? Or does it emit a 'continuous stream' of very weak photons of the smallest energy? If the observation is the former, then there is the question as to how the electron is 'remembering' the amount of acceleration it has recently received, in order to emit the photon equivalent to that 'cumulative acceleration'? I know that in the atom, the radiation is emitted as a single photon, corresponding to the difference in the start and next orbital the electron moves to. But here the query is around the acceleration of a free electron, another example being that of an electron spiralling in a magnetic field.

And from the electron's point of view, I'm taking that the following is correct? The electron is motionless when a nucleus goes whizzing by, causing the electron to move. The closer the nucleus passes the electron, the greater the acceleration on the electron - and it is this 'greater acceleration' that equates to, in the reference frame of the nucleus, the statement: the distribution depends on the 'angle between the motion of the electron' and the acceleration? So exactly how does that work? For example, the electron accelerates in a gravitational field, heading towards the centre of mass of the object. At what point, or points, does the electron emit radiation? Looking at it from tiny increments, at each moment, the electron can be considered to be at rest when it receives a tiny acceleration from the gravitational field. The next moment can then be considered, the electron again can be considered to be at rest when it receives another tiny acceleration from the gravitational field. And so on. So on that basis, which tiny acceleration triggers the emission of radiation? In fact, I realise the same question can be asked for the example of the electron passing the nucleus. Looking at the electron from moment to moment, at what point does the electron emit the radiation?

Studiot, yes, that is how I understand the scenario. The two observers see different distances and different times (and the frequency of the light is different) from their position in space and the source of the flash of light. I was just wondering if it is valid to consider what the light 'sees' - i.e. in the 'distance' and 'time' from its source to when it meets / passes an observer in space? I suspect we are unable to answer, and so suspicious that we are misunderstanding something about space, time and light. Anyway I am interested in people's thoughts on answering such a question.

Studiot, thanks for the maths (and no worry about the typo's). So for my simple scenario, we can use the maths for the 'moving' observer, and we can use the maths for the 'standing still' observer, but am I right in thinking that the maths cannot be used for the flash of light (or at least if used it it is meaningless)? If that is the case, what is the maths that can be used for the flash of light?

Hi Christopher - I am sympathetic to your questions. The two lightning strike thought experiment appears to be able to be reduced down to understanding this simple scenario... A 'moving' observer, say going to the right, passes a 'standing still' observer and at the point of passing, a flash of light is created ahead of them from the right that moves towards them both. Obviously, the 'moving' observer is going to see the flash of light first. However, with the light approaching each observer at the same closing 'speed of light', and each observer at that point being the same distance from the light, how is this possible? The explanation would seem to require a mention of how length as well as time is perceived? However, the videos that have been included in these posts on the two lightning flash thought experiment do not seem to require length contraction in their explanation. So perhaps it would help if someone, for the above simply stated scenario (rather than the two lightning flash thought experiment), could describe what the complete explanation is, one from the 'moving' observer's point of view, and one from the 'standing still' observer's point of view. I would like to understand those explanations first and then I may have some more questions. Thanks.