MigL

No it doesn't ! Everything 'sees' its own local landscape ( remember the finite c). If your 'landscape' includes a black hole for example, you will 'see' it recede into the distant past, as, from your frame, time has stopped at the event horizon.

I'm not going to present any arguments relating to definitions, dictionaries, or bachelors ( ? ). I am gonna throw this out there again, though, Eise, as I don't think you gave it enough attention previously... In post #181 you say "change is more fundamental, as a reference, than time, because we can observe change, but we cannot see time, except through changes" which is absurd, because without the passing of time NOTHING CHANGES ! So you cannot observe any changes without passing of time. Ever ! On the other hand, you can make the argument that time can pass without any change occurring ( numerous members have presented examples which won't be repeated ). So which is the more fundamental ? Or do you wanna argue the definition of fundamental ( kidding ) ?

I, on the other hand, would say that a single you extends into the past from the day you were born, through the 'present', and into the future to the day you die. Of course your body and bones and dust will extend even further, but they'll cease moving in the spatial dimensions, such that their space-time graph will be a vertical line. It will still be a single you but at differing time ( and sometimes space, as that is optional ) co-ordinates. It is not you that is moving in the time dimension, nor is time moving, rather what we consider our local 'present' or 'now' that is continuously translating along the time dimension. The 'present' or 'now', is of course different for everything because of a finite c. Note also that the 'present' or 'now' will proceed at differing rates depending on the space-time curvature of the local frame. It is analogous to being in a train ( since you like that analogy ) and looking out the window. The window is what we can interact with as it represents the local 'present' or 'now', and the changing view out of the window is the time 'landscape'. The landscape or time is immobile; it is the window or 'present' that is moving from the past to the future landscape. The local 'present', in effect, carries us through the time dimension, and it only moves in one direction ( except possibly at really small scales, but that's an argument we'll have another day ). I hope that's a little clearer than mud.

In Switzerland, IIRC, every male of legal age is required by law to keep a rifle in their home and to serve 2 weeks per year, as they are all members of the armed forces. These aren't necessarily handguns of course, but... They don't shoot each other or the police !

Say you have a pool table with balls in various locations on it. You have all pertinent information about the system, and you set one of the balls in motion. It is fairly simple to create a computer program that calculates all future interactions of the balls, and can predict their future positions and momentums. This is completely deterministic. Now consider an infinitely large and fast computer which could be fed all information about every particle in you body and surrounding environment. Using laws of physics, it would also be able to predict all future positions, momentums charges, etc, of all those particles in your body. Including the particles that make up your mind and thinking processes. It would be able to predict all your decisions. If an external 'observer' can predict your decisions, they are pre-determined by definition, and you don't have free will. This is if the system was deterministic. You and I have had this discussion before Eise, and I'm afraid I still haven't changed my mind. Quantum mechanics, or more specifically the HUP, makes it impossible to know the initial state of all particles comprising a system ( like your mind ), so it is impossible to predict or pre-determine a decision. If it cannot be predicted, then there is no constraint on your will. In effect, the Heisenberg Uncertainty Principle is the source of our unpredictable free will.

Nonetheless he does make some valid points, as does the opposition. A very interesting discussion so far, it has certainly made me think. And civil too, a refreshing change.

Michel123456, why would a co-ordinate change ? And why would it take time to change assuming it could ? A co-ordinate is a FIXED reference point on a 4D grid. Events, or things, can occupy different co-ordinates as they move or age. Using (x,y,z,t), it takes I unit of time for an event's present to go from (0,0,0,0) to (0,0,0,1). Note that it has not moved. The alternate motion from (0,0,0,0) to (1,0,0,0), is NOT ALLOWED as it implies instantaneous motion and disregards c. so your question is meaningless. You will never be able to see events in your own past. That is not what a light cone represents. You cannot separate fast enough from an event so as to outrace the light coming from that event ( on sub-cosmological scales anyway ).

If time were a train, we would call it a train. There is no duplication of you in old co-ordinates, nor is there vacating of old co-ordinates when time progresses. You were, are, and will be, at every co-ordinate you remember, are, or will be in the future ( disregarding QM effects ). Why can you not grasp that time does not behave like position ( or atrain for that matter ). That is what the best theory we have, that describes the properties of time, tells us. Until something better than GR comes along, this is what we have. Suck it up.

I count three different topics being discussed here, including Woodsong's mixed-up ideas about black holes. Its getting rather confusing. Maybe time to start splitting-off topics ?

So you lied when you agreed to all those points earlier ( 3 posts ago )? Or are you indecisive and change your mind a lot?

True. But Fermat's principle is a subset of the principle of least action.

Fermat's principle of least time is a generalization ( or is it the other way around ? ) of de Mauripitus' principle of least action, as it applies to massless particles ( such as light ) only.

Because it still isn't and will never be an absolute frame. Same as there's no universal 'now'. Why not just say 'I know I'm wrong" as you have, and add 'I will try to learn from books and other's knowledge', instead of incessantly bringing up unrelated stuff like death by cosmic rays ( ?) and being so verbose.

Since we define a 'straight' line with light, it must obviously travel that line. More exactly, light follows the curvature ( if any ) of space-time. You would only be able to see a 'straighter' line if you were 'outside' space-time. i.e. That's as straight as your gonna get. Edit: Oops. Thought I was on 1st page, but actually 3 pages in. Old subject/OP.

This is just what was needed. Another thread on the existence/meaning/cause of time. Edit: My apologies to the OP. This one came first.

This discussion between you, Eise, and swansont, has been extremely interesting, if a little philosophical recently. You insist time is an abstraction of change, and cannot be independently defined. In effect, there is no time without change. Yet how can you define change without using the concept of time ? You cannot have change without the passage of time. By your standards, change is also an abstraction as it doesn't exist without time. So what are you saying, time is an abstraction of another abstraction ?

I thought I had been pretty clear in my explanation, but I guess I and others are just banging our heads against the wall. As the balloon rises it does gain GRAVITATIONAL potential. That potential makes it want to fall. That is what gravity does. The buoyant force also has an associated potential, which makes the balloon want to rise. Since the balloon IS rising, the buoyant force is overcoming the gravitational force, and the net negative potential is decreasing. Note that positive and negative here, are just arbitrarily assigned to up and down directions In other words, the balloon is gaining kinetic energy upon release, so its net potential is decreasing. End of story. I don't care who you ask. If you'd rather go discuss this with your Professor friend, be my guest.

YES !

The closest we can come to an absolute frame is the CMB. We can easure our velocity with respect to the observable universe by the amount of blue shift in the direction we are heading and the red shift in the opposing side ( the direction and speed we come from ). The CMB is isotropic to 1 part in 10000, so the blue and red shift are readily evident. This is still not an absolute frame as there is no such thing !

Michel123456's problem seems to be that he is considering concentric spheres, and that in each further additional sphere,things are moving farther apart. He cannot reconcile expansion with past time/distance. He is inside an expanding observable universe, but expects to be able to look far enough away to be able to see the original compactified,post big bang universe. As if he were outside it !!! Miche123456, consider looking outwards radially along one direction, analyse the observational evidence, and then draw your conclusions. Remember,you are INSIDE the expanding universe.

Owww... Not so loud !

And that's why nobody considers psychiatry, forensic or otherwise, a science, Willie71.

Oh this is getting ridiculous. We know the mass of the balloon and can determine the mass of Helium filling it. Considering only the vertical axis, when the only force acting on this mass is gravity, we know that potential is exchanged for kinetic , i.e.motion downward. This is what happens on the airless moon, for example, and can be easily calculated. If there is more than one force acting on it, but of a negative nature such as bouyancy due to the atmosphere,the potential may be combined,but it is still exchanged for kinetic motion as long as the balloon is not constrained. If the motion of the balloon is now vertically upward, then we know that the negative bouyant force has a greater magnitude than the gravitational force such that the net force is negative and upwards. One easy way to check this is to use the same amount of Helium,but filled into a heavier, metal balloon,such that the force of gravity acting on the greater mass. is able to overcome the bouyant force , which hasn't changed. Incidentally this is the first time I've seen one side of an argument state... 'I disagree with you, and when you come around to my point of view, and can explain it to me, then I'll give my argument' I hope I don't see it again.

Your assertions may not be required or provable with current accepted theory, yet you may get the last laugh. LQG certainly considers space at the Planck level 'granular', or a 'fabric' of interlocking loops. And the reference to Witten and string theory/non-commutative geometry in your Wiki link suggests string/M theory may have a degree of quantization also. I look foreward to the day when I offer you my apologies.

A photograph is a graphical representation, just like a space-time diagram is. The fact that you're in the picture proves you were there. It is the same you in the picture from yesterday as the one from today. This does not imply the duplication that you seem to be obsessed with. It is the same you, yesterday, today and tomorrow. But at different points in time ! It is also as much 'proof' of the past as you're going to get, just like memories are.