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Yes well they are actually related, although in different ways. Special Relativity relates to 'object in comparison to...', whereas General Relativity relates to 'object is not at rest as it is accelerating, when in a gravity field'.

So imagine a 'photonic clock', ie, 2 mirrors locked in place with a photon bouncing between them. By moving the clock, the photon will need to 'travel' a longer distance and the effect is:
- Under Special Relativity: if you are inside the clock, you notice no difference. If you are outside the clock moving at a different speed, looking at it, it will tick at a dilated rate because the photon will still travel from your point of view at the same speed, so the 'ticking' will be slower.
- If it accelerates, Special Relativity still occurs but at the same rate as the new speed. The photon will begin it's journey as normal in the clock from one of the mirrors, but by the time it gets to the other mirror, the clock has accelerated and thus the distance is larger. So, in regards to Special Relativity, there is no difference between velocity and acceleration. In your example above, if you stop accelerating, your dilation will now remain the same from then on, relative to someone else at a different speed.

Now consider the clock also is affected by General Relativity, if it is in a gravitational field (which all objects in the universe actually is). This is an additional effect, so you could say both forms of time dilation exist at the same time on the clock. But there are some differences:
- The clock is inside a gravitation field, and time elapses differently in the space around mass. This is not a function of the clock's velocity, but rather its location close to mass. Yes, it is experiencing 'acceleration' if it is close to a mass, however to clarify my simplistic post above it is not actually due to acceleration (the acceleration is the manifestation) but more accurately its 'gravitational potential'. So if the clock is on a planet, it looks like it is at rest, however it has 'gravitational potential' so if a hole suddenly appears under it and it starts to fall, this only manifests as acceleration.
- It is this 'potential' that causes the time dilation, different to special relativity's 'velocity'.
- I have omitted the obvious next step here, which is to do with 'spacetime', worthy perhaps of another thread. This explains why dilation would occur in the middle of the planet too, which theoretically there is no 'acceleration' because mass is all around you, yet the dilation would be the strongest here because that is where the field is the strongest.

SO, there are some key differences between SR and GR dilation:
- SR dilation is dependant on someone's viewpoint traveling at a different speed to yours.
- GR dilation is dependant on if someone is closer to mass.
- The difference means that if we all had clocks, in SR, our clocks would be seen as slower by each other, as we are moving away 'from each other'.
- Whereas the GR effect (which is in addition to SR), our clocks are moving at different rates by each if we are in different areas of Gravitational Potential (distance from mass) so this means a clock in orbit, as seen by a clock on the planet, could be faster, and a clock on the planet, as seen by a clock out in orbit, would be slower. This is a different result to SR where both would be slower as seen by each other.

I do agree that the concepts of special and general relativity are hard to grasp. To answer your question we need to explore:

• The nature of ‘speed’ (which relates distance with time). It is as simple as it sounds - how fast something goes over time.
• The nature of 'gravity' - not in that it is a force, but it's effect of accelerating objects together
• The concept of relativity and how it relates to gravity

So let's look at the concepts of relativity first. There was substantial confusion century-before-last as to how observational data was not lining up with theories at the time in relation to magnetic fields and classical mechanics. This distilled down essentially to two observable, seemingly (note) contradictory facts:
- light was measured as being a constant speed no matter where measured, or how fast measurements were 'made'
- otherwise 'classical' motion is indistinguishable no matter where, or how fast you are. In other words it makes sense doesn't it that a ball thrown while in a rocket is expected to behave predictably the same as if I was on the ground and threw a ball.

So how can both be true, if the speed of light from a torch on a rocket is measured the same if I am on a rocket, yet when I observe that same light looking at the rocket it should also be the same speed? Previous logic stated that it should be different speeds when measured from different velocities, but they were the same speed. This was the conundrum (simply put - there was a lot of stuff about electric fields and so on, but don't need to get into detail here).

Einstein reconciled these in special relativity, by saying both are true, because in essence observations were that that they were.
He simply then started to think: if they were both true, what else would be true? The difference is really in concepts of time, velocity and distance. So if the speed is of light is the same, it follows on that time must change to accommodate this truth. The rocket must be experiencing slower time to ensure that the speed of the light from the torch is the right speed when measured by someone on the ground. Hence, time and distance dilation occurs when objects are accelerating or decelerating.

Now: general relativity. Einstein had the same truths about gravity. He was likely wondering what gravity is, as concepts of ‘ground’ is also not really defined. Newton said gravity was just a ‘force’ between two masses, however Einstein was dissatisfied with this. If motion and acceleration is relativistic, why not acceleration due to gravity? Surely there shouldn’t be two forms of acceleration out there in the universe…

Hence two postulates for general relativity:
- no matter where you are or how fast you are, special relativity holds true
- including on a planet - where you are experiencing gravity. Ie. there is no difference between gravity and accelerating. Eg. if you are in a rocket, it is the same as if you were on a planet, you are experiencing the same special relativity effects.

So given these two factors - it holds that when you experience gravity it is the same as if you were in a rocket, you experience time and distance dilation as per the previous explanation of special relativity.

NOW THE IMPLICATIONS: Space becomes very weird (or rather just more complicated). Time dilation and distance dilation occur in relation to mass, not just if they were accelerating on rockets. This means light speed from a torch on a rocket is the same speed as measured from a stationary space station (meaning the rocket experiences time dilation) is the same effect as a torch on a planet also (meaning the location on the planet is experiencing time dilation).

This has matched observations, mainly Mercury, which Einstein proved was experiencing slower time close to the sun than when it was further from it, effectively proving the theory of General Relativity.

There is a lot of maths here that is omitted, and this is ‘thought experiment’ realm only, but is the basic principle - which is acceleration causes time dilation (because light is the same speed no matter where measured from), and gravitational acceleration is the same as normal linear acceleration.

Now another aspect of your question of 'why' relativity is true is more philosophical - and calls into question 'why' behaviours we observe are like this and hence the investigations of black holes and so on which push this theory to the limit - and there are still many mysteries to be solved...

Of almost all the concepts Isaac mentions I found the Self-replicating Machine episode the most tantalising. Can we actually make one?

And it got me thinking, how do you create Mega-Structures, space colonies, mass-produced mirrors or spacescrapers? You need to create a machine to build it for you, but not just any machine: a machine that makes the machine to make it for you.

Or a machine that makes the machine that then makes another in order to make a machine to make it for you. (You get the picture)

So this thread I thought we could jot down ideas on the challenges involved, and any solutions you can think of. For instance I would imagine the following problems, just starting with the basics using today's technology:
- how do you make a machine that makes another one? A 3D printer is the only solution I can think of at the moment. It is conceivable to print one using another.
- however complexity in current 3D printers is rudimentary. They use single pre-made materials and are assembled by hand. We need one that can be printed simply.
- and printing electronics is really hard, so your machine cannot 'think' unless it's possible. In order to print electronics you need materials that need mining and refinement processes that are hard to create and difficult to assemble. So perhaps you have a 'brain' like a central computer, that is manufactured using current-day methods, that 'transmits' instructions simply to 3D printed modules. These modules don't need to think then, they just move and perform tasks.
- they need power. However this could be centralised as well similar to electronics.
- The modules can assemble more modules using an easily workable material - what material I am not sure of, but it needs to be commonly found, easily configurable using only basic gathering and simple bonding techniques. Any material needed can be gathered by gathering modules, heated by heating modules, crushed by crushing modules, all of which must be able to made by the original material.

Which then presents the first question and wall to the concept - what material can be used for the above purpose? Does anyone have any ideas? Also feel free to post other challenges/solutions you could think of too.

I know this forum is yet to find its feet on what is and isn't allowed so I thought perhaps I'll post here and if mods want to move it elsewhere that's fine too.

I just finished seeing Orville's Identity part 2. For those that don't know the Orville, it is essentially now the replacement for what Star Trek used to be. BTW- spoiler alert.

Identity 1 was a great episode, for many reasons. But the main one for me was the questions raised about our tendency to readily Anthropomorphise objects. Isaac, the ship's robot, was being seen by all the human (and non-human) crew as a person, and his blank features seemed to accentuate the fact that we can write any impression of what we think he is on his face.

The episode was great because after know Isaac for so long, where we see crew members treat him as a person, Claire even falls in love with him, in the end he was programmed to betray all in a reasonably logical motive to eliminate all biological life, and it called into question all our thoughts up to that point - Am I guilty of thinking Isaac was a person, entitled to emotion and compassion? What is he, if not what we thought he was? I found myself rerunning old episodes to observe Isaac's interaction with the crew, and suddenly all was cast in a sinister light. Yes he commonly viewed himself as superior intelligence (the crew laughed and assumed it was Vanity) or commented on the failings of his fellow officers (some call it Pride) but in the end these were emotions we projected on to him, he was always what I thought him to be, and I don't know how else to think of him.

Superman (the old 1978 film) was a great movie because it explored a similar theme - this time from Lois Lane's point of view: She fell in love with... what? There was a scene in the middle of the movie where we are suddenly privy to her inner thoughts, yearning or hoping he was what she thought he was (or that he would notice her). This was pivotal as we suddenly realised then that the movie was not about Superman at all (even though he is the star) but actually about what Lois Lane's reality was. It calls into focus the bigger question we all face: Do we really know what is real? When we love someone, what do we love? Are we actually seeing what our minds (and heart) wants to see, and it is not possible to see any other way?

Identity 2 resolved the issues opened so intriguingly in a rather perfunctory manner - I did not think it nearly as successful as Identity 1 because I believe the question cannot be answered as it goes right to the heart of being ourselves in the universe, and seeing it as a microcosm of ourself. In fact, the solution in Identity 2 was that the robots were angry at being mistreated by their makers, however this sidesteps the issue and actually applies an emotion (hate) to logic, which is destroying exactly the point Identity 1 was trying to make. Space battle and all, I almost wanted Isaac to continue to be emotionless, as well as his fellow robots, to explore this further (but I suppose the 'TV Show' can only go so far before it must resort to expected tropes).

So - this thread is mainly then about then: Consciousness and being in this body and viewing the universe. I am here in this body - can I truly know someone? Can you? Does it make it impossible to view the universe from a single point of view (a human point of view) meaning we cannot truly know someone, or something, as we are viewing it only through our eyes, and the very act of observation must be done in the context of human meaning (for example, emotion)? Ie, Isaac is a robot, no more than a bunch of atoms, yet we look at him with meaning, hope, fear, expectation, all the emotions we have - we 'see' him, whether real or not - and do you think you could view him in any other way?

In this thread, post your greatest dream.

I dream: The universe is right now bustling with technological life, that it is crowded, they all love talking to each other and meeting up on crowded stations, ships and planets, it has been for some time, and for some reason however unfathomable we just can't see them.

What's your dream?

This is the very first thread I have posted - I'm a new public user who just drifted in with the wind.