RAD4921 said:
AnssiH said:
Well, the thing is that relativity strongly implies that time does not tick away but that future and the past exist all the time. So that's what I was talking about in the other thread.
I have heard people talking about how everything is happening at once. That is interesting. Do you know where I can ontain more information about this
RAD
Looks like Kvantti already posted some links.
Few words still; it would be wrong to say "everything is happening at once" because just the word "happening" implies motion. We should say "everything exists at once". May sound like splitting hair, but it's too easy to confuse the idea of motion to spacetime and I see people doing it far too regularly without realizing it.
And why relativity implies static spacetime is that it assumes simultaneity is not absolute but it is relative to your direction of motion (and by this assumption we can assert that the speed of light is the same to all observers). This is the basic building block of relativity and needs to be understood properly.
Thought experiment; let's say there is a spaceship approaching us at great speed. By assuming the light is approaching us at speed C, we can figure out what is the "real" moment when the spaceship is just passing Alpha Centauri, assuming it is moving at a steady speed. We decide to put up a signal beacon at the same moment.
Now, SR says the moment we put up the beacon and the moment the spaceship passes Alpha Centauri are not "really" simultaneous in any inertial frame but in our. When the spaceship receives a signal from our beacon, it can figure out when did the beacon go up, and assuming the speed of light to be C in its own inertial frame, it will conclude that the beacon went up much much earlier than when it was passing Alpha Centauri.
This means that when the spaceship had not yet even passed Alpha Centauri in your frame, in its own frame you had already put up the beacon long time ago;
your future had already happened I.e. your actions are deterministic since they have already happened from the point of view of many inertial frames. (Determinism is not problematic part though; it is not particularly hard to show that the idea about free-will is nonsensical anyway)
It also means that if the spaceship now accelerates (brakes) to the same direction of motion where you are, it will come to share the simultaneity with you. For example, if in its original frame you had put up the beacon three weeks before it reached Alpha Centauri, then when it brakes, the clocks and everything on Earth rewind back to the moment when you were just putting up the beacon.
But this doesn't really make sense as is, so if you assume simultaneity to really be relative, you will also feel strong need to assume reality is a spacetime where future and past actually exist all the time; that "time is just an illusion".
It would also mean that time exists as a real dimension in which all the events that ever happened and will ever happen are marked. And in this spacetime NOTHING could actually move. If you assume time "causes" motion, and you assume any motion in spacetime, you also need to assume a new time dimension which causes/describes the motion inside spacetime, and this leads to infinite regress. If you are not convinced of this, please think more.
So I hope now everybody have some idea about why relativity strongly suggests static spacetime.
And the reason I say "strongly" is that relativity doesn't allow for any direct observation of the relativity of simultaneity. We cannot actually see the clocks moving backwards or anything like that. Strictly speaking, what we can measure is that different objects move at different rates in different situations, and this doesn't actually require that future and past exists all the time; ALL the observable effects of relativity could work by universal notion of simultaneity, but to describe the reality this way would not be "geometrically simple" the way that SR is simple.
However, read on...
Doctordick said:
The problem here is that most all of you have made no real effort to understand what "time" is all about (and I include most all scientists in that category).
Spot on. And I had almost lost all hope already. I keep hearing these unthoughtful claims about how "motion could not exist without time" and all sorts of ideas that mix up the concepts of motion and time into incoherent whole, and it's just driving me insane...
"Motion could not exist without time" is simply invalid assertion. Of course it could exist without time; motion could be fundamental feature of nature! It is not in any sense "more likely" that time is what is fundamental instead of motion. One needs to understand how we understand the world. We create semantical assumptions and concepts about what we observe, and by observing motion, we can derive the semantical concept of time! When we say "It takes 60 seconds to boil water" we are saying "by the time the little hand on the clock has done full circle, the water is boiling". This is nothing but a comparison of TWO MOTIONS.
Just like in a universe with just one object there is no "speed" for the object to measure, so there is no "time" for it to measure. There is no backdrop called "empty space", this is a figment of imagination. Similarly, we cannot measure time itself. That's right,
time cannot be measured. We cannot claim that "time" moves at certain speed at all. If you feel the need to reply "I measure time with my wristwatch all the time", think more.
Few words about one particularly interesting case of "mixing up concepts incoherently". It is asserted that spacetime was created in the big bang 15 billion years ago (give or take some). If this sounds unproblematic idea, think more.
Imagine a 3D-block. Let's say this is the whole reality for 2 space dimensions and 1 time dimension. At the bottom parts we have the "past" and at the top the "future" (=entropy increases upwards).
When we imagine the moment when this spacetime is created, it would be immediately wrong to imagine that it starts to grow from the bottom; this growing would require motion to exist (instead of time). No, the creation event is just one "pop" and the whole thing comes to exist in a static sense, with the beginning, the middle and the end.
Except that even a concept of this "popping" event is something that makes sense only inside spacetime, not outside. We can only say something pops into existence if there is real motion and evolution to a system. When we say the spacetime was created 15 billion years ago, we are saying that at the bottom of the spacetime there is an event which caused the whole spacetime to "pop" into existence, including that "first" event itself. Think about this for a while. Is this very clever idea?
The original assertion was made by extrapolating the expansion of the universe backwards in time until you get to singularity. At that point you can imagine that the whole spacetime curls into a singularity, only this curling is also motion! You cannot say there existed a time when spacetime was curled into a singularity any more than you could say the spacetime is wiggling around.
This is just one instance that drives me crazy, and I'm almost certain this post will also trigger few replies from people who don't think I understand properly what it means that "spacetime didn't exist before big bang". Please... This is just elementary idea and the issue of time is much deeper than some vague idea about how nothing "is" before big bang.
Oh, and entropy, it's a neat idea and all, but it is becoming more and more difficult concept in my worldview, which is becoming increasingly darwinistic. Super-darwinism I could say. Self-organization does not agree very will with absolute (overall) entropy. Yes, dropping a rock on pavement will cause chaotic heat release, but things also fall into all sorts of stable patterns.
I'm thinking entropy and self-organization could both "really" exist, and that could be why there is a universe in motion but still stable; it could be that it will always stay stable, that there will always be chaotic things getting organized and organized things becoming chaotic. Maybe, just maybe... At any rate, self-organization seems like a good way to understand any system (including the brain).
Anyway, if the post I linked to didn't seem to make sense to you before, perhaps after thinking through this post it makes more sense;
https://www.physicsforums.com/showpost.php?p=1100575&postcount=130
(There is a larger issue with time and motion when you get to the philosophy of mind... If this issue does not exhaust you... think more :)