Let's try to define a "now", and see if we can do it.
So I'm standing in a field, and off in the distance I see a boy playing with his dog. He throws a ball, and the dog goes and gets it. While watching this scene I'm tossing a rock up and down in my hand. At some particular moment, I see the ball leave his hand and feel the rock leave my hand. So, at first I think "These two events were simultaneous."
But then I remember that the speed of light is not infinite, it took time for the light from the ball to reach my eyes. No problem, I can account for that: I just calculate how long it took the light from the ball to reach my eyes and note that the ball left his hand that long before the rock left mine. Say he is 100m away: the ball left his hand 100m/c seconds before the rock left my hand. Of course I also have to take account of the fact that it takes time for the signal from the nerves in my hand to reach my brain (and similarly for my eyes), but again that's just some simple calculations. This done, I can write down a coordinate system and show when various events happened with relation to each other. Some events will be simultaneous but separated by space, others will be separated by time, some, of course, will be separated by both space and time.
In this way, standing in that field, I can make a coordinate system for the universe and say when events happen relative to each other.
To The Navigator: does this sound like a good way of defining the "Universal Now" that you're talking about?
I think post #260 explains what I understand as 'universal now' alexi_drago.
There is the off-chance that the confusion might be centered on the use of the word 'universal' which ordinarily contradicts the theories of relativity because "there is no 'universal now'" in relation to those theories.
However, that is quite generous of me because there has been enough said which should dispel any such confusion, and the gist of what I have said should really be quite easily understood.
I am not exactly sure as to why folk are continuously invoking the relativity theories as some kind of indisputable argument against what I am saying re;
The universe is One Thing (that's the 'uni' part of the word) and the assertion has never even subtly implied that there is anything incorrect about the theories of relativity.
The Universe is One Thing, and that thing should be able to be thus thought of as existing in a perpetual state of now-ness, irrespective of how the conscious parts of it (in this case human beings) might individually view it from within, as parts of it.
That is simply an extremely reasonable assertion.
Can it be falsified? Perhaps that is where the 'problem' can be sourced?
It is a claim that at any specific instant, the universe is in a specific state. In the next instant, it is in another specific state. There is no claim that the entire state can be observed, merely that it is. No observation, no frames of reference.
Wanting something to be possible and making something possible are two different things. If you want to make time-travel possible you have to address it using known physics since it the only tools we happen to have that work. Teleportation would be cool, but right now science and physics have given me a pickup truck.
I am sure that there are physicists out there working on time-travel as a mental exercise, but they are using Relativity in their work instead of pretending it isn't a factor.
When I write time-travel it breaks down to two options:
I explain how my time machine works.
I don't explain how it works.
Not explaining is the easy way to go because the story is about going back/forward in time and the adventure. Explaining the time machine requires hitting the books, finding abstract theories, and then figuring out a way to put them into motion (you know, who would have the brain-trust, the lab, the equipment, the money, etc). And in the end all I'm doing is dressing up the story for the handful of people who work in that branch of physics just to make them happy that I bothered to at least read up on the subject.
As a fiction writer I can play with all kinds of concepts, but if I'm going to drag them onto this board it would be to sit back and learn a few things to make my concept a little more solid for my story.
It's not real. I don't know how many ways to say it. It's a logical construct. You, me, they, it, no one can perceive the universe in it's entirety for any instant or "now." But we can imagine it, and use it to frame, among other things, how SR works.
Just like you understand what 1/3 is, but can't actually write it as a decimal. Or understand what pi is, yet can't write it out.
Again, imagine two stars explode at the same instant 10,000 LY apart. Got it? Great. No observer can observe what you just imagined. Yet, you can use that image to describe how observations of those two events can differ... Just like your wiki link does.
There's a lot of misunderstanding, even in this thread that the concept of ordering of events in relativity has to do with the time it takes light to reach you. While the time of flight of light is important, it's the constantsy of the speed of light that is the crucial element. If you do nothing else, watch this cheesily animated video:
You might need to watch it a few times or ask questions. That's ok. But the important question to ask is how to determine if the two events happen at the same time. At what velocity relative to the train do you make the "universal now" determination? And remember, that for a small thing like a train, the difference in event times is measured in nanoseconds, for something the scale of a galaxy, small changes in velocity, like, the speed of riding a bicycle, will shift this to years.
I understand the basics of observers at different points etc - I explained that this in itself didn;t appear to say that the universe wasn't one thing, I am told that time exists as a dimension of space, so since spacetime is where the universe exists, and since the universe is one thing, then the universe should thus be in a constant state of perpetual now regardless of where in the universe anyone (or anything) is.
It's not the different points that matter, it's the different velocities. When we ask what is happening somewhere else in space right now, we are taking the concept of spacetime and breaking it down into separate components of space and time. When we do this, we take into account our current reference frame.
Yes, I realize that SR goes completely against common sense and intuition. Can you approach this with an open mind? Is that something you are able to do? If you don't want to examine SR closely, then you'll just need to take people's word for it.
Imagine space and time as separate independent dimensions. Each moment in time is a flat plane and if we add a time dimension, it stacks the planes into a giant cube. Each slice you take out of the cube is a moment in time. It's the view of the universe that has stuck with us for a very long time. All our experiments tell us that this view is wrong. Instead, the slice you take depends on your relative velocity. Additionally, a cube is just a conceptualization that can lead to the idea that there can be a preferred slice and progressively steeper slices. The math is more complicated and from any given slice, it's the other slices that are progressively steeper.
That is logical yes? Yet I am continually told it is not so and when I ask why that is not so, I am told it is not so because those within the universe observe it differently.
You are getting caught up in the word observer. It's just shorthand that gets used for an inertial frame of reference. It isn't how someone observes the universe, it's the ground truth of the universe.
Wow! Solid! Not.
Why? Because it doesn't matter about those within the universe - they are PART of that one thing, and their position within it, while not the same as anyone else's position within it, (and thus relativity theories) this in itself does not mean that all time is in a perpetual state of now and thus the universe is - as one complete thing - is in a perpetual state of now and all the objects (not the consciousness of the objects) that together make up the universe are simultaneous in relation to that now...
If you want to observe the universe from the outside, how far away is it? Can you measure how far it is from you? Similarly, which point within the universe are you closest to? You can't measure these things because outside the universe necessarily means outside of space. You can't form distance relationships outside of space. This question is actually more complicated than the above since space and time in our universe aren't separate independent entities but a combined spacetime. Similarly, you can't form time relationships. From outside the universe, the universe just exists.
Well...since space and time are spacetime - indiscernible from each other (other than subjectively - through the existence of conscious being within it) then an 'instant' is really just a form of measure related to those conscious beings.
The 'moment' can be see as ongoing and indiscernible from the Big Bang on, in relation to the event of the universe.
Like an explosion, the whole thing is seen as one thing. It is not necessary to define the parts of it in a slow motion instant by instant freeze-frame manner. The whole thing (even in relation to those moments) is happening at once.
If you have no way of defining what two events are occurring at the same time, I don't really see how you can say anything about a "universal now". So you are going to need some definition.
I think the one I offered is the most straightforward (and it's actually how it's done in relativity), but if you have some other way of ordering events, please explain it.
There's no problem getting two observers to agree about a particular event in spacetime.
You can always set the time axis of two reference frames t and t1 at zero at some event. The problem is that they won't label a later event as having the same elapsed time from zero. And other events seen to be occurring at t=0 will be occurring at t1 = some other value.
Well...since space and time are spacetime - indiscernible from each other (other than subjectively - through the existence of conscious being within it) then an 'instant' is really just a form of measure related to those conscious beings.
The 'moment' can be see as ongoing and indiscernible from the Big Bang on, in relation to the event of the universe.
Like an explosion, the whole thing is seen as one thing. It is not necessary to define the parts of it in a slow motion instant by instant freeze-frame manner. The whole thing (even in relation to those moments) is happening at once.
That depends on the nature of the universe, for there to be a universal now there has to be a universal rest frame of reference, the universal now that you are talking of would be a snapshot of it.
There is no such thing in relativity as universal rest but there is no conflict, any such frame of reference is seen to be no different from any other frame of reference in relativity, there is nothing special about it and it is no more right or wrong than any other frame of reference and it may or may not exist.
It's not real. I don't know how many ways to say it. It's a logical construct. You, me, they, it, no one can perceive the universe in it's entirety for any instant or "now." But we can imagine it, and use it to frame, among other things, how SR works.
Just like you understand what 1/3 is, but can't actually write it as a decimal. Or understand what pi is, yet can't write it out.
Well, if it is not real, then what is its relevance to our universe? All kinds of logical constructs or abstract ideas can be conceived of or imagined, but that doesn't mean they are applicable to reality. The nature of reality sets bounds to what is possible. I can imagine the concept of a universal restframe or an observer outside of our universe or the smell of purple. But none of them are part of reality.
For those lurking in this thread who find the topic interesting, I'd like to recommend this series of lectures by Leonard Susskind on special relativity. It's designed for the layman, but goes relatively in depth. It's very understandable, but still goes further than most of the content you'll find on the topic. And I think it will clear up a great deal of the confusion that's on display in the last 7 pages:
What - in your opinion is 'the nature of the universe"?
for there to be a universal now there has to be a universal rest frame of reference, the universal now that you are talking of would be a snapshot of it.
For the umpteenth time, it is not about the internal individual beings of consciousnesses point of view. They too are part of the nature of the universe, not the ones who get to say how the universe is as an holistic thing...and that being. "no it isn't" It sure is if the individual can place his position within it as irrelevant to that question and subsequent answer.
Obviously the universe has to be something as that holistic thing and in that one simply has to lay aside the theories of relativity as some kind of principle which explains the concept of universal now in terms of that whole universe. Those theories ONLY deal with the fact that individuals have subjective reference in relation to the whole, from within it. These are not in themselves wrong and should not in themselves be used as a measure of right or wrong in relation to the overall universe and its most obvious state of perpetual nowness ,moment to moment - undivided.
Address that. Because no one is arguing ToR is wrong. It has nothing to do with the idea of universal now. It is all about how individual perceive the universe from within the universe.
Saying that because no one can see the universe from outside of it, is no argument because we see enough of it to get the gist. It is one thing doing one thing, not a series of disconnected unrelated moments.
What - in your opinion is 'the nature of the universe"?
For the umpteenth time, it is not about the internal individual beings of consciousnesses point of view. They too are part of the nature of the universe, not the ones who get to say how the universe is as an holistic thing...and that being. "no it isn't" It sure is if the individual can place his position within it as irrelevant to that question and subsequent answer.
Obviously the universe has to be something as that holistic thing and in that one simply has to lay aside the theories of relativity as some kind of principle which explains the concept of universal now in terms of that whole universe. Those theories ONLY deal with the fact that individuals have subjective reference in relation to the whole, from within it. These are not in themselves wrong and should not in themselves be used as a measure of right or wrong in relation to the overall universe and its most obvious state of perpetual nowness ,moment to moment - undivided.
Address that. Because no one is arguing ToR is wrong. It has nothing to do with the idea of universal now. It is all about how individual perceive the universe from within the universe.
Saying that because no one can see the universe from outside of it, is no argument because we see enough of it to get the gist. It is one thing doing one thing, not a series of disconnected unrelated moments.
I mean if something was travelling fast enough in relation to the rest of the universe, would its "now" look blurry?
Could it be travelling so fast that it kept pace with the "universal now" as it moved from past to future? If so, would that be the same as remaining static in time?
What - in your opinion is 'the nature of the universe"?
For the umpteenth time, it is not about the internal individual beings of consciousnesses point of view. They too are part of the nature of the universe, not the ones who get to say how the universe is as an holistic thing...and that being. "no it isn't" It sure is if the individual can place his position within it as irrelevant to that question and subsequent answer.
Obviously the universe has to be something as that holistic thing and in that one simply has to lay aside the theories of relativity as some kind of principle which explains the concept of universal now in terms of that whole universe. Those theories ONLY deal with the fact that individuals have subjective reference in relation to the whole, from within it. These are not in themselves wrong and should not in themselves be used as a measure of right or wrong in relation to the overall universe and its most obvious state of perpetual nowness ,moment to moment - undivided.
Address that. Because no one is arguing ToR is wrong. It has nothing to do with the idea of universal now. It is all about how individual perceive the universe from within the universe.
Saying that because no one can see the universe from outside of it, is no argument because we see enough of it to get the gist. It is one thing doing one thing, not a series of disconnected unrelated moments.
No, the theory of relativity makes no reference to beings of consciousness or subjective experience. It applies equally to all matter and energy, neutron stars or Wayne Netwon.
Asking the question of "what is happening right now" in relation to the whole universe is akin to asking which way is up in relation to the whole universe. Can you imagine arguing with someone about a universal up, and they keep insisting that up is a completely valid concept and they totally understand what up is and means and you could just accept their premise that there is a universal up.
BTW, check out a Penrose diagram for a black hole sometime. You have two regions of space for which it actually isn't possible no matter what angle you use to draw a line between what is happening "now" in the universe and what is happening "now" in the singularity.
Address that. Because no one is arguing ToR is wrong. It has nothing to do with the idea of universal now. It is all about how individual perceive the universe from within the universe.
The problem in a nutshell: according to relativity it's possible to order events A,B,C as occurring at the same time, OR as occurring A then B then C, OR as occurring in the order C, then B, then A. And the choice of which ordering you choose is dependent upon an arbitrary choice of reference frame.
Given the above, how do you square your idea that there is a universal "now" with the fact that the ordering of distant events is arbitrary?
What is "now" if not the moment in which things are happening, and what is a "universal now" if not the moment in which events everywhere in the universe are happening?
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