Rat avatar, yes I get that stuff about mass warping space-time and and that there is no objective time. I get the gist of SR as well. It’s the stuff about the future as described by eternalism that many seem to justify with the theories of relativity :
From Wikipedia on eternalism (philosophy of time):
Based on this description, seeing the alien invasion is not the “type of future” proposed by a block universe. It appears to be saying that my “local” future already exists and that my lifeline is a pre-determined worm crystallized in the fourth dimension.
It may help to consider the implications of that claim by thinking of yourself as a photon. You do not experience time at all,. There is no future or past, just a single point. Your own emission and absorption is a single event. How does that work within Wikipedia’s definition of eternalism?
I think that goes to the subjectivity of time, not evidence of a pre-determined future. I totally understand the subjectivity of time (i mean as much as a reasonably well-read layman can), I just don’t think the examples that people use to support the idea that the future already exists, like that Brian Greene video, really supports the case for eternalism as described above . It just supports that there is no objective now.
My opinion is that we need to be a bit more specific in our language. When someone refers to “a 4th-dimensional being”, what they mean is that (as you wrote), they “have freedom of movement in the 4th dimension”, i.e., that to them, there are four dimensions of space. – In which case, they experience time as the fifth dimension.
If so, then “today” IS a concept relevant to them, except that we cannot establish any sort of connection between what we perceive as “Wednesday” to any of their time periods.
(This might be the same as what Mangetout wrote, but in different words. Or different. I’m not sure. Just contributing to the conversation.)
But there is no fifth dimension that we know of. The idea that there is an n+1 dimension that is time won’t wash. After all, this 4 dimension being would start thinking about 5 dimension being that see its time dimension as a spatial dimension. And so on.
Time has different properties to the spatial ones, so it isn’t clear how you can keep this idea up. There are theories with many more dimensions, but none of them work with more than one time dimension. So whereas you might have beings that see more dimensions than we do, the idea they can treat time in the manner we do a spatial one is very difficult to make sense of.
I use an analogy to a reel of movie film. Imagine those people who live in the film, trapped in two spatial dimensions. To them, “now” means one particular frame of the film, while all the other frames are their past and their future. We who have three spatial dimensions can see all the frames at the same time.
Clearly, “time” is different for us and for them. Their past, present and future are all equally real to us. In fact, we are not able to point to any particular frame as being “now”.
For them, time is the third dimension, after the two spatial ones. For us, time is the fourth dimension, after the three spatial dimensions that we are so accustomed to. I cannot imagine how a fourth spatial dimension would look, but I find that this analogy makes it possible for me to understand how the fourth spatial dimension would work - and how time would be perceived there as a fifth dimension.
Brian Greene is amazingly good at explaining these things. One thing I don’t get though. If past, present and future all exist simultaneously isn’t that determinism, ie I have no choice in what I do because the future already exists and can’t be changed?
However you have done something curious with the time dimension on the film. It no longer behaves as time does. Actually the entire film no longer behaves like spacetime. For one, there is a preferred frame of reference. You.
But this 3D + time thing that is viewed like a film is embedding in the same space as the being is in, and in principle the being can move into our space. It can interact with our space - a lot like we might imagine interacting with beings in flatland. Which means it can change our future. If it can do this, our time dimension must still behave as one. Not as a 4th spatial one. Which might mean more than one time dimension. But that doesn’t work as far as we know.
It may be that there is a projection from 4D spacetime to 5D spacetime that allows the time dimension to somehow be sensibly converted - but I sort of doubt it. A being with 4 spatial dimensions will probably just share our 3 and out time as time, and have another property. More like flatland in our world.
IMO / AIUI time-like dimension(s) are fundamentally qualitatively different from space-like dimension(s). OTOH, Minkowski and the idea of 4D motion to explain time dilation, etc works well. As far as it goes. So far, so blindingly obvious.
Similar is not identical. Which means that we need to be very careful to not push their similarities beyond the breaking point. Which IMO happens as soon as folks posit beings or POVs able to view multiple points in time, move in time, time as a fixed block, etc.
A metaphor:
If we consider ordinary motion on the surface of our sphere, motion north/south is significantly different from motion east/west. Which in turn is significantly different from motion up/down. Each of these directions of motion have a lot in common. But not everything. As well, N/S & E/W have more in common with each other than they do with U/D.
The statement “North and Up are both dimensions, so all motion in them is equivalent” only takes you so far before it falls apart.
The whole debate here is that we really don’t know the edge of applicability of “time is a variant of a space-like dimension”. IMO the “future exists” POV is stretching the metaphor well past the breaking point. As such any reasoning following the rules of the metaphor may be logically valid (=internally consistent) but invalid vs. the real world.
Funny I don’t think he’s good at all. He seems like other popularizers that make the double-slit experiment seem spookier than it is by implying some conscious attempt by the universe to conceal the nature of light or that the collapse of the wave function is somehow different than any other particle if it’s observed by a human. In that video I think he’s trying to say that the world is deterministic and the future already exists, but I don’t think his example proves that at all.
But theoretically since the viewer of the second dimension film is one dimension higher, he can have an absolute frame of reference. He sees all of our space-time frozen. I’m not sure what you mean when you say this being can interact with our space. Do you mean we can interact with his?
I would think that a 4th dimensional being would exist outside our universe in a different space and see our universe as a super long spacetime football (big crunch) or bullhorn (big freeze). His fifth dimension is time. One dimension higher than any being is always a process of becoming. A point experiences moving along a line as time, a square perceives the cube as time, we perceive moving into the 4th dimension as time. One dimension lower than you is “space” and one dimension higher than you is always time. I should stop smoking weed.
I would say a frequent objection to the idea that relativity implies a so-called “block Universe” is that the physics of relativity, including the causal structure, rest in the relationships between events as defined by the metric structure of spacetime. A spacetime manifold is physically meaningless without this additional structure.
This sometimes comes up in time-travel fiction. Ordinary clock time is the fourth dimension, but the time-traveller’s subjective experiences are in a “higher” time – what Fritz Leiber called “The Big Time.”
I went back to 1963, “and then” I went back to 1066. That “and then” is the higher time.
Absolutely no evidence of it existing, and some strong mathematical reasons it shouldn’t exist. It leads to paradoxes. (As does time-travel in general, of course.)
No, you have it inside out. The present is the past, and the past is the future. They are all one, in the much same way that, through your genes, your are your ancestors and your descendants will be you. It makes no sense to separate time into these arbitrary divisions. They connect to each other seamlessly and are all defined by probabilities – ultimately, the past is not more certain than the future.
As the guru said to the hot dog vendor, “Make me one with everything.”
I’m rather surprised that this thread got to the second page without anyone referring to this classic work: Flatland: A Romance of Many Dimensions. The book is available from many sources, so that’s why this link goes instead to the Wikipedia page. Anyone who is interested in this thread really ought to try reading it. I first read it in junior high school (many decades ago) and I’m still entranced by it. The Wiki article points out that the book has a lot of social commentary, and my first reaction was to be bored and annoyed by that. But I must admit that it adds a level of realism to the characters, and helps me to empathize with them and feel their beliefs about their flat land.
In as much as there’s a notion of a ‘present moment’ in special relativity, both the aliens leaving and debating are in the present (that is, have the same time coordinate) of the moving or stationary observer. So the aliens leaving hasn’t already happened.
Also, of course you can play the game in both directions: to the alien fleet, the ‘present’ is a point to the future of both observers on Earth—i.e. to them, the meeting has already happened.
Yes but AFAIC, if an event has occurred in the past of anyone else’s time frame, then it can’t be rightly used as evidence of eternalism. Like I said I’m not doubting the relativity of time - I’m just doubting that SR predicts eternalism.