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Time is a dimension, but not like space
- nyc111 2y agoI would really appreciate if people writing these types of articles first give rigorous and unique definitions of space and time.
- blackbear_ 2y agoSomething like (from Wikipedia): > In the presence of gravity spacetime is described by a curved 4-dimensional manifold for which the tangent space to any point is a 4-dimensional Minkowski space. Perhaps? A good way to lose 99% of the readers before the end of the first sentence.
- mise_en_place 2y agoJust represent it in a 4x4 multidimensional array that corresponds to the metric tensor.
- hn_throwaway_99 2y agoYes, that will really pull in the laymen...
- nvader 2y agoReminds me of the mathematician who was asked how he mentally visualizes a 4 dimensional space. "I simply imagine an n-dimensional space, and then set n to 4"
- homebrewer 2y ago>>> After Hilbert was told that a student in his class had dropped mathematics in order to become a poet, he is reported to have said "Good--he did not have enough imagination to become a mathematician" https://scienceworld.wolfram.com/biography/Hilbert.html https://scienceworld.wolfram.com/biography/Hilbert.html
- golly_ned 2y agoReminds me of Geoffrey Hinton who, when asked how to imagine a 14-dimensional space, said: “imagine a 3-dimensional space, and say ‘fourteen’ very loudly”
- esperent 2y agoThis is great, can't believe I haven't heard it before.
- deleted 2y ago[deleted]
- zbobet2012 2y agoI'm a huge fan of providing laymen explanations. And at some point if you _actually_ want to understand you have to stop using those and pickup and understand the math. http://therisingsea.org/post/mast30026/ http://therisingsea.org/post/mast30026/ Has a good introduction to space, and the notion of a manifold, and what a Minkowski space is.
- verzali 2y agoOk, but almost nobody is going to read an article that requires you to work through 21 lectures, 9 tutorials, and 3 assignments first. It'd be great if they did, and it'd be nice to give the link for interested people, but otherwise it is just making the subject inaccessible to almost everyone.
- slashdave 2y agoThat's in the article on Minkowski space. It's actually a good summary, with a hyperlink to manifold. Here's the introduction to the "spacetime" page: > In physics, spacetime, also called the space-time continuum, is a mathematical model that fuses the three dimensions of space and the one dimension of time into a single four-dimensional continuum. Spacetime diagrams are useful in visualizing and understanding relativistic effects, such as how different observers perceive where and when events occur.
- whatshisface 2y agoTime: a separation between individual events that can be crossed by cause and effect. Space: a separation between individual events that cannot be crossed by cause and effect. "Individual event" is meant in the familiar sense, like a "bang" from a gun, or your birthday party.
- HappMacDonald 2y agoThat's a solid burn, suggesting that nobody else came to their party
- ziofill 2y agoMy favourite explanation (which IIRC is in a book by Brian Greene) is that you can think that everything always moves at the speed of light in a 4D spacetime. That way, if you stand still, you're moving only along time, and as you tilt your velocity vector more and more toward the space dimensions you have to travel more slowly along the time dimension. At the limit you are moving at the speed of light along some space axis and technically your time is "frozen".
- at_a_remove 2y agoOr as I tell people, kidding on the square, we're trapped in a time machine hurtling us into the future at the rate of one minute every sixty seconds! It is important you say that last bit in a panicked, breathless voice. My God, that means every three hundred sixty-five days or so, we'll have gone forward a year!
- deleted 2y ago[deleted]
- colordrops 2y agoBut then it gets weird and the time axis changes scale relative to other elements in space.
- ndsipa_pomu 2y agoFor an observer, maybe
- colordrops 2y agoThere is no absolute frame.
- Ringz 2y agoThee is no „Stillstand“, you can’t stand still relative to anything in the universe.
- DiscourseFan 2y agoAs per Kant: Time: inner sense, intuition of continuity, unity Space: outer sense, intuition of objects Its a bit more complex but that’s a basic summary from the guy who came up with the “space and time” thing. Read the “Transcendental Aesthetic” in the Critique of Pure Reason for more.
- User23 2y agoMy understanding from Einstein’s book Relativity is that the four dimensions of general relativistic spacetime do not correspond to any one of the time or space dimensions of special relativity or classical physics. It’s a great read, and short too. He explains it much better than I could.
- nyc111 2y ago"This is the underlying reason why, when you move at speeds that approach the speed of light, you start to experience phenomena such as time dilation and length contraction:" This is not even possible in pulp science fiction. In order to be able to move with the speed of light you need to transform yourself into a photon. Only a photon can move with the speed of light. Saying "close to the speed of light" changes nothing. You need to be light to move with the speed close to the speed of light. Macroscopic objects cannot move with speeds approaching light speed.
- deleted 2y ago[deleted]
- klodolph 2y ago“Close to the speed of light” means, like, 99% of the speed of light. You can even see the speeds listed on the graphs, which are given as a fraction of c.
- nyc111 2y ago"'Close to the speed of light' means, like, 99% of the speed of light" So, you are saying that it is possible to accelerate human body to 99% of speed of light without transforming the body into a massless particle?
- tsimionescu 2y agoYes. It will never be possible to get to 100%, but I principle anything below that is possible. Not just 99%, but 99.99999999% or however many you want. Of course, it's not actually feasible, you would need galaxies worth of energy to do so. But for something like 10% or even 50% of the speed of light, it's not even that implausible.
- etcd 2y agoWhat is our current speed?
- at_a_remove 2y agoI only got my undergrad in physics, but I think there is something there to be mined between time as a dimension and the second law of thermodynamics. Why this one? First, I will render a quote which never failed to amuse me: "The law that entropy always increases holds, I think, the supreme position among the laws of Nature. If someone points out to you that your pet theory of the universe is in disagreement with Maxwell's equations -- then so much the worse for Maxwell's equations. If it is found to be contradicted by observation -- well, these experimentalists do bungle things sometimes. But if your theory is found to be against the Second Law of Thermodynamics I can give you no hope; there is nothing for it to collapse in deepest humiliation." (Eddington) Why such honor? For one, in statistical physics, you can more or less derive the second law of thermodynamics, from scratch. No need for observation. It's just there the same way the quadratic equation is. Somewhere I have a cheap Dover reprint which contains a relatively easy to follow construction of the second law. It's the math. You can measure things badly, you can find one phenomenon creating the appearance of another, but you cannot fool The Math. And so the statistical physics you can get from just math gives you this arrow of time, flying only one way, just as we see from spacetime. To me, and again, I only got a few grad courses under my belt in it, this suggests not just a deep connection between entropy and spacetime, but the inevitability of it from the basic math (really, a talented high schooler could be coached through it) means that there is something about large (for n = ?) numbers of particles losing the reversibility which is so often present in particle interactions where n is smaller. What gives there? How do we go from this "trend" emerging to it being a property of spacetime even if no particles are sitting in said spacetime. Not that I would have dared write the great Wheeler, but I have wondered if his "geon" concept would have fit in with this sort of thing. It seems so fundamental. One can imagine a universe with a different number of un-unified forces, or gravity dropping as the inverse-cube, or varying physical constants, but the math is still the same in these universes and it then suggests that there's no, uh, room for an option wherein the time facet of spacetime is anything but an arrow flying forever on towards entropy in its many masks. A great task, or perhaps a very alluring windmill, for someone younger and brighter than I.
- mkleczek 2y agoThe older I am (and I am at my 50s) the more I have this intuition that entropy is a fundamental force driving not only physical phenomena but also social interactions, economy etc. Formalising this intuition is another story though...
- heed 2y agoAlso consider the speed of light is also the speed of causality. If there was no such limit it means it would be possible for effects to precede causes which would lead to a very different kind of universe!
- wruza 2y agoWouldn’t it just happen instantly and settle on some fixed point?
- Dylan16807 2y agoThere's a lot of ways to implement that and most of them aren't a problem. For example: If there isn't a speed of light, how fast does light go? If it's variable but not instant, then depending on the details causality violations could still be very rare or impossible. If it's instant, then how do we define instant for different observers? I feel like relativity-style calculations don't really work. If "instant" is agreed upon by all observers then we won't have causality issues.
- dcow 2y agoCould you even measure or experience variable speed causality? Or, it doesn’t matter what made up constant you assign the speed of causality. You’re just bits on a page and you only perceive anything as the clock cycles.
- ben_w 2y agoI've heard it claimed that we can only measure the round-trip speed of light, not the one-way speed of light, because the maths says that reality would look identical if it was 0.5c in the x+ direction and ∞ in the x- direction. I find this hard to stomach, but I'm going to trust it also applies to e.g. magnetism being Lorenz transformed electric fields, because relativity violates "common sense" all over the place and reality doesn't care about my stomach. https://www.youtube.com/watch?app=desktop&v=pTn6Ewhb27k&themeRefresh=1 https://www.youtube.com/watch?app=desktop&v=pTn6Ewhb27k&them...
- pyinstallwoes 2y agoThe ontological dissonance in that title is spectacularly simulacrum level 4.
- stogot 2y agoI see a variety of discussions of time with different views. Is there a good summary or journal review article?
- mellosouls 2y agoThis is the sort of question I think is useful to explore with ChatGPT et al, and of course you can ask for links. In the meantime, Stanford and IEP are always good for this sort of thing (including as a background for conversing with the former): https://plato.stanford.edu/entries/time/ https://plato.stanford.edu/entries/time/ https://iep.utm.edu/time/ https://iep.utm.edu/time/
- tightbookkeeper 2y agoYou’re just going to get philosophizing with scientific language. Beyond the mathematical model used for a particular physics question, there just isn’t much consensus.
- roughly 2y agoIt won’t necessarily convey all the different views, but The Order of Time by Carlo Roveli is an absolutely beautiful walk through the various interpretations of time down to the quantum level. The nature of time is not fully understood and Roveli understandably (and openly) has and endorses his own view here, but he covers the ground upon which there’s consensus quite well.
- IgorPartola 2y agoIf I understand correctly, we experience time at nearly the speed of light. What I mean by that is that any particle’s 4 dimensional velocity vector has the magnitude of c which means that if it is mostly at rest in space then time has to be the major contributing factor but the magnitude of the vector. On the other hand something like a photon experiences to time at all as it moves through the 3 space dimensions at a total of c.
- crazydoggers 2y agoI believe that’s an accurate model, with the caveat that it’s all relative. There’s no universal reference frame. So for the photon and his pal photons, they experience time while you (in your reference frame sitting still) are the one moving at the speed of light and not moving through time. Edit: See below, the photon doesn’t have its own reference frame so they still don’t experience time.
- Filligree 2y agoPhotons absolutely do not experience time. The spacetime interval of any photon is always zero, and the spacetime interval tells you how much time any particle experiences. Note that it’s invariant.
- crazydoggers 2y agoYes you’re right.. the photon has no reference frame of its own then. So then that would just apply to massive objects with their own reference frames.
- aszantu 2y agoI still don't get it, photon comes into existence and then slams into a thing for us to notice the existence. Between the being born and slamming into something time passes, no?
- hhejrkrn 2y agoFor everything around it .. But not for the photon?
- pelorat 2y agoCorrect, it's a mathematical dimension.
- quantadev 2y agoOne Speculative Theory of Spacetime: Our universe is a 3D Manifold in a higher dimensional space. All event horizons have a "surface normal" (orthogonality) direction at any point. For example a conventional Black Hole (2D one) has an event horizon that is a 2D surface. That is, for a flatland creature living on that EH it takes two coordinates to define a location, but these flatlanders would experience "time" as the "growth" of the EH (like when more mass falls into it, and the EH grows), and the direction is "outward" (perpendicular to EH surface) Now here's the interesting part: Event Horizons come in all dimensions. Our "Universe" is a 3D EH, but of course at any point in space there's a unique "rate of time" and a common "direction" of time, which from a higher dimensional space perspective is simply the "orthogonal direction" to all our space directions. (Time orthogonal to Space [i.e. Minkowski]). As matter falls into our "Universe", that moves time forward for us. But our universe itself consists of all the "points" (Quantum Decoherence Points) which are co-located on a 3D manifold embedded in a higher dimensional space. This means the Big Bang has things exactly "inverted", and is wrong. Matter didn't "originate from inside". It's the opposite o that. Everything "fell in" from outside. The reason our universe is expanding and accelerating is because it's a black hole EH. Black Holes mainly just grow (excluding tunneling etc).
- MarcoZavala 2y ago[dead]
- threatripper 2y agoHas this been investigated in detail by physicists? Does it hold up in theory?
- quantadev 2y agoI think it's one of those things that borders on the unfalsifiable, similar to multiverse theory. I've had this concept for about a decade, but I did actually see a youtube video of a Cambridge (or some well known University for Physics) where a professor/researcher did present the idea, yes.
- nakedneuron 2y ago
- defanor 2y ago> Your motion through the x dimension in space, for example, is completely independent of your motion through the other two (y and z) spatial dimensions. If one considers motion at (or near) the speed of light, that speed would have to be shared among space dimensions, just as with the time dimension. So not that independent.
- 123pie123 2y agoi've never really 'properly' understood spacetime - can you expand on your comment? why would going v fast in the x direction affect y and z?
- ben_w 2y agoIf I am seen to go at [v_x, v_y, v_z] = [0.9, 0.9, 0.9]c, then I would be going at about 1.56c in the [1, 1, 1] direction, which is impossible.
- deleted 2y ago[deleted]
- nkrisc 2y agoThink of it as a maximum vector length. As one component of the vector nears the maximum length, the other components most reduce until the vector is aligned with only one axis and at the maximum length - the other components must all equal zero. That is - to my limited understanding - essentially why photons are “timeless”.
- geon 2y agoWe constantly move at the speed of light through space-time. If we start to move through space, we slow down through time. If we go full speed through space, like a photon, we will not experience time at all. So from the perspective of a photon, everything happens at the same time, from the big bang to the heat death.
- deleted 2y ago[deleted]
- glossybrown 2y agoHere’s something I’ve never understood; perhaps a more knowledgeable commenter can explain it to me. If I get in a spaceship and accelerate up to about 0.9c, then cruise for a while, then flip around and come home at the same speed, I will have experienced much less time than the people on Earth. But from my frame of reference, they were the ones going really fast, and I was sitting still. If all motion is relative, what makes me the one to experience less time?
- jiggawatts 2y agoThis is a well known paradox: https://en.wikipedia.org/wiki/Twin_paradox https://en.wikipedia.org/wiki/Twin_paradox TL;DR: The two scenarios are not symmetric, the person in the spaceship undergoes acceleration whereas the observer staying behind does not.
- axilmar 2y agoOf course the math check out, they are correct, but in my opinion, time is not a dimension, it's the 'refresh rate' of matter. To me, there are only 3 dimensions, that of space. That does not mean the relativity math is useless. On the contrary, what they describe is real and we can experimentally verify it. But that does not mean we can 'move' into time, as we 'move' into space. That's why time is not a dimension.
- scotty79 2y agoHow does your refresh rate time accounts for time slowing down for things moving fast (relative to you) regardless of spatial direction they are moving? Spacetime simplifies many things for example in that framing nothing is ever at rest or nothing ever travels at different speed. The speed of everything is the same, it's just that things spatially at rest have all their speed in the direction of time. Accelerating something in spatial direction is rotating (mathematically) their motion away from time direction, into some spatial direction. This requires energy so the time direction is lowest energy but to rotate it away from it you need to put in energy. If you want to rotate it to 45 deg you need infinite energy.
- lottin 2y agoThe refresh rate doesn't slow down, but the speed at which things change does, at high speeds.
- neurotypicalc 2y agoI don't believe refresh rate captures the transmission of time onto other objects it would only capture individual time, they have to sync up somehow and gravity affects it so its not just matter, its the impression of matter onto the fabric of space
- lottin 2y agoSpace has no 'fabric'. Space is not a physical entity, but a set of coordinates.
- 2y ago
- falcor84 2y ago"Time is an illusion. Lunchtime doubly so."
- hoseja 2y agoAs with all such articles, there is no real help with getting through the hurdle. Very surface-level, sounding like AI summary at times. Also, AFAICT, nobody has yet actually worked out spacetime with masses properly, right? Where masses influence and are influenced by space, each other and time, all at the same "time", in general? Edit: Looks like people are working on it? (for mergers of binary stars) https://arxiv.org/abs/2405.06035 https://arxiv.org/abs/2405.06035