Time is a dimension, but not like space

https://bigthink.com/starts-with-a-bang/time-yes-dimension-not-like-space/

by belter • 2 years ago

173 198 2 years ago

nyc1115• 2 years ago

I would really appreciate if people writing these types of articles first give rigorous and unique definitions of space and time.

blackbear_• 2 years ago

Something 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• 2 years ago

Just represent it in a 4x4 multidimensional array that corresponds to the metric tensor.

zbobet2012• 2 years ago

I'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/

Has a good introduction to space, and the notion of a manifold, and what a Minkowski space is.

slashdave• 2 years ago

That'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• 2 years ago

Time: 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• 2 years ago

That's a solid burn, suggesting that nobody else came to their party

ziofill• 2 years ago

My 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_remove2• 2 years ago

Or 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!

colordrops2• 2 years ago

But then it gets weird and the time axis changes scale relative to other elements in space.

Ringz3• 2 years ago

Thee is no „Stillstand“, you can’t stand still relative to anything in the universe.

creata• 2 years ago

Some of the answers at https://physics.stackexchange.com/q/33840 explain why "everything always moves at the speed of light in a 4D spacetime" is a statement that, at best, has no content.

DiscourseFan• 2 years ago

As 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.

User232• 2 years ago

My 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.

ofrzeta• 2 years ago

Do you mean "Relativity: the special and general theory"?

User232• 2 years ago

Yes

nyc1115• 2 years 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.

klodolph• 2 years 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.

nyc1115• 2 years 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?

antonvs• 2 years ago

You might want to look up the word “approach” in a dictionary.

Only a photon can move with the speed of light.

Any massless particle must move at the speed of light. Gluons, the carrier of the strong force, are another example.

nyc1115• 2 years ago

"Any massless particle must move at the speed of light"

Does not change my argument. Human body is not a massless particle.

nyc1115• 2 years ago

I guess you guys found a way to accelerate human body to the speed of light without disintegrating. Why don't you prove your technique first with G-forces?

mftrhu• 2 years ago

accelerate human body to the speed of light

Nothing with mass can have the same speed as light, but you can trivially accelerate a human body - or something similar - to a speed which is arbitrarily close to it, without risking anything from the G-forces involved.

You just need to do it very slowly.

That is, in any case, neither here nor there, since this is a thought experiment used in a discussion about the effects of moving at a speed close to c - people in thought experiments are stronk.

itishappy4• 2 years ago

Why don't you? Here's a calculator:

https://gregsspacecalculations.blogspot.com/p/blog-page.html

1G of acceleration (which I'd hope you agree is survivable by humans) over an extended time period can easily reach relativistic speeds.

    1 day   .0028c
    1 week  .02c
    1 month .086c
    1 year  .77c
    2 years .97c
    3 years .996c
    4 years .9995c
    5 years .9999c

The thing stopping us from doing this today is economics, not physics. Current rockets have about enough fuel for minutes of acceleration, and fuel requirements increase exponentially due to the tyranny of the rocket equation. If you skip the need for fuel (laser propulsion?) and find some way to decelerate (laser cooling propulsion???), then interstellar travel to pretty much anywhere becomes entirely reasonable within human lifespans.

https://en.wikipedia.org/wiki/File:Roundtriptimes.png

ndsipa_pomu2• 2 years ago

This is not even possible in pulp science fiction

Incorrect - anything is possible in pulp scifi.

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.

Incorrect - any massless particle will move at the same speed as 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.

Incorrect - it's perfectly feasible to accelerate particles to over 99% of the speed of light. e.g. the LHC can accelerate protons to 0.999999990 c. Also, it's not possible for massless particles including photons to move at anything other than the speed of light in a vacuum, so "close to the speed of light" is not possible unless the object has mass.

Macroscopic objects cannot move with speeds approaching light speed.

Incorrect, though humans haven't been able to accelerate macroscopic (e.g. visible to human eye) objects to more than approx 0.064c (Parker Solar Probe), it's just a question of using enough power to accelerate the relevant object. There's no reason to think that a black hole accretion disk couldn't easily accelerate a lump of matter to more than 0.99c.

mr_toad• 2 years ago

Saying "close to the speed of light" changes nothing.

https://en.wikipedia.org/wiki/Oh-My-God_particle

at_a_remove2• 2 years ago

I 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.

mkleczek2• 2 years ago

The 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...

etcd2• 2 years ago

We have the sun to provide us with low entropy energy and the atmosphere to dissipate high entropy energy, so stuff tbat happens on earth can be lowering in entropy possibly. Climate change excepted.

majoe• 2 years ago

Tools from statistical physics have long been used in sociological and economical models.

It's no wonder, because statistical physics was devised as a tool for the study of complex systems.

For the same reason I don't deem entropy to be a fundamental property of physics, but one of complex systems. As far as I remember from university, the 2nd law of thermodynamics simply arises from the fact, that there are exponentially more unordered than ordered states.

Though information itself may be a fundamental physical property. The recent interest in Quantum computers shines new light on the connection between information and Quantum Mechanics. It remains to be seen, how that point of view is compatible with relativity.

I hope, that one day someone finds out, that the "time dimension" arises in the macroscopic limit from a graph of discrete causal events.

DeathArrow• 2 years ago

From the Wikipedia page on the second law of thermodynamics:

For example, the first law allows the process of a cup falling off a table and breaking on the floor, as well as allowing the reverse process of the cup fragments coming back together and 'jumping' back onto the table, while the second law allows the former and denies the latter. The second law may be formulated by the observation that the entropy of isolated systems left to spontaneous evolution cannot decrease, as they always tend toward a state of thermodynamic equilibrium where the entropy is highest at the given internal energy.[4] An increase in the combined entropy of system and surroundings accounts for the irreversibility of natural processes, often referred to in the concept of the arrow of time.[5][6]

bawana• 2 years ago

Entropy is also defined as the number of different arrangements of particles in a system. We say that entropy is increasing in our universe. But we have also found that space is increasing. If space increases faster than particles move, entropy could even decrease

itishappy4• 2 years ago

I'm in a similar boat, but I've always felt the opposite! I've always felt the second law is kind of a shoe-in and maybe even shouldn't be a law at all.

The first and third laws, "energy is never created or destroyed" and "for every action there's an equal and opposite reaction" are always true! To my knowledge, no process is ever allowed to break either law. (With exceptions for cosmological process like the expansion of the universe that we really don't purport to understand.)

The second, "entropy can only increase" isn't! That's right, I said it. The processes it describes (a cup unshuttering, or coffee unmixing, or particles all finding their way into the same side of a box) are totally legal process, albeit statistically unlikely. If you restrict your system to few enough particles (say, n=3), random processes that decrease entropy are not only possible, but something that happens with regularity!

Now, I make no claims to be right here. I suspect that Eddington fellow probably knows what he's talking about. But, this has been a longstanding thorn in my understanding of physics, so I'd be interested if anybody has any interesting insights!

elashri• 2 years ago

With exceptions for cosmological process like the expansion of the universe that we really don't purport to understand

That's not accurate, expansion of the universe (that the standard model of cosmology describes) does not violate conservation of energy. It makes it a little different from the classical view.

In classical mechanics, energy conservation is a well-defined concept in a static or non-expanding spacetime. However, in an expanding universe, especially one described by general relativity (like ours), the energy of the universe is not necessarily conserved in the traditional sense, because the global energy of the universe is difficult to define when spacetime itself is dynamic (expanding)

So GR does not require global conversation of energy in the same way classical (here classical means strictly newtonian mechanics) mechanics does. This dynamic nature of the spacetime allows for energy to appear to "change" due to the expansion. It is more complicated when you add things like dark energy to the equation.

One interesting aspect is the phenomenon of cosmological redshift. As the universe expands, light travelling through space is redshifted. This means that ita wavelength increases and its energy decreases. This "loss" of energy from light is not violating conservation of energy. It is rather consequence of the expansion itself.

Now lets back to dark energy which is driving the accelerated expansion of the universe, the energy associated with the vacuum of space remains constant per unit volume, but as space itself expands, the total energy associated with dark energy increases. This again does not violate the laws of physics because energy conservation is more complex in general relativity than in Newtonian mechanics. And of course the local energy conservation works in a well-defined way if you take a localized region of the spacetime.

alok-g2• 2 years ago

Could you pls. point to the said book or some other resource for me to learn about this? As such, I follow what you have said, but would love to see the math too. Thanks.

woopsn• 2 years ago

Ilya Prigogine wrote a lot about this, see eg Order Out of Chaos. He won the Nobel prize in chemistry for his work on nonequilibrium thermodynamics.

Boltzmann had originally tried to prove that the second law is a mechanical (statistical) fact and several others tried as well. But Poincaré showed that those systems which, regardless of their initial state, inevitably increase entropy later on inevitably reduce it (his recurrence theorem). There are also in fact reversible processes in nature, so it can't be that mechanics alone implies the procession of time. Something more involved is going on.

Carlo Rovelli has also written a lot about the "thermal time" concept in his books.

My takeaway from them is that you can't really get time out of mechanics by itself (statistical or otherwise). In the same way that you can't get baryon asymmetry. It is intrinsically a selection principle on initial conditions.

heed• 2 years ago

Also 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• 2 years ago

Wouldn’t it just happen instantly and settle on some fixed point?

Dylan168075• 2 years ago

There'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.

dcow6• 2 years ago

Could 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.

setopt2• 2 years ago

“Instant” (i.e. infinite speed of light) also permits causality. That’s the historical Galilean model.

That is in fact the only other way to make a causal universe that satisfies a few common sense assumptions (“the laws of physics are the same in every location”, “the laws of physics are the same in every direction”, “the laws of physics are the same over time”).

“One more derivation of the Lorentz transformation” by Lévy-Leblond is a very accessible derivation of this if you’re interested in reading more. It was suggested that perhaps relativity should be taught this way in high school, instead of the historical approach of “c appears to be constant in experiments, so how do we work around that with math”.

MattPalmer108611• 2 years ago

How could an effect precede a cause if there were no speed limit to causality?

No matter how fast an effect propogates, it is always after the cause (with an infinite speed, I guess effects happen instantaneously, but not before).

Of course, this doesn't fit with a universe described by general relativity, where time can be different for different observers. But you wouldn't have a universe described by general relativity without that constraint in the first place.

alde• 2 years ago

How would you compare two infinities? E.g. speed of light inside a moving train vs speed of light outside of it.

gavmor2• 2 years ago

Here's a great video explaining how, due to relativity, FTL travel can cause grandfather paradoxes: https://youtu.be/an0M-wcHw5A?si=RYFGOmQOlaC2t0bM

Edit: in short, not all reference frames can agree on the order of events, and FTL events propogate "backwards" between some reference frames.

andsoitis6• 2 years ago

How could an effect precede a cause if there were no speed limit to causality?
No matter how fast an effect propogates, it is always after the cause (with an infinite speed, I guess effects happen instantaneously, but not before).

If everything happens instantaneously then there is no real cause and effect, and the universe would be over before it really got started.

mistermann• 2 years ago

How could an effect precede a cause

I can't think of anything purely in the physical plane, though there's this:

https://en.m.wikipedia.org/wiki/Retrocausality

But if one includes metaphysics, one example (there are others) is an individual's anticipation of another individual doing something in the future could cause them to act in the present.

This is quite the stretch on its own, but if you include this (which exists, as much as people don't like to admit it depending on the context):

https://en.m.wikipedia.org/wiki/Consensus_reality

...it is possible, in that it comes down to the question of is it true that the effect proceeded the cause, and if enough people believe something is true, it is true. And if you disagree, observe human behavior for a while and see for yourself - people will tell you it is true with absolute sincerity, and they often will act in the physical plane based upon that "truth". Wars are started over "not true" "truths", perhaps even all of them.

And if that's not enough, another route is perhaps people really can see the future. People with absolute sincerity tell me they can constantly. Perhaps they are hallucinating (they swear to me they are not), but perhaps they are not, maybe it is yet another thing that science has yet to discover, or cannot discover due to non-determinism, non-falsifiability, consensus reality (a theory cannot be(!) true unless there is consensus agreement that it is true), etc.

Please don't shoot the messenger.

m3kw9• 2 years ago

Speed of light may be dependent on other constants and it will have then unpredictable effects

Etheryte3• 2 years ago

The possibility of delays being zero does not imply that negative delays are possible.

cjfd3• 2 years ago

Actually, it does. Because of relativity events that occur at the same time in one frame of reference do not occur at the same time in another. A delay of zero between two different points implies that there is a reference frame where the delay is negative.

choeger• 2 years ago

What even is the speed of causality? Is there any way to determine that causality has made it halfway from cause to effect?

Or is this just a metaphysical way of saying that no particle can move faster than the speed of light, assuming that causality is just an abstraction of moving particles around?

hughesjj• 2 years ago

Network propagation delay ;-)

Imagine the world without a speed of causality, where everything was updated instantaneously. No CAP theorm, no Byzantine generals.

Being a programmer/information theorist would be so much easier lol

crdrost3• 2 years ago

It kind of is that (a metaphysical restatement), but it's more precisely understood as a kind of half-statement of the theory.

That is, if you assume relativity, then for anything which moves faster than speed c, there exists some reference frame where it appears to move backwards in time. (This needs to be slightly qualified because it's kind of like when you're looking in a mirror and you intuitively don't think it does what it actually does -- flip front to back -- but you mentally rotate and then think that it flips left-to-right. So to be clear, if someone on a hyperluminal rocket cracks an egg into a pan, there exists someone else whose best understanding of this situation is a rocket that is traveling "backwards" engine-first, onboard of which an egg is flying up from the pan into an eggshell. But you would mentally reorient to say that the rocket is traveling "forwards" and that "forwards" direction is backwards in time.)

Now, this doesn't directly violate causality by itself, it depends on whether you can move faster than light according to an arbitrary observer. So if Carol goes faster than light according to Alice and then turns and goes faster than light according to Bob, and Bob is moving relative to Alice, only then can Carol potentially meet up with her "past self" according to Alice & Bob. The idea is that the first time she moves, Alice says she's moving very fast, but forward in time, and Bob says she's moving backward in time. Then the second time she moves, Bob says she's moving very fast, but forward in time, and Alice says she's moving backward in time. You combine these two to find that both agree that she has objectively moved backward in time.

The way this manifests in the mathematics is that in relativity, after something happens, light kind of "announces" that it happened to the rest of the world, via an expanding bubble of photons traveling away from the event at speed c. This expanding bubble is formally known as a "light cone". There is another light cone as well: before the event happens you can understand a contracting bubble of photons traveling towards the event. And basically these partition the world into five regions: The contracting bubble is the "objective past" of the event, that bubble itself is the "null past" of the event, the spacetime between the bubbles is the "general present" of the event, the expanding bubble is the "null future" of the event, and the points inside of the bubble are the "objective future" of the event. Moving faster than light, is moving from the objective future of an event, into its general present. This is "general" because different reference frames regard these points as either before or after the event in time. You need a second trajectory to then go from the general present of the event, to its objective past.

K0balt• 2 years ago

Antimatter is often described as matter going the opposite direction in time, and this seems to hold for particle interactions and quantum physics. It breaks down for thermodynamics… but might this be because of the inherent time vector of the observer?

pyinstallwoes• 2 years ago

The ontological dissonance in that title is spectacularly simulacrum level 4.

stogot• 2 years ago

I see a variety of discussions of time with different views. Is there a good summary or journal review article?

mellosouls• 2 years ago

This 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://iep.utm.edu/time/

tightbookkeeper• 2 years ago

You’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• 2 years ago

It 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.

IgorPartola2• 2 years ago

If 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.

crazydoggers2• 2 years ago

I 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.

Filligree2• 2 years ago

Photons 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.

aszantu2• 2 years ago

I 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?

Filligree2• 2 years ago

If you use seconds and light-seconds as the units instead of meters, then the magnitude of the vector is just a constant 1.

Another way of putting that: This isn’t a vector at all, it’s just a direction. Treating it as a vector gives rise to silly statements like “one second per second”, which is yet another way to explain that it’s magnitude 1… because it’s a direction.

IgorPartola2• 2 years ago

Not really because a light second is meters.

I mean like yes you can measure time and space with the same units in the way you suggest but then the concept of velocity changes as well.

itishappy4• 2 years ago

I've heard this described as "we all move at the speed of light." Also, since another way to describe alignment of two vectors is an angle, motion can be characterized by the angle it makes with the time axis.

https://www.youtube.com/watch?v=au0QJYISe4c

dbsmith83• 2 years ago

A fidget spinner illustrates this for me--bear with me. When I spin it and it just stays at rest in my hand, it spins fast. But when I quickly move my hand carrying the spinner, you can see it slows down the spin rate, and then when I stop moving it, it speeds back up. While the mechanisms are entirely different (classical vs. relativistic) they both show motion can affect certain fundamental properties of a system, whether it be spin rate or the passage of time

lacy_tinpot• 2 years ago

You can't "experience" time. Experience is memory and memory is the only thing you can "experience". Whether that memory has anything to do with time as such is debatable. Personally I'd say no.

soulofmischief2• 2 years ago

You're thinking of subjective experience, conscious perception of time. OP is referring more generally to the local speed of causality in a system at rest.

crdrost3• 2 years ago

You have understood it about as well as the article did!

Now, there is a huge nuance here, which is that you are moving near the speed of light, to certain observers. This is like the whole "relativ-" prefix in "relativity", you are at rest in your rest frame, you are moving very fast in some other rest frames. The cosmic muon crashing into Earth, sees you as time-dilated! So with that nuance "we experience time at nearly the speed of light" just becomes kind of a tautology like "we experience time how we experience time."

But a better way to think about this is, you are about two meters high, you are about a meter wide, about a half-meter dorsoventrally... and about 30 000 000 m in the other direction, if we're looking at the human reaction time/blink-of-an-eye range of 0.1s (think about how 10fps video is at the cusp of being continuous and how 20Hz is where clicks stop sounding differentiated and instead start sounding like a bass note).

What this means is that if we look at you relativistically, you kind of look like a big "rope" with worldlines of other atoms coming in, braiding into your body, eventually leaving... but the strands of this rope are bundled into these cells that have worldlines over 99.9999% parallel. (Atoms within those cells move faster, but you're probably at least 99.999% parallel even if we make that statement?) And that astonishing parallelism is precisely why relativity is not very intuitively plausible to us.

ByThyGrace• 2 years ago

and about 30 000 000 m in the other direction, if we're looking at the human reaction time/blink-of-an-eye range of 0.1s

So: distance over time, but is the time dimension only measurable in distance over time? Is there a purely time unit, or does that not make sense when speaking of spacetime?

strogonoff• 2 years ago

One of the big a-ha! moments for me was when I realized it’s possible to try (of course, impossible truly) to visualize things and people as smeared over the fourth dimension. In my case it was from trying to pinpoint what is good design, which is done in four dimensions, even if not consciously.

scotty793• 2 years ago

It's better to think that our 4 velocity always has a magnitude of 1 and use c only as a scaling factor necessary because our weird choice to use different units for time and space.

Acceleration is a rotation in this weird 3+it dimensions.

I think it better to think about 4 velocity as a unitless quantity. Because our intuitions about units and dimensions are formed by 3 dimensional space where every dimension can be swapped with any other and everything is still the same. 1 meter rotated is still 1 meter. Doesn't become 0.56m/s

pelorat• 2 years ago

Correct, it's a mathematical dimension.

quantadev3• 2 years ago

One 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).

threatripper• 2 years ago

Has this been investigated in detail by physicists? Does it hold up in theory?

quantadev3• 2 years ago

I 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• 2 years ago

I agree. The similarity between black holes and our universe is striking. The fact that matter inside it can not be observed from outside opens possibilities for all kind of quantum states, which is maybe, just the configuration of a universe (for example that one we are living in).

quantadev3• 2 years ago

There are many different "lines of reasoning" that lead to this conclusion as well. For example as an object approaches the speed of light, an observer will see it become smashed perfectly flat (length contraction) in the direction of it's travel, which is the logical equivalent of a "loss of one dimension".

In other words as something tries to "escape" our 3D manifold the effect that has is to remove one a spatial dimension. Also as something goes to nearer to speed of light, we know it also loses "time" dimension. No flow of time (from perspective of observer).

And all of these same "divide by zero" kind of impossibilities are precisely what's also happening on event horizons. In other words Special Relativity reinforces this theory. My claim is that even the Lorentz equations are showing us the way in which a dimension is lost. Lorentz is a "smooth" way of going from N dimensions to N minus 1 dimensions.

EDIT: So there must be a stronger relationship between Spinors and Lorentz than what's currently known! By having complex components, Spinors is the way to have "partial moves" in a direction, while still technically maintaining orthogonality to all other directions.

defanor• 2 years 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• 2 years ago

i'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_w2• 2 years ago

If 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.

nkrisc• 2 years ago

Think 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• 2 years ago

We 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.

glossybrown• 2 years ago

Here’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• 2 years ago

This is a well known 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• 2 years ago

Of 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.

scotty793• 2 years ago

How 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.

lottin2• 2 years ago

The refresh rate doesn't slow down, but the speed at which things change does, at high speeds.

neurotypicalc• 2 years ago

I 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

lottin2• 2 years ago

Space has no 'fabric'. Space is not a physical entity, but a set of coordinates.

Etherlord873• 2 years ago

"refresh rate" implies discrete steps, whereas not only we haven't discovered such (planck time is not it), but also we have no idea how a transition between different refresh rate would look like...

dr_dshiv• 2 years ago

To me, dimensions are just more columns in a table. Seeing in 10 dimensions? No prob.

pessimizer• 2 years ago

time is not a dimension, it's the 'refresh rate' of matter.

Exactly. Time is just a very useful fudge to describe change. If nothing changes, there's been no time. If something changes, there has been time.

A dimension is just a useful number that you can operate on. You can have a physics where the fourth dimension is how blue something is, and the fifth dimension is how good Mary thinks it tastes.

falcor84• 2 years ago

"Time is an illusion. Lunchtime doubly so."

hoseja• 2 years ago

As 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

Time is a dimension, but not like space

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