Why do we perceive a 4-dimensional universe as 3?

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Why do we perceive a 4-dimensional universe as 3?

Postby King Author » Mon Oct 14, 2013 10:28 pm UTC

I hear tell that a lotta high-level theoretical physicists believe that the universe is a single 4-dimensional object. Like, just this entity that sort of exists. The past, the future, it's all there right now. It's probably true, but begs the question -- if the universe is a 4-dimensional object, why do we experience it moment-by-moment?

If I'm a sentient fragment of this 4-dimensional object, why don't I perceive myself as such? Why do I perceive myself as a 3-dimensional being, one instant at a time?

(Kind of a big question, I know, but do we have any hunches, at least?)
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Re: Why do we perceive a 4-dimensional universe as 3?

Postby Frenetic Pony » Mon Oct 14, 2013 10:34 pm UTC

The "fourth" dimension is time, or rather a "timelike dimension" depending on what terminology you want to use. And you perceive time well enough right? Well unless you're that guy from Memento.

Why it's called a dimension goes into Relativity and time dilation. The faster you move in the first three dimensions relative to something else, the slower "through time" you are going compared to that other thing. I.E. your clocks are going slower when compared to that other things clocks. At least, that's the best explanation I can gin up, if someone can explain it better please do so.

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Re: Why do we perceive a 4-dimensional universe as 3?

Postby King Author » Mon Oct 14, 2013 10:45 pm UTC

The way I understood it was that the universe being 4-dimensional meant that the future was deterministic -- it already exists, it is what it is. The future is set and real, and the past is real as well. So if the past and future exist right now, and are real, why don't I perceive them? Why do I have to perceive the universe moment-by-moment, instead of perceiving my entire timeline at once, like Dr. Manhattan?
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Re: Why do we perceive a 4-dimensional universe as 3?

Postby Frenetic Pony » Mon Oct 14, 2013 10:53 pm UTC

King Author wrote:The way I understood it was that the universe being 4-dimensional meant that the future was deterministic -- it already exists, it is what it is. The future is set and real, and the past is real as well. So if the past and future exist right now, and are real, why don't I perceive them? Why do I have to perceive the universe moment-by-moment, instead of perceiving my entire timeline at once, like Dr. Manhattan?


You can get one of two answers
A: It's described as a timelike dimension because it appears you can move faster or slower in that dimension compared to other things and the math (at least with relativity) works out something like you would work out other "dimensions" with so calling it a dimension is convenient.

B: If "A" is somehow unsatisfactory then you get into questions about fundamental physics and eventually crossover with fundamental mathematics and hypothesis so convoluted they take entire books to explain with titles like "The arrow of time" or etc. A lot of the discussion of which may or may not have anything to do with "what time is" at all depending on who you ask. I.E. it's a complicated and very fun subject if you are really interested.

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Re: Why do we perceive a 4-dimensional universe as 3?

Postby King Author » Mon Oct 14, 2013 10:58 pm UTC

Huh. Now that you mention it, I do remember a part of A Brief History of Time touching on why we perceive time as moving forward, rather than backward, and the Arrow of Time thing, but it didn't really go into why we perceive time as moments rather than all at once.
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Re: Why do we perceive a 4-dimensional universe as 3?

Postby tooyoo » Mon Oct 14, 2013 11:52 pm UTC

King Author wrote:Why do I have to perceive the universe moment-by-moment, instead of perceiving my entire timeline at once, like Dr. Manhattan?


Actually, neither is correct. Strictly speaking you're not perceiving the universe moment by moment, nor in its entirety.

Think about it. Let's say you're sitting in a room, about a meter away from a candle. Seeing the candle, you see the light it emitted about 3 nanoseconds ago (1m divided by the speed of light). If there's a second candle two meters away, you perceive at the same time the first candle, still 3 nanoseconds ago, and the other one, now 6 nanoseconds ago (2m divided...). So you see, the only thing you perceive in its entirety at any given moment is you (i.e. the place where you are). Otherwise you're always perceiving the past.

The technical expression is to say that you always perceive what's in your past light cone - i.e. that region of space that can transmit light signals to you.

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Re: Why do we perceive a 4-dimensional universe as 3?

Postby elasto » Tue Oct 15, 2013 12:20 am UTC

In our universe, causes always precede effects: a cause is always in the past of an effect. And, yes, this is deeply intertwined with entropy (aka the arrow of time).

Think about what it means to experience something: It means that something in the universe caused a change in your mental state: Might be a photon hitting your retina causing an electrical impulse to change the state of a neuron or whatever.

So this is why we remember the past and not the future - because only past events can cause changes in our mental state.

The reason why our 'conscious experience' - ie. what we call 'the present' - is so short is probably down to processing power: It's just more efficient to only be conscious of the present - and experience the past as memories - ie. as filtered and compressed data*. But it seems to me there's no reason in principle why 'now' couldn't stretch from the tenth of a second or so it currently lasts to minutes, hours or even the whole of our past life.

As to why we are conscious at all rather than unthinking machines - well, that's a much deeper question.

[*Actually, even what we experience as 'the present' is a highly, highly compressed and filtered version of the real-time data coming in from our senses. But what we experience as 'the past' - ie. our memories - is even more filtered and compressed. We do compression and filtering algorithms that Google could only dream of.]

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Re: Why do we perceive a 4-dimensional universe as 3?

Postby Meteoric » Tue Oct 15, 2013 2:46 am UTC

I don't know nearly enough to provide a decent and technically-accurate explanation, but it is my understanding that the time dimension is distinctly different than the three spatial dimensions: "3+1-D" is different than "4-D". Orthogonal is a novel exploring what a 4-D universe might look like.
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Re: Why do we perceive a 4-dimensional universe as 3?

Postby King Author » Tue Oct 15, 2013 1:24 pm UTC

tooyoo wrote:
King Author wrote:Why do I have to perceive the universe moment-by-moment, instead of perceiving my entire timeline at once, like Dr. Manhattan?


Actually, neither is correct. Strictly speaking you're not perceiving the universe moment by moment, nor in its entirety.

Think about it. Let's say you're sitting in a room, about a meter away from a candle. Seeing the candle, you see the light it emitted about 3 nanoseconds ago (1m divided by the speed of light). If there's a second candle two meters away, you perceive at the same time the first candle, still 3 nanoseconds ago, and the other one, now 6 nanoseconds ago (2m divided...). So you see, the only thing you perceive in its entirety at any given moment is you (i.e. the place where you are). Otherwise you're always perceiving the past.

The technical expression is to say that you always perceive what's in your past light cone - i.e. that region of space that can transmit light signals to you.

At the risk of sounding jerky, yeah, I know that already. Whether I'm perceiving my past light cone or whatever, though, the fact remains I only perceive one moment at a time, rather than perceiving my entire four-dimensional self. I'm wondering -- why should that be?

elasto wrote:In our universe, causes always precede effects: a cause is always in the past of an effect. And, yes, this is deeply intertwined with entropy (aka the arrow of time).

Think about what it means to experience something: It means that something in the universe caused a change in your mental state: Might be a photon hitting your retina causing an electrical impulse to change the state of a neuron or whatever.

So this is why we remember the past and not the future - because only past events can cause changes in our mental state.

The reason why our 'conscious experience' - ie. what we call 'the present' - is so short is probably down to processing power: It's just more efficient to only be conscious of the present - and experience the past as memories - ie. as filtered and compressed data*. But it seems to me there's no reason in principle why 'now' couldn't stretch from the tenth of a second or so it currently lasts to minutes, hours or even the whole of our past life.

As to why we are conscious at all rather than unthinking machines - well, that's a much deeper question.

[*Actually, even what we experience as 'the present' is a highly, highly compressed and filtered version of the real-time data coming in from our senses. But what we experience as 'the past' - ie. our memories - is even more filtered and compressed. We do compression and filtering algorithms that Google could only dream of.]

What I'm trying to wrap my head around is -- if the universe is deterministic (which physicists seem to think, and they're probably right), if the future already exists and is real, why am I only perceiving a fraction of it? If the universe is a single 4-dimensional object, just this thing floating in space, if you will, and if I have perception, which let's just skip the metaphilosophy and assume I do, why don't I perceive myself as the 4-dimensional smear in the universe that I am?

Meteoric wrote:I don't know nearly enough to provide a decent and technically-accurate explanation, but it is my understanding that the time dimension is distinctly different than the three spatial dimensions: "3+1-D" is different than "4-D". Orthogonal is a novel exploring what a 4-D universe might look like.

I'm not having trouble picturing a 4-dimensional universe, I'm wondering why my perception isn't continuous across my past, present and future. I can't see any reason why I should be "stuck in the present," if the future already exists, and is real, and I'm already "there."
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Re: Why do we perceive a 4-dimensional universe as 3?

Postby eSOANEM » Tue Oct 15, 2013 2:45 pm UTC

When scientists say the universe is deterministic they no longer mean that in the naive sense of "physical observables evolve deterministically". Bell's theorem knocked that idea on the head and instead we have this concept where we have some quantity which is only indirectly observable which does evolve deterministically (assuming you're not observing anything) and that all of this closely approximates a deterministic universe at large scale.

Ignoring QM for now though and pretending that relativity is the weirdest the universe gets and therefore it is meaningful to talk about determinism naively, we can still see that seeing your whole timeline at once is impossible.

Thought is a process, and so it must take some time to have a thought. Obviously consciousness requires thought so a conscious entity must exist and be conscious over some interval of time rather that a discrete moment. Now, let us consider a conscious entity which can observe the entirety of its wordline at once. Because of lightspeed propagation and causal connection, this means the entirety of the entity's worldline must be in its past light cone (the non-relativistic form of this point is trivial). There is only one point on an entity's worldline where its whole wordline is in its past light cone and this the end of the entity's worldline.

We did, however, previously require that a conscious entity exist over an interval on a worldline rather than a single point hence we have a contradiction and thus demonstrate that even naive determinism is capable (together with causality) to prove the idea of perceiving your whole timeline impossible.

I'm pretty sure however that the type of perception of your whole timeline is one unlike that I constructed and instead is like dr manhattan's where you are sentient over your entire life but know everything that will ever happen to you. Essentially a power where you can remember your future as well as your past. The only way for such a power to exist is if we drop causality (but leave our determinism naive; a proper QM-consistent notion of determinism would make this sort of thing impossible on its own) and essentially send all the information back in time.

This is why people keep talking about the arrow of time.

It is the important factor here.

It is what makes this impossible.
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Re: Why do we perceive a 4-dimensional universe as 3?

Postby elasto » Tue Oct 15, 2013 3:22 pm UTC

King Author wrote:What I'm trying to wrap my head around is -- if the universe is deterministic (which physicists seem to think, and they're probably right), if the future already exists and is real, why am I only perceiving a fraction of it? If the universe is a single 4-dimensional object, just this thing floating in space, if you will, and if I have perception, which let's just skip the metaphilosophy and assume I do, why don't I perceive myself as the 4-dimensional smear in the universe that I am?

I addressed that in the first part:

me wrote:Think about what it means to experience something: It means that something in the universe caused a change in your mental state: Might be a photon hitting your retina causing an electrical impulse to change the state of a neuron or whatever.

So this is why we remember the past and not the future - because only past events can cause changes in our mental state.


Consciousness isn't 'magic', it's just another physical process governed by the normal laws of cause and effect. We can't be conscious of future events; only past events can be a cause that changes our mental state.

In another universe where cause and effect could work backwards as well as forwards, our perception of 'now' would stretch both forwards and backwards in time. With a large amount of processing power, we could be conscious of our entire existence as a 4d smear as you suggest.

Coming back to our universe though, even if the future is determined (which is actually too complicated a topic to give a simple yes/no answer to) - at whatever point in time we're talking about, the future cannot effect a physical change in our brain as of at that time, so we can't be conscious of anything in our future. This is true even if time doesn't really move at '1sec/sec forwards' as we perceive it to but 'jumps around at random' or even 'runs backwards'... We'd perceive it to run at 1sec/sec forwards no matter how it 'really' changed - for exactly the same reason: We can only remember the past not the future, and 1 second ago and 2 seconds ago are different to us because we remember that, 1 second ago, 2 seconds ago was only 1 second ago... So we perceive a flow - whether or not it 'actually' occurs.

Being able to perfectly predict the future, were that possible in some perfect physics GUT, is still not the same as consciously experiencing the future.
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Re: Why do we perceive a 4-dimensional universe as 3?

Postby Tchebu » Tue Oct 15, 2013 3:44 pm UTC

Your mental state evolves as you follow your brain's worldline (I guess worldvolume, really) due to interactions with the rest of the universe. What we typically call "you" is a cross-section of that worlvolume at fixed time (or over some limited time interval at least). So your sequencial perception of the universe is a direct consequence of the implicit definition of "you" that we all use.
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Re: Why do we perceive a 4-dimensional universe as 3?

Postby lgw » Tue Oct 15, 2013 5:23 pm UTC

Well, obviously we perceive one dimension as "time". It is mathematically different from the space dimensions, of course, thus the (+ + + -) signature, or however that goes - time is imaginary. Nevertheless our perception in the time dimension leaves something to be desired: "it's a poor sort of memory that only works backwards"!
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Re: Why do we perceive a 4-dimensional universe as 3?

Postby Meteoric » Tue Oct 15, 2013 5:43 pm UTC

King Author wrote:why don't I perceive myself as the 4-dimensional smear in the universe that I am?

Well, you do. You perceive time passing, yes?

You don't perceive it all simultaneously for reasons similar to why you don't occupy every point in space simultaneously. Any given instance of "you perceive" is a single event in spacetime; the configuration that we refer to as "you" is a collection of such events.

I'm super unsure that timeful words like "already" can be non-misleadingly used to describe the universe from an outside-of-time perspective.
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Re: Why do we perceive a 4-dimensional universe as 3?

Postby stianhat » Wed Oct 16, 2013 7:48 am UTC

Well, seeing as you only have freedom to navigate only 3 dimensions - the fourth one is inherently plodding along its linear (supposedly) track. Had you been able to go forward or backward in time as easily as you change your spatial orientation and position, well - the universe would have appeared 4-dimensional (but you would need a "temporal sense" that you could percieve the 4-D-ness with or else it would not be coherent at all.)

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Re: Why do we perceive a 4-dimensional universe as 3?

Postby WibblyWobbly » Wed Oct 16, 2013 4:05 pm UTC

stianhat wrote:Well, seeing as you only have freedom to navigate only 3 dimensions - the fourth one is inherently plodding along its linear (supposedly) track. Had you been able to go forward or backward in time as easily as you change your spatial orientation and position, well - the universe would have appeared 4-dimensional (but you would need a "temporal sense" that you could percieve the 4-D-ness with or else it would not be coherent at all.)

I used to be able to do that, but ever since the fall of Gallifrey, it's just not the same.

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Re: Why do we perceive a 4-dimensional universe as 3?

Postby dudiobugtron » Wed Oct 16, 2013 7:57 pm UTC

Here's a slightly different way to think about some of the stuff that other posters have already said:

An outside observer somehow looking in at our 3+1 universe would see me perceiving each moment in time I perceived. At any moment in time, they could look and see me perceiving at that time. From their point of view, I am perceiving it 'all at once', or, at least, all the instances of me are perceiving it collectively 'all at once'.

However, from the point of view of any of the 'me' instances, all I am perceiving is that moment in time. Because of the way I am made up, I interpret a lot of this perception as memories of the past. There is nothing special about a particular instance of me, and there isn't a 'me' instance that is 'now', as opposed to the past and future mes. All of them are 'now' according to their perception.

So, basically, for any moment in time you exist in, there is a version of you perceiving it. You aren't travelling through time at all, it just seems like that to each of your individual 'instances'. The you that thinks it is reading this post isn't a priveledged version of you, it's just one of the many other yous who also thinks they are the priveleged version of you. Of course, it isn't even really reading, or thinking, or doing anything else that requires the passage of time. It just appears that way to it.
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Re: Why do we perceive a 4-dimensional universe as 3?

Postby doogly » Wed Oct 16, 2013 8:14 pm UTC

And it's nice to bring quantum mechanics in. We are generally ready to wipe the sweat off our brow, quantum mechanics restores some randomness and indeterminacy to the future! Yay! This jives with what most people like. A deterministic future is a bit of a buzzkill.

But the past too is in trouble now. There is not one unique past history which is anointed as "real." If you have a set of observables, and you want to know what the past was, what could have sent you those signals, you have to do the sum over paths a la Feynman in exactly the same way as if you were trying to predict some future or some transmission probability. There's no difference. And again, it would be quite problematic to call the future uncertainy ontological and the past uncertainty purely epistemic - it's ontologies all around.

So that's exciting.
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Re: Why do we perceive a 4-dimensional universe as 3?

Postby eSOANEM » Thu Oct 17, 2013 5:36 pm UTC

doogly wrote:But the past too is in trouble now. There is not one unique past history which is anointed as "real." If you have a set of observables, and you want to know what the past was, what could have sent you those signals, you have to do the sum over paths a la Feynman in exactly the same way as if you were trying to predict some future or some transmission probability. There's no difference. And again, it would be quite problematic to call the future uncertainy ontological and the past uncertainty purely epistemic - it's ontologies all around.


Isn't this true classically (albeit only at a macroscopic scale) and isn't this the argument behind last thursday-ism?
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Re: Why do we perceive a 4-dimensional universe as 3?

Postby doogly » Thu Oct 17, 2013 5:42 pm UTC

Classically everything is deterministic and there is only epistemic uncertainty, regarding things like chaos or thermodynamics or what have you.
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Re: Why do we perceive a 4-dimensional universe as 3?

Postby thoughtfully » Thu Oct 17, 2013 7:46 pm UTC

But if sufficient knowledge is unattainable in practice, does it still have epistemic status?

Or indeed, if it takes forever to read the dial of an infinitely precise instrument..
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Re: Why do we perceive a 4-dimensional universe as 3?

Postby gmalivuk » Thu Oct 17, 2013 7:53 pm UTC

That's still epistemic, because you're still positing that the instrument has infinite precision even if it takes forever to know it.
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Re: Why do we perceive a 4-dimensional universe as 3?

Postby lgw » Thu Oct 17, 2013 8:14 pm UTC

dudiobugtron wrote:Here's a slightly different way to think about some of the stuff that other posters have already said:

An outside observer somehow looking in at our 3+1 universe would see me perceiving each moment in time I perceived. At any moment in time, they could look and see me perceiving at that time. From their point of view, I am perceiving it 'all at once', or, at least, all the instances of me are perceiving it collectively 'all at once'.

However, from the point of view of any of the 'me' instances, all I am perceiving is that moment in time. Because of the way I am made up, I interpret a lot of this perception as memories of the past. There is nothing special about a particular instance of me, and there isn't a 'me' instance that is 'now', as opposed to the past and future mes. All of them are 'now' according to their perception.

So, basically, for any moment in time you exist in, there is a version of you perceiving it. You aren't travelling through time at all, it just seems like that to each of your individual 'instances'. The you that thinks it is reading this post isn't a priveledged version of you, it's just one of the many other yous who also thinks they are the priveleged version of you. Of course, it isn't even really reading, or thinking, or doing anything else that requires the passage of time. It just appears that way to it.


The word "eternal" precisely describes that "outside observer somehow looking in at our 3+1 universe" - strictly speaking, eternal means "outside of time", not "forever". Western theologians (which included pretty much all the geeks pre-Enlightenment) have spent 1000 years arguing about the ramification of that. What opinion do you have on free will if we postulate the existence of an eternal observer? For any opinion you might have, there will be hundreds of well written arguments defending that position, and thousands attacking it. You do have to shift your technical terminology to make sense of it all, of course, but it's amazing how much mental effort has gone into topics like this (and how sadly little of it has made onto the internet, especially in translation).
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Re: Why do we perceive a 4-dimensional universe as 3?

Postby eSOANEM » Thu Oct 17, 2013 10:47 pm UTC

True. I was thinking that, generally, it is not feasible to get the momentum and position of every particle in a classical body and so we only get indirect statistical measures like temperature and entropy. Of course there is nothing fundamental which prevents you from finding out such information (in a classical setting) so I suppose I ought to have said in classical statistical mechanics instead. *shrug*
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Re: Why do we perceive a 4-dimensional universe as 3?

Postby lgw » Fri Oct 18, 2013 12:04 am UTC

I don't think anything rules out a deterministic underpinning for quantum mechanics, if the deterministic part is far down the scale ladder (of course, you must explain spooky action at a distance, somehow). The probabilistic model in QM makes really good predictions, of course, but it's easy to imagine (qualitatively!) e.g. the electron being a collection of entities at Plank scale with the observed collective probabilistic behavior (and the same inability to measure both elements of an uncertainty-pair).

Of course, just saying so qualitatively isn't science - but questions of determinism are as much philosophy.
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Re: Why do we perceive a 4-dimensional universe as 3?

Postby gmalivuk » Fri Oct 18, 2013 12:06 am UTC

Except, you quickly run afoul of Bell if you're not very careful with how your determinism works.
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Re: Why do we perceive a 4-dimensional universe as 3?

Postby doogly » Fri Oct 18, 2013 3:35 am UTC

Most of the time people only ever want determinism to mean "determined by local causes," and that is the thing that is right out.
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Re: Why do we perceive a 4-dimensional universe as 3?

Postby lgw » Fri Oct 18, 2013 5:47 pm UTC

doogly wrote:Most of the time people only ever want determinism to mean "determined by local causes," and that is the thing that is right out.


Quite well put! What you can't get is underpinnings that are classical, but it's really locality that's broken, not deterministic behavior. I believe that's the lesson from particle/wave duality, really. IMO what we think of as "fundamental entities" in the current model are really quite large - at least "wavelength-sized" if not much larger - but for any single measurement it just looks like any two such entities have interacted at some specific point.

I think it's a good qualitative mental model to think of e.g. electrons and photons as clouds of many smaller "virtual" mini-particles, that interact when any one virtual particle from each "collide" (interact at some much smaller scale): you can thus think of the probabilistic location of e.g. an electron as the distribution of this cloud. (Though I wonder if "virtual particle" hasn't taken on too much meaning these days and maybe I need a new word.) No difference in the math, but it's easier to understand and teach IMO as it's closer to intuition. While you can expand this to explain entanglement in terms of spooky action at a distance with this mental model (entanglement being exchange of virtual mini-particles), that doesn't really help make it any more intuitive unless you add an FTL element between these virtual mini-particles, which probably goes a bit far.
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Re: Why do we perceive a 4-dimensional universe as 3?

Postby doogly » Fri Oct 18, 2013 6:06 pm UTC

"virtual particle" is a step backwards. Eschew particles, embrace fields.
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Re: Why do we perceive a 4-dimensional universe as 3?

Postby lgw » Fri Oct 18, 2013 7:47 pm UTC

doogly wrote:"virtual particle" is a step backwards. Eschew particles, embrace fields.


Yeah, perhaps I need a new word, I certainly didn't mean "virtual photons" in the sense one might model the "electric field" around an electron. But if you're talking about e.g., the "electron field", the idea that electrons aren't discrete entities, there's just this universal "field" that describes the probability that there's an electron at any given place, that's precisely what I'm trying to get away from. That's about as non-intuitive as it gets - nonsense with none of the charm of Lewis Carroll.
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Re: Why do we perceive a 4-dimensional universe as 3?

Postby Tchebu » Fri Oct 18, 2013 8:06 pm UTC

What's wrong with fields? You have no trouble accepting classical electromagnetism I presume? And then it turned out there was a particle-like aspect to its excitations. Why do electrons have to be tiny balls of stuff instead of packets of excitations?
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Re: Why do we perceive a 4-dimensional universe as 3?

Postby doogly » Fri Oct 18, 2013 8:14 pm UTC

Word. If fields are not intuitive, cultivate your intuition until they are.
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Re: Why do we perceive a 4-dimensional universe as 3?

Postby lgw » Fri Oct 18, 2013 9:43 pm UTC

Tchebu wrote:What's wrong with fields? You have no trouble accepting classical electromagnetism I presume? And then it turned out there was a particle-like aspect to its excitations. Why do electrons have to be tiny balls of stuff instead of packets of excitations?


doogly wrote:Word. If fields are not intuitive, cultivate your intuition until they are.


"If it's hard to teach, the problem lies with the student" - most professors I've met.

It's not that fields per se are non-intuitive. Force fields, like the electric field, are the most intuitive presentation. It matches how we naively think of action at a distance.

But field representations of matter? Quite the opposite. Matter is obviously tiny balls of stuff, says naive intuition. Any other mental model requires considerable training just to catch up. Why do that if you could have a model that's both intuitive and accurate?
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Re: Why do we perceive a 4-dimensional universe as 3?

Postby ahammel » Fri Oct 18, 2013 11:56 pm UTC

lgw wrote:Matter is obviously tiny balls of stuff, says naive intuition.
So you just look at, say, cheese and you intuition goes "oh yeah, that's obviously made of quarks", does it?
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Re: Why do we perceive a 4-dimensional universe as 3?

Postby doogly » Fri Oct 18, 2013 11:58 pm UTC

But it is wrong. There is no difference between the electric field and the electron field. It's all fields.

Like, what precisely are you proposing? A particle based alternative to QFT that is just as accurate?
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Re: Why do we perceive a 4-dimensional universe as 3?

Postby thoughtfully » Sat Oct 19, 2013 1:26 am UTC

ahammel wrote:
lgw wrote:Matter is obviously tiny balls of stuff, says naive intuition.
So you just look at, say, cheese and you intuition goes "oh yeah, that's obviously made of quarks", does it?

Perhaps not, but I know some quarks that are made of cheese!
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Re: Why do we perceive a 4-dimensional universe as 3?

Postby Tchebu » Sat Oct 19, 2013 3:31 am UTC

Matter is obviously tiny balls of stuff, says naive intuition.


Well, no... It's just that we're used to hearing about atoms from a young age nowadays. Upon first inspection matter actually looks like a continuous lump that somehow stays in one piece and that's about as much as you can say about it.

Moreover, as soon as you know anything at all about waves it becomes pretty obvious that things that look like cohesive lumps that move as one don't necessarily have to consist of smaller pieces moving together, so it really doesn't take much to blow any intuition about it being made of tiny balls out of the water.
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Re: Why do we perceive a 4-dimensional universe as 3?

Postby PM 2Ring » Sat Oct 19, 2013 4:46 am UTC

lgw wrote:
doogly wrote:"virtual particle" is a step backwards. Eschew particles, embrace fields.


Yeah, perhaps I need a new word, I certainly didn't mean "virtual photons" in the sense one might model the "electric field" around an electron. But if you're talking about e.g., the "electron field", the idea that electrons aren't discrete entities, there's just this universal "field" that describes the probability that there's an electron at any given place, that's precisely what I'm trying to get away from. That's about as non-intuitive as it gets - nonsense with none of the charm of Lewis Carroll.


I think the word you're looking for is quasiparticle.

Why are you trying to get away from "there's just this universal "field" that describes the probability that there's an electron at any given place"?

Personally, I like the cellular automaton approach: an electron is like a glider in Conway's Game of Life. It appears to be an oscillating entity that moves in a certain way, but really it's just an evolving pattern of the underlying substrate (the electron field).

doogly wrote:But it is wrong. There is no difference between the electric field and the electron field. It's all fields.

To be fair, there is a major difference. But it's not that the electromagnetic field is more wave-like and the electron field is more particle-like, which is where I believe a lot of people get misled. The major difference (as you well know) is that of the symmetry properties, i.e Bose-Einstein v Fermi-Dirac.

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Re: Why do we perceive a 4-dimensional universe as 3?

Postby doogly » Sat Oct 19, 2013 5:21 am UTC

I just meant that there is no difference in their field-ness. Mass also stands out as rather different.
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Re: Why do we perceive a 4-dimensional universe as 3?

Postby PM 2Ring » Sat Oct 19, 2013 8:14 am UTC

doogly wrote:I just meant that there is no difference in their field-ness.

Fair enough.

doogly wrote:Mass also stands out as rather different.

Quite!

OTOH, if we want to be pedantic, wouldn't it be more accurate to say that an electron's mass is not intrinsic to the electron field itself but is instead due to (indirect) coupling with the Higgs field(s)?


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