the speed of light question

Speed of light is constant. We observe passage of time because things happen at different times.

This is exactly the statement that i'm looking to answer. You're not explaining it, just making a statement. Why do things happen at different times?

I'll try to explain my thinking again. Cut an elastic band and then hold the two ends together. You then pull one end away from the other at a theoretical speed of light. At the speed of light end there is no time (we know this), and at the stationary end there is no speed at all therefore there is no light/energy/time at all, just nothing.

It is what's happening along the elastic expanding at various speeds between the two that gives rise to time. Each section takes a longer time to reach the point that the previous section passed, before they themselves eventually run out of energy and stop becoming dark.

This is the universe to my mind. Everyone can wax lyrical about what they've been taught to be the accepted knowledge but as far as i know no one has discovered why we age. I'm happy with my own answer.

Nexytus wrote: »

Does it need to be an elastic band? Or could it be a string?

Laugh away.
My theory is a plausible explanation as to why we are alone in the entire universe. Every other possible life-form exists at a different speed of light to ours, therefore connectivity between the two is not possible, or is it? Time will tell.
As we already know there are particles which are visible at the speed of our light.
Is it these particles which transfer our genes from one generation to the next?

Eventually is it possible that beings will develop entirely made up of these time resistant particles who could theoretically make contact.

Laugh again if you wish. At least i am trying to find an answer.

Nexytus wrote: »

Maybe not different speeds of light but different particles and waves that do not interact with any of the particles that we are aware of and that make up our physical world. So there could be other worlds layered over ours but which we can never know of or interact with.

The only existing phenomenon that we are aware of is the affect of the speed of light on our perception of time. I don't know why we are striving to explain things that we don't understand on some other unknown concept.

I am simply expanding on what we already know to be true and positing theories based on that.

Nexytus wrote: »

Does it need to be an elastic band? Or could it be a string?

standardg60 wrote: »

Laugh away.

Nexytus’ comment was actually quite smart, given the topic. Although you’d have to be aware of String Theory to get it.

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

y0ssar1an22 wrote: »

i think the end result is that we think we know, but we don't really know. otherwise, why change rules at a certain speed?

But we don't change the rules at a certain speed. The equations work equally well for any speed. It's just that there's a hard limit, and for very good reasons. To break that hard limit would require more than infinite energy, which can't exist. There's very sound theoretical, mathematical and practical reasons for it being both a constant and a limit.

You can't say "we don't really know" if you don't actually know what we actually do know in the first place.

Physics isn't like philosophy. In philosophy, you can come up with an idea and argue for it. Or against it. Whether it stands or not is based on some external assumptions and how internally consistent it is. In physics, when you come up with an idea, it actually has to work. It has to explain something about what we see and experience, and it has to be experimentally verifiable. Otherwise it's utterly pointless.

Both Newton's theory of gravity and Einstein's general theory of relativity predict that light will bend around a massive object, a phenomenon known as gravitational lensing. Neither of them witnessed or experienced this, it was merely something that their equations say should happen. It wasn't until 1919 that it was first experimentally observed in real life. It's now used by astronomers in observing the distant universe. If it had been shown not to occur, then both Newton's theory of gravity and Einstein's general theory of relativity would have been shown to be fundamentally flawed, and they would have been relegated to the scrapheap of theories, like Aristotelian physics, the Copernican system the Steady State theory. But they weren't. This is just one of the many examples of experimental evidence upholding the theories. All it takes is one verified falsification to unseat a theory. (in fact, Newton's theory of gravity has been proven to to be wrong, but because it works well at approximate values at speed that aren't close to the speed of light, it's still useful in day-to-day calculations and explanations).

That's not to say that all questions have been answered, or that the theories are perfect. They're not, and there are gaps, and people are constantly working on new theories to fill those. But we do know a lot, and any new theory that's going to replace and improve upon what we have now has to take into account what we already know and observe. Relativity and the various theories of quantum mechanics will be superseded by something someday - but that thing that superseded them not only has to work as well as them, but has to work better.

It's not just a matter of thinking "oh, maybe it's this way, who really knows". We do know, and we know it actually has to work.

Elianna Future Turbojet wrote: »

This is fascinating. I am a complete layperson in all this but (I assume you mean neutrino) the neutrino was hypothesised initially because there was some element missing from some equation right, i.e. (I know this isn't it but a thought experiment) when you split an atom the mass of the two halves didn't add up to the mass of the original atom, so you had your original atom = two halves + energy + whatever else.

So there's no zero sum out there, that says the neutrino, even though we can't detect it, HAS to be this certain portion of the mass/energy/whatever that comes from some reaction or process, because we've accounted for everything else?

I don't know if any of that makes sense.

Sorry, yeah, that was a typo, I did mean to type neutrino.

There's a whole question of missing mass in the universe. We know from the way gravity works that what we observe happening in the motion or galaxies should not be happening given the amount of stars and gas we see in them. Either the theory is very wrong, or there's mass - a lot of mass - that we can't detect. Now, the theory can't be totally wrong because it works so well. And there's a lot of experimental and observational evidence that there is missing mass. It's an ongoing investigation, but there's various candidates for it that are theoretically possible - but they haven't been detected yet. There's experiments underway and proposed to determine if any of these candidates actually exist.

As you say, neutrinos were proposed as having to exist in 1930 to account for how beta decay in atoms works, before they were observed. There was a bit missing from the observations and calculations, and something had to fill it. Thus the neutrino was proposed (although confusingly, Pauli called it a "neutron". In 1932, Chadwick discovered a much more massive neutral nuclear particle inside atoms, and he decided to call it the "neutron". The diminutive term "neutrino" was then coined for the particle Pauli proposed, as it was expected to be much less massive (or have no mass).

It wasn't until 1956 that neutrinos were actually detected in an experiment, and 1965 that they were detected in nature. They interact with matter so little that they're exceptionally difficult to detect, but they're everywhere. It's estimated that each second, 65 billion of them pass though every square centimeter of your body surface - and that's just the ones coming from the sun - they're also coming from objects in the rest of the universe and indeed the Big Bang itself.

When it was discovered that neutrinos had some mass (albeit very, very, very little), then it was proposed that they were a candidate for some of this missing mass of the universe. It's since been shown that while they certainly do make up some of the missing mass, it's only a very small proportion. The rest of it - the vast bulk of it - is still subject to ongoing investigation.

So like the way the neutrino was proposed as having to exist before it was actually discovered, other forms of matter (mass) and energy that we don't know about yet must also exist. But, they must exist within some very clearly defined parameters, so this isn't carte blanche for people to propose all kinds of fanciful notions. There's a very specific gap that they must fill in the theories and observations,.

Mellor wrote: »

That statement, as simplistic as it seams, is all that is needed to explain your query.

You are reading this post now, and not the last time you were online because it didn't exist then. Nothing to do with a variable speed of light. If light was 10x faster or slower, it wouldn't have made a significant difference to when it got to you.


It's the part at the end if bold that is where this goes wrong. And undermines everything afterthat.
If something is stationary, that doesn't mean there is no light/energy/time. Not sure where you are getting that from. It that were the case as some as anything stopped moving it would ceases to exist.



No it isn't.


They take a longer time to reach the point because the are moving at a different speed, ie not at the speed of light. Taking longer to reach the point just means they take longer. Same way that a car driving slower takes longer to get from A to B. None of that.



We know why we age. And nothing in your theory would offer a and explanation for why we age and for time.


If another lifeform operated on a different speed of light. It wouldn't stop us seeing or interacting with them. We wouldn't even perceive a difference face to face.


No. Genes are transfer via reproductive cells not photons.

Thanks for taking the 'time' to respond to each of my points in turn. I'll respond likewise.

I know i'm only reading it now, and i know it didn't exist yesterday. What i'm asking, thinking, is why we are on this trajectory of what we perceive to be time, what is causing it?

What i mean is all light has left that point. My thinking is that nothing can exist without the movement of light because that is what creates existence. If there is no light moving there is no time, if there is no time there is no existence.

What gives rise to time then if it's not the movement of light?

Accepting that they just 'take longer' is exactly what i don't accept. If one car reaches B instantaneously, nothing has 'happened' to the occupants. Meanwhile the occupants of the slower car have aged, reproduced, died, and never arrived at all, but their descendants (genes, DNA) did.

As far as i know we don't know why we age, just how we age. Yes cells reproduce and degrade over time but what causes them to reproduce at all? What external phenomenon are they responding to?

If another life form where out there existing in a different speed of light to ours we would be invisible to each other unless one had developed the ability to exist within the other's light speed. That they were entirely made up of cells which didn't need to reproduce in response to the passing of time.

Why do we reproduce at all? For me reproduction is life's/ Existence's naturally developed defence against the passing of time. Saying it's merely the reproduction of cells ( which again is saying how it happens rather than why) does not answer the question i ask.

I'm possibly/ probably talking a load of nonsense here but i thought it was time to put my thoughts in writing!

standardg60 wrote: »

I know i'm only reading it now, and i know it didn't exist yesterday. What i'm asking, thinking, is why we are on this trajectory of what we perceive to be time, what is causing it?

It’s caused, precisely by the passage of time.

What i mean is all light has left that point. My thinking is that nothing can exist without the movement of light because that is what creates existence. If there is no light moving there is no time, if there is no time there is no existence.

Light doesn’t create existence or time.

What gives rise to time then if it's not the movement of light?

It’s simply something that happens. Regardless of light. If you entered a room in total darkness with zero light. Time would still pass.

Accepting that they just 'take longer' is exactly what i don't accept. If one car reaches B instantaneously, nothing has 'happened' to the occupants. Meanwhile the occupants of the slower car have aged, reproduced, died, and never arrived at all, but their descendants (genes, DNA) did.

If they are travelling at different speeds the cars aren’t connected. There is nothing different about your example as a car at 20km/h and another at 80km/h.

As far as i know we don't know why we age, just how we age. Yes cells reproduce and degrade over time but what causes them to reproduce at all? What external phenomenon are they responding to?

No phenomenon. External or internal required.
This is basic biology, not physics btw.

If another life form where out there existing in a different speed of light to ours we would be invisible to each other unless one had developed the ability to exist within the other's light speed.

No we wouldn’t.
If you emitted lighted light twice as slow, I would see you just fine.
You seem to misunderstand what “the speed of light” actually means.

That they were entirely made up of cells which didn't need to reproduce in response to the passing of time.

Why do we reproduce at all? For me reproduction is life's/ Existence's naturally developed defence against the passing of time. Saying it's merely the reproduction of cells ( which again is saying how it happens rather than why) does not answer the question i ask.

Reproduction doesn’t defend time. No more than condone allow you to time travel.

standardg60 wrote: »

What gives rise to time then if it's not the movement of light?

Time was created in the Big Bang, along with space. It’s an inherent property of the universe. Even if there was no light, no matter, no observers, there would still be time in this universe. The notion of “before” the Big Bang makes no sense, because that’s when time itself started.

The perception of the passage of time is relative, and is influenced by the relative speed of the observers, but time itself is an actual inherent property of the universe.

Here’s a good explanation of the whats and the whys: https://phys.org/news/2016-02-what-is-time-and-why.html

Now the question “why is time one of the dimensions of this universe?” Is a good one. It’s possible that the very early universe had more dimensions than the 4 we currently observe. Many forms of String Theory propose that there’s multiple other dimensions in this universe, but they’re wrapped up at a very small scale. Why time was one of the ones that remained at the macro level is an area of continuing investigation.

(Just remember what a “dimension” is. It’s not an “alternate universe” or existence. The idea of “travelling to another dimension” makes no sense.the first 3 Dimensions are exactly what they are when someone describes the dimensions of a book case, or coordinates on a map: length/breadth/height or longitude/latitude/altitude, or position on the x,y,z axis. Time is the 4th dimension in space time. Say you want to meet someone at any location in the universe. You need to know the “where” (x,y,z coordinates) but also the “when” (time). Various versions forms of Sting Theory propose that there’s more types of coordinates (dimensions) at very small scales.)

A few more questions for the Physics experts here.

Why do we exist in a universe with three spatial dimensions (related to existence of orbits apparently).

Is existence of our form/or any intelligent form possible in any other number of dimensions eg would it be possible to experience 4d in some way (this is fascinating to me: what physical conditions allow intelligence or just consciousness)

What is a real physical example of infinity (not sure I've gotten a good answer to its existence outside of maths)

Why do we not remember the future (entropy/psychological arrow of time question and our adaptation to it).

What is consciousness.

EmmetSpiceland wrote: »

We do. Only after it happens, though.

What I mean is why we can't predict the future as easily as we remember the past.

take everything wrote: »

A few more questions for the Physics experts here.

I'm absolutely no expert, but I'll try these and we'll see how it goes...

take everything wrote: »

Why do we exist in a universe with three spatial dimensions (related to existence of orbits apparently).

I don't fully understand the ins and outs of this one, but it seems that the number of spatial dimensions are related to the temperature of the universe. When the universe was a fraction of a second old, it had already cooled to the point of their being the three we have now (before that, when it was hotter, there were more). At this point, a quantity known as the Helmholtz free energy density reached its maximum value. This effectively locked the universe to those three spatial dimensions, and it's stuck with them. To get back to the point of there being more spatial dimensions would require the universe to heat up to a critical point - which it isn't doing as it's constantly cooling down as it expands.

take everything wrote: »

Is existence of our form/or any intelligent form possible in any other number of dimensions eg would it be possible to experience 4d in some way (this is fascinating to me: what physical conditions allow intelligence or just consciousness)

We do experience 4D - time is the 4th dimension, along with width, breadth, and height. So we live in a 4 dimensional universe. Experience of any other dimensions is not dependent on intelligence or form - the limit to the number of dimensions we experience isn't anything to do with us. There is only 4 dimensions to experience. The other dimensions that existed in the very first split second of the Big Bang might sill be around, but if they are, they're wrapped up into an incredibly small size, and because of that tiny size, they have very, very little effect on the rest of the universe. So even if they do exist, they're not something we're going to routinely experience here in the macro world. (But that's not to say that they won't be some day detectable - but the fact that they're not currently detectable puts limits on their maximum size).

take everything wrote: »

What is a real physical example of infinity (not sure I've gotten a good answer to its existence outside of maths)

I'm not sure what kind of example you're looking for. It's not going to be possible to point at something and say "that is infinite", and for you to be able to see that it is infinite - it's always going to conceptual: let's just say there was an infinite pile of apples. It wouldn't look any different to a really, really huge - but finite number - of apples. Even if you travelled in a spaceship for your entire life along the pile, you'd only see a finite number of apples - you'd never witness the infinity. When it is said that a sequence of numbers is infinite, we're able to conceptually show that it has no end, but we can't actually espress the nature of its infinity. I don't think this is a limit of our human minds - I think it's a fundamental property of infinity. It really is endless, and therefore can't be perceived, because perception by it's nature requires a boundary or limit to the thing we're trying to perceive.

It's possible that the universe is infinite in size, and if it is, and it is homogenous (which it should be), then there would be an infinite about of material in it. But there's a limit to the amount of the universe that we can observe - and this brings us back to the speed of light. We can only ever observe the potion of the universe that is within range of the speed of light. It's estimated that this boundary about 13.5 billion light years away. Even if it's not infinite in size, the whole universe is certainly much bigger than the observable part of it. We can really only concern ourselves with the observable part of it, as the rest of it is totally off limits to us an has no effect on us (or us on it). It's also possible that if it is finite, it will continue to expand for infinity. Whether either of these situations are true (that the universe is infinite, or it is finite but expanding infinitely) depends on the topology of the universe, which hasn't been determined yet. But as the observable universe is (by definition) finite in size, it can't contain an infinite amount of anything. So there can't be a physical example of infinity within the (finite) area of the universe that we can observe.

take everything wrote: »

Why do we not remember the future (entropy/psychological arrow of time question and our adaptation to it).

Quite simply, the future hasn't happened yet. Where we are in time, only the past has happened. As time progresses, more and more past has occurred, but the future has never occurred until it its the past. Entropy shows that the arrow of time is external to us, and a fundamental part of the universe. Memories are electrical signals stored in our brains. Our brains don't have any electrical signals for event that haven't happened to us yet - in fact those future events have no bearing, effect or influence on the current universe at all.

As to why we can't predict the future, there is an inherent uncertainly to the universe. Quantum mechanics describes the processes of the universe as probabilistic: There's is a probable chance of something occurring, but it is not guaranteed to occur at any given moment. So whether a quantum event is going to happen or not at any given point of time is uncertain until it happens. The universe basically has random chance built into it at the quantum level. Take a lump of Plutonium 241. It has a half life of 14.4 years. In any given lump of it - regardless of size - on average half the atoms in it will have undergone radioactive decay after 14.4 years. But there is absolutely no way of knowing which individual ones will decay in this time, or exactly when any given individual atom will decay. The best we can possibly say is that the probability of any given atom of Plutonium 241 decaying within 14.4 years is 50%.

There's limits on what we can say about the present too. You cannot simultaneously measure the position and momentum of an electron (or any other particle). This isn't a limitation of the devices or processes used to determine such things, it's a fundamental limit to the existence of these properties (known as Heisenberg's uncertainty principle). So if we can't simultaneously tell where an electron is AND where it is going by observing it in the present, how can we tell where it is going to be in the future? The answer is, it's not possible - it can only be determined within certain limits of probability.

take everything wrote: »

What is consciousness.

I've no idea really. I mean, it can be defined as the state awareness of existence, but how it works, how it came to be, how and why some entities have it and some don't, can it be created artificially, I don't think there's answers to those questions - at least not yet (and there may never be). I'm a materialist, so my suspicion (and position) is that it's an entirely natural process that is a byproduct of a particular organisation of matter, but I don't really have much to back that up. I just think that alternative explanation (that it is something external to physical existence - the result of a god or some other entity) isn't in any way satisfactory, as it just kicks the can down the road, and doesn't explain how they got it. At some point, you have to explain it without recourse to an external entity. Otherwise it's turtles all the way down.

I'm absolutely no expert, but I'll try these and we'll see how it goes...

Thanks for responding

I don't fully understand the ins and outs of this one, but it seems that the number of spatial dimensions are related to the temperature of the universe. When the universe was a fraction of a second old, it had already cooled to the point of their being the three we have now (before that, when it was hotter, there were more). At this point, a quantity known as the Helmholtz free energy density reached its maximum value. This effectively locked the universe to those three spatial dimensions, and it's stuck with them. To get back to the point of there being more spatial dimensions would require the universe to heat up to a critical point - which it isn't doing as it's constantly cooling down as it expands.

Thanks for not dismissing the question with a summary "that's a stupid question", as at least senior level physics student has done when i posed it in the past. Yes someone mentioned the Helmoltz free energy stuff to me in the past as well. I will look into it. I'm not great at Thermodynamics.

We do experience 4D - time is the 4th dimension, along with width, breadth, and height. So we live in a 4 dimensional universe.

Sorry i probably should have said 4 spatial dimensions.

Obviously as you say we experience the universe in 4D as events are 4D.
Or you could extend that and say we experience it in nD, if you include other things as dimensions temperature, colour etc. This begs a question for me as to why time is exalted to a dimension at all and more real than other non-spatial dimensions but that's another story.

Obviously because of the nature of spacetime and how its a real thing (curvature with gravity etc) so it deserves its exalted status i suppose.

But what i really meant to ask was "could we experience/see/process a universe with 4 or more spatial dimensions"

Experience of any other dimensions is not dependent on intelligence or form - the limit to the number of dimensions we experience isn't anything to do with us. There is only 4 dimensions to experience.

OK this i don't really get.
Surely just our biological form is contingent upon how many dimensions our universe has.
This is kind of touching on the Anthropic principle.
But are you saying we could experience any universe in this biological form.
Or are you saying some intelligence (not necessarily biological as we understand biological) could experience any universe with any other number of dimensions.
I don't know about this.

Surely some types of universes (if they exist) can't be experienced/processed by intellligence because they are not conducive to intelligent forms.

I know i might be straying into philosophy here (ontology/epistemology) but its something i wonder about. The connection between the objective reality and the subjective experience of such reality.

The other dimensions that existed in the very first split second of the Big Bang might sill be around, but if they are, they're wrapped up into an incredibly small size, and because of that tiny size, they have very, very little effect on the rest of the universe. So even if they do exist, they're not something we're going to routinely experience here in the macro world. (But that's not to say that they won't be some day detectable - but the fact that they're not currently detectable puts limits on their maximum size).

Fair enough. I find this aspect of physics quite abstruse tbh. Is that string theory you're talking about.

There's limits on what we can say about the present too. You cannot simultaneously measure the position and momentum of an electron (or any other particle). This isn't a limitation of the devices or processes used to determine such things, it's a fundamental limit to the existence of these properties (known as Heisenberg's uncertainty principle).

Oh yeah i understand all that. Thanks. But is that separate to the notions of past and future.

So if we can't simultaneously tell where an electron is AND where it is going by observing it in the present, how can we tell where it is going to be in the future? The answer is, it's not possible - it can only be determined within certain limits of probability.

Could that argument equally say "if we can't tell where it is in the present, how could you know where it was in the future past"

In other word is this a separate discussion to notions of our relationship to and experience of past and future.

Basically I was more talking about the arrow of time. Our psychological arrow of time is determined by the entropic arrow of time from what i understand.

And we are adapted so that we remember the past and not predict the future as accurately. From what i've read it has to do with memory formation and erasure increasing entropy and fitting in with the arrow of time.
Maybe it's not as interesting as i think and maybe it's just obvious that we are just "hostages" to entropy.

I think Sean Carroll has a good bit on the arrow of time (psychological/entropic arrow of time).

I'm not sure what kind of example you're looking for.

A physical example. Or maybe that is an impossibility.

It's not going to be possible to point at something and say "that is infinite", and for you to be able to see that it is infinite - it's always going to conceptual: let's just say there was an infinite pile of apples. It wouldn't look any different to a really, really huge - but finite number - of apples. Even if you travelled in a spaceship for your entire life along the pile, you'd only see a finite number of apples - you'd never witness the infinity. When it is said that a sequence of numbers is infinite, we're able to conceptually show that it has no end, but we can't actually espress the nature of its infinity. I don't think this is a limit of our human minds - I think it's a fundamental property of infinity. It really is endless, and therefore can't be perceived, because perception by it's nature requires a boundary or limit to the thing we're trying to perceive.

Thanks.
So there is a concept of infinity (we use it all the time in maths).
We describe the physical universe with maths that uses infinities all the time.
I just wonder is this sound.
I've done it all my life myself but when i look at someone like Prof. Norman Wildberger (who some might dismiss as a crank) i can't help have doubts and worries.

Even doing Real Analysis in college, I found it an intriguing subject in many ways, but the notion of always being able to go smaller (epsilon delta proofs) left me wondering about stuff like this.

It's possible that the universe is infinite in size, and if it is, and it is homogenous (which it should be), then there would be an infinite about of material in it. But there's a limit to the amount of the universe that we can observe - and this brings us back to the speed of light. We can only ever observe the potion of the universe that is within range of the speed of light. It's estimated that this boundary about 13.5 billion light years away. Even if it's not infinite in size, the whole universe is certainly much bigger than the observable part of it. We can really only concern ourselves with the observable part of it, as the rest of it is totally off limits to us an has no effect on us (or us on it). It's also possible that if it is finite, it will continue to expand for infinity. Whether either of these situations are true (that the universe is infinite, or it is finite but expanding infinitely) depends on the topology of the universe, which hasn't been determined yet.

Of course. No argument there.

But as the observable universe is (by definition) finite in size, it can't contain an infinite amount of anything. So there can't be a physical example of infinity within the (finite) area of the universe that we can observe.

Thanks.
Would it concern you that we use mathematical tools with infinities to describe this all the time.
Maybe it shouldn't i dunno. Haven't fully thought about it but it makes me uneasy :DI'd like to hear your thoughts on this

I've no idea really. I mean, it can be defined as the state awareness of existence, but how it works, how it came to be, how and why some entities have it and some don't, can it be created artificially, I don't think there's answers to those questions - at least not yet (and there may never be). I'm a materialist, so my suspicion (and position) is that it's an entirely natural process that is a byproduct of a particular organisation of matter, but I don't really have much to back that up. I just think that alternative explanation (that it is something external to physical existence - the result of a god or some other entity) isn't in any way satisfactory, as it just kicks the can down the road, and doesn't explain how they got it. At some point, you have to explain it without recourse to an external entity. Otherwise it's turtles all the way down

Cheers.
It is interesting though that consciousness, something truly unique that has qualities so different to everything else (the tool through which the quality of everything else is experienced) is so little understood by us.
Very ironic.

I'll focus on this bit as most of your other questions seem philosophical.

I'm sure they are amenable to some scientific treatment by the experts here. :pac:

The reason why time is considered a dimension alongside space whereas temperature, colour etc. are not is because time and space are strongly related to each other. According to relativity, movement in space changes your perception of time and vice versa.

Yes. Of course spacetime is an accepted thing. Its tied in with gravity which is pretty compeeling. So i get that space and time are more "real" than temperature and colour say. But they are all still just observed physical phenomena that can be promoted to dimensions.

By the way, what do you mean by vice versa here: Are you saying movement in time changes your perception of space?

Also, both space and time would exist and can be defined even if the universe was empty. An empty universe can still have either a finite or infinite spatial size, and time can still pass within it. Temperature and colour, however, need a physical object within the universe to exist for either to have any real meaning.

Is this necessarily true.
How different is the process of measurement of temperature to measure of distance. Or even the perception of colour.
They are both physical phenomena that arguably wouldn't exist without an observer to observe and process.

Are you saying that you're certain the universe would exist without us being there to observe it,

Ultimately all physical phenomena require an observer from what i can see.

No, they aren't. Dimension has a precise meaning in both special and general relativity, partly because of what I already said, and partly because of more complicated reasons. :pac:

Yeah i've no problem with the definition of dimension as used in SR and GR and that we use these 4 dimensions of spacetime to describe General relativity.
Im just talking generally, not about relativity.

Yes. Muons are created at the top of the atmosphere when cosmic rays hit the atmosphere. These muons have such a short lifetime that they should not still exist by the time they reach our detectors on the ground. They do, however, and according to the muon's perspective, this is because the distance between the top of the atmosphere and the ground is shorter than what an observer on Earth would say it is. So the muon's perception of space has changed as they move through time (and space, we should really only be talking about spacetime).

Isn't it just that relative motion at speeds close to c lead to time dilation and length contraction when we observe the other frame

I think you are focusing a bit too much on an observer, probably because we are talking about relativity.

Ah no. I'm not interested in the special relativity argument here. I've done that myself in college.

I think you think i'm talking about the relevance of an observer to SR.
No,no.
I'm just interested in broader aspects of physics like the role of the observer generally.

Like for example, the statement:

A universe exists and is expanding

then space must exist (if it is expanding then it must have a volume) and time must exist (expanding implies changes over time).

Of course all that is true. But an observer is integral to this.
Or are you saying we know for certain a universe (and all there physical phenomena) can exist without directly observing it. That's a pretty bold statement.

However, simply having an expanding universe does not necessitate the need for either temperature not colour.

Is this true.
Colour (essentially EM frequency and our perception of it) and temperature are pretty fundamental physical concepts (thermodynamics would hate to hear you say temperature isn't fundamental :pac:).

Are you talking about an expanding universe without light and energy.
Surely you'd at least have temperature in an expanding universe.

What i'm getting at (in a facetious way) is that when we look at physical phenomena eg distance, time, energy, temperature, these are all just things that have one thing in common (arguably more compelling than space and time being specially intertwined in spacetime and thus seen as proper dimensions). They have an observer that says they are there.