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the speed of light question
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Moderators, Recreation & Hobbies Moderators, Science, Health & Environment Moderators, Technology & Internet Moderators Posts: 90,730 Mod ✭✭✭✭
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Why is there a Maximum Speed of Light ? why can it not go faster or even as fast as it damn well pleases ? ?
Blame electricity and magnets and Maxwell. He got the gig to check out the "F*cking Magnets, How Do They Work?" or rather the "electricity makes magnets ?? WTF , explain !" one.
So Maxwell goes off and does theorising and maths from first principles and does up equations for electricity fields and magnetic fields and how a collapsing field in one can generate a field in the other. Permeability and permittivity and all that. Job done.
But he then figured out that those collapsing fields could keep oscillate if they propagated as a wave. So back to the maths, and when he worked out the speed the wave travelled at it looked very, very surprisingly familiar.
https://web.pa.msu.edu/courses/2000fall/phy232/lectures/emwaves/maxwell.html
IMHO Mr Maxwell came up with the first really big unifying theory of physics.
We later learnt that apart from gravity and radioactivity, most of the interactions we have with the real world are with electrons and photons. You don't touch atoms. Your electrons and their electrons repel each other which is what you feel. Chemistry is mostly electrons jumping from one orbit to another and that requires capture and/or emission of photons.
It led to better motors and wireless communication, in fairness people were already using light but still...0 -
I'm absolutely no expert, but I'll try these and we'll see how it goes...
Thanks for respondingI 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 thisI'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.
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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.0 -
take everything wrote: »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.
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:By the way, what do you mean by vice versa here: Are you saying movement in time changes your perception of space?
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).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.
I think you are focusing a bit too much on an observer, probably because we are talking about relativity. If I simple state the following is true:-
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). However, simply having an expanding universe does not necessitate the need for either temperature not colour.0 -
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No, time dilation occurs at all speeds, not just close to c.
Eh yeah i know it occurs at all speeds.
I know SR is a better description of nature than Newtonian mechanics with Newtonian Mechanics a limiting case where speeds are a fraction of c.
Where the v squared over c squared in gamma is so close to zero that gamma is practically one hence practically no time dilation or length contraction.
It feels like you're responding to another poster.
I'm not talking about or interested in SR. I gave a rough explanation of it in the thread already talking what you are talking about. I'm agreeing with you.No. I am saying that if we assume that a universe does exist, then space and time must also exist.
Without being cheeky, the act of assumption is done by an observer.
Space and time to me only have meaning after measuring them.However, the concepts of temperature and colour do not have to exist.
Aren't these concepts inextricably linked to physical phenomena.
A universe without temperature. Is that even possible. A thermodynamics expert might clear that up. But i always thought temperature was inextricably linked to internal energy. So no temp would mean no internal energy. Is that possible for a universe with stuff in it.
Colour (a biological processing of EM frequency) etc etc.A universe can theoretically exist without particles or light and therefore without the concept of temperature or colour.
So you're saying light is needed for temperature. That sounds wrong to me tbh. I would have thought internal energy is needed for temperature.
But either way, a universe without light or energy?
But with space and time?
Never heard of something like this. Is this possible anyone know.
Either way it would never be measureable (without light etc) and arguably non-existent.
Why does there seem to be a presupposition that space and time are more important physical phenomena than all other physical phenomena. That a universe with just space and time can exist but not just temperature and say energy can exist.Yes. But that is not what we mean by a dimension in physics. Space and time are not defined as dimensions only because they can be measured, we're certain they exist etc.
Yeah i know this. The 4 dimensions of spacetime are conventional dimensions. But are they more certain than other perceived and measured phenomena? :pac:. By the quoted statement, "we know they exist", all the other things we mentioned (that "we know exist") are dimensions. But i'm not saying that really. You seem to be arguing more strongly for it here. Im only half messing about them being dimensions :pac:
Ah i'm again being a bit facetious in all this. You can put anything into the dimension of a space in Linear algebra :pac::p0 -
take everything wrote: »Eh yeah i know it occurs at all speeds.
I know SR is a better description of nature than Newtonian mechanics with Newtonian Mechanics a limiting case where speeds are a fraction of c.
Where the v squared over c squared in gamma is so close to zero that gamma is practically one hence practically no time dilation or length contraction.
It feels like you're responding to another poster.
No, I was responding to your statement of "relative motion at speeds close to c lead to time dilation".take everything wrote: »Without being cheeky, the act of assumption is done by an observer.
Space and time to me only have meaning after measuring them.
I was not referring to measuring or observing anything, I was referring to a thought experiment. We know that stars were born and have since died since before life existed on Earth, but according how you are thinking, they didn't because no one was around to observe or measure them?take everything wrote: »Aren't these concepts inextricably linked to physical phenomena.
Yes, which is one of the reasons they are not dimensions. We can say that an object (or system) has an energy of x, a length of x, a temperature of x etc., but it doesn't make sense to say it has a time of x or a space of x. Dimensions do not describe a quality of a particle (or system).take everything wrote: »A universe without temperature. Is that even possible. A thermodynamics expert might clear that up. But i always thought temperature was inextricably linked to internal energy. So no temp would mean no internal energy. Is that possible for a universe with stuff in it.
I am an astrophysicist, I am such an expert.
Ignoring quantum fluctuations (which we are not talking about), an empty universe would not only have no temperature or internal energy but there would no benefit in defining what something called temperature or energy is.take everything wrote: »So you're saying light is needed for temperature. That sounds wrong to me tbh. I would have thought internal energy is needed for temperature.
No, I did not say that. Have a re-read.take everything wrote: »There seems to be a presupposition that space and time are more important physical phenomena than all other physical phenomena. That a universe with just space and time can exist but not just temperature and say energy can exist.
No, not more important, just more fundamental.0 -
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