Understanding Spacetime: Exploring Its Reality and Conceptualization in Physics

[maverick_starstrider]

There are dozens of interpretations of quantum mechanics (see http://en.wikipedia.org/wiki/Interpretations_of_quantum_mechanics#Comparison)

 

[maverick_starstrider]

If you think millions of universes constantly branching off from each other isn't wildly different from one where an observer can cause the collapse of a wavefunction then that's ok, but I find it strange. As far as I can see, there is either one universe or there is more than one. We may not know how many there are (and may not be able to ever find out), but that doesn't change this fact. A logical positivist might say the distinction is meaningless, but I can't agree.

Yes but the point is if pragmatically one can never tell the difference then what's the point in asking about the nature of it since no one does or ever can have the answer. Wanting and answer to a question which can never be answered is one thing. Expecting an answer is something entirely different.

 

[madness]

How do we distinguish between what cannot be known now and what can never be known? It is conceivable that one day we may be able to prove the existence of these other universes, so it seems a bit of a copout to say there is no point in asking the question. I also think considerations such as the anthropic principle might lead one to believe one interpretation is more sensible than the other, even if they don't offer scientific proof. I object to the logical positivist assertion that such questions are meaningless. We may not know and we may never know but I still view it as a meaningful question.

 

[madness]

And I also think my original question was meaningful. Look at the post "can man transcend the fabric of space and time?", if you accept the relational view of space and time then the whole question is almost meaningless.

 

[Kenny_L]

As far as I can see, there is either one universe or there is more than one. We may not know how many there are (and may not be able to ever find out), but that doesn't change this fact. A logical positivist might say the distinction is meaningless, but I can't agree.

The way I see it is ... there is one universe, which is the collection of the whole lot. When you think of many worlds...then that's alright, because that's a subset of the universe. If somebody thinks there's many 'universes', then something's wrong with their definition of universe, because universe means everything...no matter where there are lots of branches/dimensions etc... universe includes all of that as well.

 

[Crosson]

The way I see it is ... there is one universe, which is the collection of the whole lot. When you think of many worlds...then that's alright, because that's a subset of the universe. If somebody thinks there's many 'universes', then something's wrong with their definition of universe, because universe means everything...no matter where there are lots of branches/dimensions etc... universe includes all of that as well.

Obviously the universe does not include everything, since there isn't even one circle to be found in the entire thing.

To me the universe is equal to the set of matter that an eternal observer on Earth could conceivably share a photon with.

 

[Crosson]

And I also think my original question was meaningful. Look at the post "can man transcend the fabric of space and time?", if you accept the relational view of space and time then the whole question is almost meaningless.

Yes!

Critiques of these kind can be found in the latter work of Ludwig Wittgenstein. In a nutshell, his argument is that we get into conceptual trouble when we take abstract nouns like space and time excessively far away from their ordinary use in the language.

 

[Kenny_L]

Obviously the universe does not include everything, since there isn't even one circle to be found in the entire thing. To me the universe is equal to the set of matter that an eternal observer on Earth could conceivably share a photon with.

Nobody said that it required a circle...which is only 2 dimensional thinking. The universe includes everything there is, whether you can see it or not...whether you know about it or not. It includes everything. It even includes your eternal observer and your protons.

 

[Crosson]

The universe includes everything there is, whether you can see it or not...whether you know about it or not. It includes everything.

Then it includes all the circles right? Isn't each circle a thing?

 

[Kenny_L]

Then it includes all the circles right? Isn't each circle a thing?

Yes...a circle is a 'thing' too... and our universe includes all circles.

 

[madness]

Perhaps in the sense that the universe includes us, and the idea of a circle is in our minds, the universe includes all circles. But it doesn't include perfect circles in a physical sense.

 

[Kenny_L]

Perhaps in the sense that the universe includes us, and the idea of a circle is in our minds, the universe includes all circles. But it doesn't include perfect circles in a physical sense.

It does indeed include 'perfect circles' too...it includes whatever you (or anybody) can think up. Whatever idea you have ... it's part of the universe as well. Because whatever you think of is a subset of the universe ... even the dreams/imagination/thoughts you have...all part of the universe.

 

[shamrock5585]

Obviously the universe does not include everything, since there isn't even one circle to be found in the entire thing.

To me the universe is equal to the set of matter that an eternal observer on Earth could conceivably share a photon with.

where does circles have anything to do with anything... a perfect circle does not exist because pi is a never ending decimal... what does that have to do with the universe?

ok well no observer can share a photon with a black hole because black holes keep all the photons to themselves (greedy bastards) haha... does that mean black holes are not part of the universe?

 

[Crosson]

where does circles have anything to do with anything... a perfect circle does not exist because pi is a never ending decimal... what does that have to do with the universe?

Perfect circles do not exist? I will show one to you:

$$S = \{(x,y)\in \mathbb{R}^2 | x^2 + y^2 = 1\}$$

I suppose you might say that that is merely a sentence, or a configuration of liquid crystals, intended to convey the idea of a circle. But then you have admitted that the idea of a circle exists! And since the universe includes everything that exists, according to you, then it must contain the idea of a circle, so please show this to me.

ok well no observer can share a photon with a black hole because black holes keep all the photons to themselves (greedy bastards) haha... does that mean black holes are not part of the universe?

An important method for detecting black holes uses gravitational lensing, I consider this to be exchanging a photon with a black hole, since the black hole has a direct influence with the photon I detect. As far as what is inside the event horizon, it does not bother me to say that what goes on in there is not a part of the universe.

 

[shamrock5585]

Perfect circles do not exist? I will show one to you:

$$S = \{(x,y)\in \mathbb{R}^2 | x^2 + y^2 = 1\}$$

I suppose you might say that that is merely a sentence, or a configuration of liquid crystals, intended to convey the idea of a circle. But then you have admitted that the idea of a circle exists! And since the universe includes everything that exists, according to you, then it must contain the idea of a circle, so please show this to me.



An important method for detecting black holes uses gravitational lensing, I consider this to be exchanging a photon with a black hole, since the black hole has a direct influence with the photon I detect. As far as what is inside the event horizon, it does not bother me to say that what goes on in there is not a part of the universe.

but you are not actually exchanging a photon with the black hole... you are exchanging with photons emitted from something else that the black hole interacted with and then you are a third party.

you said it yourself... the IDEA of a perfect circle... I am saying in nature does a perfect circle exist?... no

 

[Crosson]

I agree that perfect circles aren't found in nature, that's why it is wrong of you to say that the universe contains everything that exists.

you are exchanging with photons emitted from something else that the black hole interacted with and then you are a third party

I think we agree. The gravitational field outside the black hole belongs to the universe, since I can receive photons that have presumably "bounced off" the gravitons that constitute that field. But whatever is inside the event horizon is no longer a part of this universe!

 

[Kenny_L]

I agree that perfect circles aren't found in nature, that's why it is wrong of you to say that the universe contains everything that exists.

It depends on what you define as nature. Because the subject of the universe, that exists in your mind, or somebody else's mind, contains a sub-universe with the perfect circles. And nature is nature ... if it exists in your mind, then that's nature too. So perfect circles exist, or can exist in nature.

 

[shamrock5585]

yes but i can also picture a unicorn in my mind... does that mean a unicorn exists in nature?

 

[shamrock5585]

But whatever is inside the event horizon is no longer a part of this universe!

a black hole is most likely a giant extremely dense amount of mass... which would create an enormous amount of gravity... this is a simple explanation of what a black hole is... or it could be some magical gateway to another universe... but usually in science we look for the simplest explanation

 

[cristo]

yes but i can also picture a unicorn in my mind... does that mean a unicorn exists in nature?

No, it doesn't.

Besides, this is way off topic. How about we focus more on discussing the main point of the thread: whether spacetime is a real entity, or a mathematical construct.

 

[Kenny_L]

yes but i can also picture a unicorn in my mind... does that mean a unicorn exists in nature?

Yes...of course it exists in 'nature', because you're able to 'synthesise' it in one form or another. And in this case, you have it in your mind, which would be yet another dimension...subset of the universe.
==

And...back to space and time...these are words ... words that we use/define a system that involves length/size/distance etc... and something for logging events from/between one 'moment/instant' to another.

 

[shamrock5585]

yes but wouldn't just the THOUGHT of a unicorn exist... the unicorn itself would not "exist"


PS... actually kinda funny but i a couple of weeks ago in the news some people submitted a picture of a rare deer with one horn and the horn was in the center of its head haha

 

[Kenny_L]

yes but wouldn't just the THOUGHT of a unicorn exist... the unicorn itself would not "exist".

Of course it exists! It exists in that dimension, in your mind. And I'm sure that if our technology were good enough today, we'd be able to tap into that 'dimension', and be able to see roughly what that unicorn looks like, and what it can do. If it exists in your mind...it is also part of 'nature'.

 

[Moridin]

concept of unicorn =/= unicorn

 

[shamrock5585]

i guess we could argue this all day and there really is no answer, but your mind isn't actually a different dimension... realistically your brain has a processor and memory and obviously a bunch of other junk... but your "processor" stores the "thought" of a unicorn in your memory chemically and its the thought that exists "in reality" which is the definition of existing in the first place (reality) so the "thought" exists to represent the unicorn which itself does not exist. Infinity does not really "exist" but we can represent it and use it. Same thing with immaginary numbers.

 

[Kenny_L]

i guess we could argue this all day and there really is no answer, but your mind isn't actually a different dimension... realistically your brain has a processor and memory and obviously a bunch of other junk... but your "processor" stores the "thought" of a unicorn in your memory chemically and its the thought that exists "in reality" which is the definition of existing in the first place (reality) so the "thought" exists to represent the unicorn which itself does not exist. Infinity does not really "exist" but we can represent it and use it. Same thing with immaginary numbers.

Yes...but the thing is...how do you know if you, yourself, might be a box, hooked up to a virtual reality system, where everything you see, and 'do' are simulations? But, if the simulations are so 'real' where you, yourself, can't even tell whether you're actually a box, then there's no difference between one form of existence or another. It becomes existence...or 'real'...and even thoughts of something like a unicorn become 'real'...or existing...even if it exists 'inside' your 'head'.

 

[shamrock5585]

haha the good old theory from the matrix movie... don't you think if some living creature made up a virtual reality system there would be flaws in it and one of the 6.5 billion ppl on the planet would have experienced a side effect and figured it out or something? I mean for all our existence we have been providign answers for where we came from and how the world works and this virtual reality just happens to be perfect?

 

[robheus]

I don't think that existential philosophical questions should be discussed in the context of physics.
We are best to avoid bickering philosophy and semantics.

The context of the subforum IS however PHILOSOPHY, so why not?

 

[Evo]

The context of the subforum IS however PHILOSOPHY, so why not?

Because the science guidelines hold in this forum. If a thread wanders too far away from known science, it will be closed. This thread has already been closed once and it's not doing all that well. Let's all follow cristo's advice and limit this discussion to whether spacetime is a real entity, or a mathematical construct.

 

[robheus]

About space time existence:

In Newtonian physics, space and time are merely distance relations between objects/events.

In General Relativity though, space time posseses properties, like curvature.
Objects in space time are causing space time (more mass in one place->more curvature) and also a curved space causes objects to follow curved trajectories.

This at least shows that in GR spacetime is more intimately related to matter, and is not just "emptiness". But also it is not an ether (a fluid medium).

Spacetime does not exist apart from matter, and neither does matter exist apart from spacetime.

 

[starkind]

Just curious. What makes you think matter exists?

 

[madness]

Just saying that in GR spacetime really exists doesn't make it true. I don't see that the same old relational view of space and time can't be kept when the transition to Einstein's GR is made. Instead of saying "spacetime is curved", you could say "objects follow a curved trajectory", which I think is a more sensible conclusion to draw from the evidence. How does any of this show that spacetime is not just "emptiness"? Why does it imply that spacetime doesn't exist without matter?

 

[oldman]

Just saying that in GR spacetime really exists doesn't make it true. I don't see that the same old relational view of space and time can't be kept when the transition to Einstein's GR is made. Instead of saying "spacetime is curved", you could say "objects follow a curved trajectory", which I think is a more sensible conclusion to draw from the evidence. How does any of this show that spacetime is not just "emptiness"? Why does it imply that spacetime doesn't exist without matter?

By describing the trajectory of objects, rather than saying 'spacetime is curved' you are taking a welcome step towards an operational definition of spacetime. I strongly support such a concrete approach.

But keep in the back of your mind that spacetime is an abstract mathematical 'space'. Its metric is defined with space and time coordinates, based on the concept of number. And numbers are abstractions fundamental to mathematics. Mathematics itself is ultimately nothing more than an extraordinarily powerful language that clever folk have invented and other clever folk use to quantitatively describe nature.

In the end I believe it's simpler to detour past such complications and take an operational approach, as you have done.

 

[robheus]

Just saying that in GR spacetime really exists doesn't make it true. I don't see that the same old relational view of space and time can't be kept when the transition to Einstein's GR is made. Instead of saying "spacetime is curved", you could say "objects follow a curved trajectory", which I think is a more sensible conclusion to draw from the evidence. How does any of this show that spacetime is not just "emptiness"? Why does it imply that spacetime doesn't exist without matter?

In GR it is mass that causes spacetime curvature. But this works also the other way around in that mass is the result of curved spacetime.

The argument that spacetime is not really empty (as in Newtonian physics) because there are virtual particles in all parts of space, and as we assume also, contains dark energy.
So this makes the current viewpoint on what spacetime is different as in the Newtonian physics.

 

[oldman]

In GR it is mass that causes spacetime curvature.

Agreed.

But this works also the other way around in that mass is the result of curved spacetime.

No. Why should this be so?