Is spacetime a matter?how can this matter be detected?

Main Question or Discussion Point

Someone told me that spacetime is a matter. I know that matter must be a mass or energy. Is spacetime a matter (mass or energy) , and if it is a mass. why cant we see it? Is it due to the presence of dark matter? If it is an energy. what is its source? The sun?? If it is not mass or energy, tell me what is it. please help and thanks.

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Dale
Mentor
Someone told me that spacetime is a matter.
Someone is wrong.

tiny-tim
Homework Helper
Welcome to PF!

Hi BigBang1234! Welcome to PF!
If it is not mass or energy, tell me what is it.
Spacetime is a space.

It has curvature (that's only "intrinsic curvature", it doesn't mean that it's contained in some bigger space in which it has a physical curvature).

It has nothing but curvature.

qsa
Someone told me that spacetime is a matter. I know that matter must be a mass or energy. Is spacetime a matter (mass or energy) , and if it is a mass. why cant we see it? Is it due to the presence of dark matter? If it is an energy. what is its source? The sun?? If it is not mass or energy, tell me what is it. please help and thanks.
In GR space geometry is shaped by matter, but in some quantum gravity theories space and matter can be described in terms of each other

http://arxiv.org/PS_cache/arxiv/pdf/1006/1006.2230v2.pdf [Broken]

Abstract. In this paper we will discuss the question how matter emerges from
space. For that purpose we consider the smoothness structure as underlying
structure of the spacetime manifold. The smoothness structure depends on an
infinite structure – the Casson handle – representing the failure to smoothly
embed a disc without self-intersections (immersed disc). By using the Weierstrass
representation, we are able to show that the immersed discs are represented by
spinors fulfilling the Dirac equation and leading to a mass-less Dirac term in the
Einstein-Hilbert action. Between the immersed discs, there are “connecting tubes”
which are realized by an action term of a gauge field. Both terms are genuinely
geometrical and characterized by the mean curvature of the components of the
Casson handle. We also discuss the gauge group of the theory.

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I love to try to answer this question in part because it's interesting and also because every time we discuss it and I say "Spacetime IS something", meaning "it sure SEEMS like something, lots of the gurus here get apoplectic...that is excitedly angry .... because its not a conventional answer...but we can describe some attributes of spacetime that bring home how interesting it is.

Tinytim's post probably reflects conventional, current, science. But a lot that is conventional science is incomplete. You could also call spacetime a model:
http://en.wikipedia.org/wiki/Spacetime
meaning how we choose to represent space and time, and the discussion has other interesting points to make as well.

Spacetime is conventional three dimensional Eucledian space plus time (not a very satisfying answer,of course). Even if someone said "space is a matter" nobody knows what matter is either, any more than we know what time or gravity is.

Suggest you search the forums here with "what is spacetime",,,you'll finds lots of threads (discussions).
Seems like space requires time, and that spacetime IS actually something with these among its characteristics:
measured distances and elapsed times depend on your velocity and position,
it expands and that expansion is accelerating,
it seems to have horizons,
it can curve (change shape due to mass,energy or pressure)
always seems to have quantum fluctuations (quantum foam, even at zero degrees absolute)
maybe dark energy (we sure don't know what THAT is either,
some symmetries,
maybe some singularities (big bang, inside black holes),
an interval (a combination of space and time, see spacetime interval in the above reference).

Another way to think of spacetime is that it apparently originated from a big bang...in that view, some extremely high unstable entity (a bang) gave birth to mass, energy,time,distance(space) and an expanding universe. But why THESE particular entities popped out, and not others or not in different combinations, nobody knows.

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Wouldn't it be more prudent to determine how energy comes from space since it is the fundmental makeup of all matter? The only connection we currently have between space and matter is relativity and it would seem to need a lot more in the theory. You would prob also expect such a thoery to explain particle pair creation and annihilation in empty space.

But energy is not space, and is only more like a medium it travels through. I don't see anywhere in the paper where the connection we know of between space and energy is even used (SR).

qsa
Wouldn't it be more prudent to determine how energy comes from space since it is the fundmental makeup of all matter? The only connection we currently have between space and matter is relativity and it would seem to need a lot more in the theory. You would prob also expect such a thoery to explain particle pair creation and annihilation in empty space.

But energy is not space, and is only more like a medium it travels through. I don't see anywhere in the paper where the connection we know of between space and energy is even used (SR).

Particles are modeled as fields, and the word "emerge" has more a meaning of equivalence(in description) than the same. Particles are also "equated" with energy . There is no accepted theory of modeling particle as photons(energy). only, there is the old "electromagnetic mass" theory by Lorentz which is not accepted yet, maybe in the future ,who knows.