# What is Spacetime?

Discussion in 'Astronomy, Exobiology, & Cosmology' started by Nobody, Oct 22, 2011.

1. ### hansdaValued Senior Member

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I mean , there may be four types of forces but only three types of fields ( magnetic-field , electrical-field and force-field ) .

3. ### OnlyMeValued Senior Member

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Does this mean that you are saying force field when you are referring to a gravitational field? And if so why not just use the accepted terminology, i.e. gravitational field?

5. ### hansdaValued Senior Member

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A particle has a mass and/or charge . These mass and charge are causes of all types of forces and fields .

In the gravitational-field , the cause of force is mass .

Atomic particles also have mass and they generate force/field due to their mass . Do we call these force/field as gravitational-field ?

So, i use the term force-field to generalize any force generated due to mass .

7. ### Pincho PaxtonBannedBanned

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Well don't. We live in a world of human language. You can call an apple a bunch of atoms. Nobody would know what you are talking about. I call the Aether space-time now. You have to be able to communicate.

8. ### hansdaValued Senior Member

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NASA experiment already proves that space-time is a force ; because gyro can measure only force . Gyro cannot measure space , neither gyro can measure time .

9. ### Pincho PaxtonBannedBanned

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They didn't use a Gyro, they used rotational force vectors.

10. ### Gary ARegistered Senior Member

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Spacetime is an "Einstein Aether"

Spacetime is an "Einstein Aether". GR uses tensors, operators and vector matrices that are very similar to those used by fluid dynamicists. So, spacetime is actually a frictionless, massless, viscosity free fluid that can respond to its own density fluctuations. If spacetime becomes dense enough, we call it "matter". So, we have a philosophical question: is space a vacuum or a plenum? It does not matter. The theory of relativity works either way. The closest we can achieve to this in the lab is Helium 4, a liquid phase of helium, close to absolute zero, that shows pretty nearly to the same kinds of properties, which is why it is studied so diligently. It is really freaky stuff!

11. ### hansdaValued Senior Member

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Is there any mathematical equation for your above statement ? ... or... You are considering Einsteins' e=mc^2 .

12. ### wellwisherBannedBanned

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If you look at direct but separate measurements of space and time, space or distance can be measured with a static tool like a meter stick. Time, on the other hand, needs a dynamic tool like a clock, which requires energy. Therefore time is the dynamic aspect of space-time. Space is the passive aspect. GR has mass/energy, while SR has kinetic energy. These impact space-time first through time and then through space, via space-time. It should be called time-space to reflect the priorities with respect to the dynamic connections to GR and SR.

Since the energy of the universe moves from higher to lower energy and since time needs to move forward, this suggests time is the reason for the first law. Space being the passive variable is impacted by the connection within time-space.

Time-space has 3 time dimensions, t0, t1 and t2. T1 is connected to velocity; distance/time while t2 is connected to accelerations such as from force; distance/sec/sec . T0 is connected to mass which provides potential in time even when there is no apparent motion within space-time.

As an example of t0, if we took a snap shot picture of a ball in motion, time has stopped in the photo, so there is no t1 (velocity) or t2 acceleration in the photo. What is left is the potential associated with the static matter; t0. It has potential energy from which time has the potential to emanate even if there is no apparent movement or apparent change.

Space-time is a mental construct as is time-space. Time-space reflects the energy connection associated with time and makes velocity and force special cases of time. SR is all about t0 and t1, while GR is all about t0, t1 and t2.

An interesting application of time-space is connected to explaining the basis for the uncertainty principle, which space-time cannot do. Say we had a baseball pitcher throwing a ball. We take a still picture but with too slow of a shutter speed. What we will get is motion blur. Motion blur will create uncertainty in position. If we knew the momentum of the ball we could calculate its exact position, etc.

Because this is a still picture, we have stopped time down to t0, so only the matter is visible but not apparent movement in space-time. What has happened is there is excess time potential or t1 in the photo, but the still picture does not allow time or t1 or t2 to be expressed. The connection of time to space-time or time-space results in the time potential transferred to distance, via the uncertainty in distance, since distance is passive and not impacted by stopped time. The photo captures the hand-off from time to distance in the film.

The uncertainty principle is basic time-space but beyond space-time.

13. ### hansdaValued Senior Member

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Do you mean to say any of the following three numbered statements ?

1. Space is mass or energy .

or,

2. Time is mass or energy .

or,

3. Spacetime is mass or energy .

Spacetime is the manifold of space and time . This manifold holds all the mass and energy of our universe . Spacetime is the container and mass and energy are the contents of this container . It is obvious that the contents occupy full volume the container . So , total mass and energy of our universe is spread out throughout this manifold of space-time .

14. ### riverValued Senior Member

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space-time , is the measurement of the displacement of an object in space

whether it be light or the Earth

15. ### riverValued Senior Member

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space-time is the description of the movemnt of an object from a certain point in space , to another point in space

16. ### hansdaValued Senior Member

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Then , how 'curvature of spacetime' generates force ?

17. ### riverValued Senior Member

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what curvature of space-time are you referring to ?

18. ### Aqueous Idflat Earth skepticValued Senior Member

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I disagree that spacetime is a fluid, or an aether, or a mass, or an energy, or any other thing declared above that isn't supported generally.

However, I can add a definition that is rarely mentioned, that is supported: spacetime is the vacuum which exhibits the intrinsic free space impedance.

19. ### hansdaValued Senior Member

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As per Einstein's GR , 'curvature of space-time' generates force .

20. ### hansdaValued Senior Member

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What do you mean by your above statement ? What do you mean by intrinsic free space impedance ?

Space-time is mathematically defined by Einstein's Field Equations . So, spacetime must be some sort of field ; curvature of which generates force .

21. ### GrumpyCurmudgeon of LucidityValued Senior Member

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hansda

"As per Einstein's GR , 'curvature of space-time' generates force ."

You've got it backwards, force(in the form of gravity)cause spacetime to curve. There is no force that causes a light beam to bend, to it's perspective it is following a straight line(same goes for a moon). It is that "straight line" that is bent into a curve by gravity.

A light year is a distance light travels in a year. It takes it a year to do so. So if you are looking at a star 100 light years away, you are seeing that star as it was 100 years ago. If that star blows up today, you would still be seeing it as a whole star for 100 years. If our sun was to nova right now, you would not feel any effects or see any difference until 8 minutes from now. Looking out into space(distance)is looking backward in time.

Grumpy

22. ### hansdaValued Senior Member

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Presence of a mass causes 'curvature of spacetime' , which in turn generates force .

A beam of light is bent due 'curvature of space' , which is caused by frame-dragging effect .

'Curvature of space' and 'curvature of spacetime' are quite different . 'Curvature of space' will cause 'curvature of spacetime' but 'curvature of spacetime' may not cause 'curvature of space' .

23. ### hansdaValued Senior Member

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'Curvature of magnetic field' generates magnetic force .

'Curvature of electrical field' generates electrical force .

'Curvature of spacetime' generates gravitational force .

So, 'spacetime' can be considered as 'gravitaional-field' or 'force-field' ; curvature of which generates gravitational force or simply force .