Space expanding? or perhaps time slowing...

[BigMoosie]

Thanks for those sources, I am pretty sure with the question about rotation, just wasn't thinking straight on the day I posted it.

 

As for space expanding. I realise how it is supposed to be happening and understand the theory behind it. But all I am saying is that it might necessarily not have to be true. If time was speeding up or the speed of light decreasing it would explain things just as perfectly. We have equations that relate space and time, when we notice things changing like the space expanding we can look back to these equations and realise that that may not be the factor that is changing but other parts of out equations might be making the same observations.

 

For example, if I see something increase in size by double, it may not be that it increased but rather that I shrunk. Also if galaxies appear red shifted, then it is possible that time is faster now than when it was emitted thus making the oscillations of the wave look like they take longer than other light waves from closer galaxies. Does nobody follow me?

[Spyman]

I follow You, but I am not educated in relativity so I can't say for sure.

 

My guess: Light always propegates at c, so if time would speed up so would light, thus no redshift.

 

But it might be considered as an acceleration which could cause the redshift.

 

Also when the Universe was older it was also less expanded which would place the emitter in a higher gravitational potential, which could cause a part of the redshift we see.

[J.C.MacSwell]

The pendulum answer by swansont is correct.

 

.

 

Then the Universe could have a rotation?

[BigMoosie]

All the matter in the universe might be orbiting the center of mass, but any such rotation is measurable. I guess what I was getting confused about is that I was considering the body an entity with no extent such as a point (which I presume for rotation would not be measureble). But when you have a sphere rotating, imagine the effects of somebody living at the equator, they would experience less gravity than somebody at the poles because they are thrust outwards by the centrifugal force.

[BlackDog]

The pendulum answer by swansont is correct.

 

Some' date=' threads You and BigMoosie may want to read:

 

[b']Is rotation absolute or relative ?[/b] http://www.scienceforums.net/forums/showthread.php?t=11470

 

How is space expanding ? http://www.scienceforums.net/forums/showthread.php?t=9729

 

Space expanding FTL http://www.scienceforums.net/forums/showthread.php?t=9693

 

There are a lot of threads with information, most questions have already been asked and answered.

 

Use the search function to find more...

 

oops... sorry i didn't notice that "physics expert" title under swansont! (how dare i am to think he is wrong... stupid me).

 

thanks spyman. okay, now i understand that with a focault pendulum, it's possible to tell whether something is spinning or not. so that means spinning is absolute! that means earth's rotation on its axis does not affect the relativity of moon's orbit in respect to earth. but why is spinning absolute and not relative? now i'm more confused. should have studied physics (would have failed though). ah... going back go google.

 

 

-shami

[BigMoosie]

Actually I heard somewhere that it relativity predicts an undetected (as of yet) ever so slight extra warp in space when heavy objects spin, but I'm sure that is just trivial.

[ydoaPs]

there is actually a satellite in orbit doing an experiment to detect that right now.

[ydoaPs]

http://www.scienceforums.net/forums/showthread.php?t=3700

[BigMoosie]

I know, stupid NASA has poured millions of dollars of research into this and now a smaller group with a smaller budged has found out that they can test the theory simply by studying the impulse of two closely orbiting pulsars.

[Spyman]

Then the Universe could have a rotation?

With respect to what ?

 

A planet rotates once per day. And it has a moon that orbits it across its equator once per day and the moon itself rotates once per day so it always faces the planet.

 

Imagine there are no other objects in the universe apart from these two bodies.

I don't think the Universe is rotating in the example given' date=' only the bodies within it.

 

What revolution do You think the Universe have in the example ?

(The same as the Planet, the Moon, the Moons orbit, an average or something else ?)

 

In the example given, everything in the universe was rotating (wrt what I do not know). Didn't the thought experiments when GR was developed assume that, in this type of case a Foucault pendulum would not read the "rotation" such as it is?

If a body is revolving around the center of mass with the same revolution as the total mass of Universe it should still be measureable.

 

If space-time also is revolving then I can agree that it won't be measureable. But what would space-time revolve with respect to if everything inside is revolving with it ?

 

why is spinning absolute and not relative?

Spinning can be considered an acceleration because speed is moved from one dimension to another.

Forward & Reverse is one and Left & Right is another, (Up & Down is the third and Time the fourth).

To complete an circle You move Left, Forward, Right, Reverse with the same decrease of speed in the ongoing direction as increase in the next.

[J.C.MacSwell]

What does current theory say about this? If everything in the universe was, on average, rotating would a foucault pendulum be dragged around with it or not?

 

If gravity and inertia are locked in step the way they appear, doesn,t the mass distribution and movement effect both inertia and gravity and through the same means?

 

I don't know if this is right, but I think this is basically mach's idea.

 

If this is not right then is space somewhat independant of mass?

[Severian]

What does current theory say about this? If everything in the universe was, on average, rotating would a foucault pendulum be dragged around with it or not?

 

In principle a foucalt pendulum would demonstrate a rotation, but in practice how fast it would rotation would depend on how quickly the universe where rotating. I would suspect it would be too slow to measure.

 

More significantly, a rotation would be identical to an outward force eminating from the centre of rotation (since you have no external reference). I am fairly sure that this would be seen in the data if it were in any way sizable. Indeed, there doesn't even seem to be a centre in the data, nevermind a force coming from it.

[BlackDog]

Spinning can be considered an acceleration because speed is moved from one dimension to another.

Forward & Reverse is one and Left & Right is another' date=' (Up & Down is the third and Time the fourth).

To complete an circle You move Left, Forward, Right, Reverse with the same decrease of speed in the ongoing direction as increase in the next.[/quote']

 

okay i understand the acceleration part. and (please see if i'm getting it right) since acceleration can be experienced by any two observes even if they are at different velocity, acceleration is not relative with their velocities. but it still gives me a head spin to imagine a ball spinning in an empty universe without having no "absolutely space" (that newton mentioned), in the case of circular motion. so what are we comparing the acceleration with? i guess the previous velocity of the object? but then don't these velocities themselves need reference frames or something to compare each of them with?

 

 

-shami

[Spyman]

so what are we comparing the acceleration with?

Inertia

Inertia is the tendency of any state of affairs to persist in the absence of external influences. Specifically' date=' in physics, it is the tendency of a body to maintain its state of uniform motion unless acted on by an external force.[/quote']http://en.wikipedia.org/wiki/Inertia

 

Imagine You are standing, (boots firmly looked), on a thin but large CD-disk flying through space with constant speed, release a ball from Your hand, it will continue to fly beside You.

(Neglecting the small gravity from the disk, You and the ball.)

 

Now if the disk would be accelerating forward or rotating where will the ball end up ?

It will continue in a straight line with the constant speed it had when released like in the first example.

But since You are accelerating, You are not going in a straight line with constant speed, so from Your point of view the ball will take off in a strange direction.

 

Velocities needs reference frames to be measured relative but accelerations is due to forces that can be measured compared to Inertia.

[BlackDog]

so is it fair to say that in an empty universe with only one object, the object can't be moving along a straight line, so velocity cannot be defined, yet it can have acceleration? you see, the example you gave me also include two objects, me and a ball, to explain the effect of acceleration. still seems very weird to me.

 

sorry for keep asking questions on the same subject.

 

 

-shami

[Spyman]

in an empty universe with only one object

If it was only one single body then that single body and the space around it would be the Universe, and I don't think the Universe can either move or accelerate.

 

But, if we say that we are in an empty part of the Universe, without being able to see or measure anything else then:

the object can't be moving along a straight line, so velocity cannot be defined, yet it can have acceleration?

The object can be moving but since there is no reference the speed can't be measured.

 

If You close Your eyes in a car moving in a straight line, are You able to sense the speed of the car ?

 

Now if the car takes a hard turn or the driver hit the brakes, will You feel the forces ?

 

the example you gave me also include two objects, me and a ball, to explain the effect of acceleration.

Well, there has to be someone with some cind of equipment to measure both speed and acceleration. A single body can't do anything else than ceep it's inertia, it's not conscious and have no desire/tools/senses to aquire knowledge.

 

However, the forces would still be acting on the body, if for an example the rotation is rapid enough, the body should be flung apart.

 

sorry for keep asking questions on the same subject.

Don't be, it's the only way to find out when confused.

(And my explanations may not be the best.)

[BlackDog]

i think i didn't ask the question right. my question is, is it possible to define acceleration with only one object in the universe? lets suppose that object is an atom.

 

the reason for my question is, if it'd be possible to define acceleration with only one object, i would understand that acceleration is not relative. if it cannot be defined without two objects, it must be relative, right?

 

of course i understand if we have two objects, such as the pendulum and earth, there would be acceleration. even in an universe with two objects, if we move the objects away from each other, we must have motion, and as their relative motion goes from 0 to x velocity, we would have acceleration. but what if we don't have two objects?

 

 

-shami

[BigMoosie]

Depends on how the accellaration is being created. If it is gravity then it will be not noticable because all the instruments will be moving at the same speed as the body. If it is accellaration from its own creating then yes you will notice accellaration, as accellaration can only occur if the body is expelling some kind of matter in the opposite direction.

[Spyman]

BlackDog: A single object still needs a force for it to accelerate but not to maintain speed.

 

BigMoosie: Even if it's gravity there would be tidal forces which could be measured.