Space expanding? or perhaps time slowing...

[BigMoosie]

If the fabric of space is expanding then the distances between galaxies is expanding, but this must also mean that the galaxies themselves are expanding. If this is so, then isnt that the equivalent of space staying constant and the ratio of light-speed to time changing? We presume that space is expanding because galaxies are moving apart too fast, but what if the reason they appear to be moving was just because the light was emmitted at a date when time was slower, and now that it is faster the light reaches us and it appears to be severely red shifted. After a certain distance time would have been too slow for it too have reached us yet explaining why it is unobservable.

Please let me know if this is flawed, and also what observations bring scientist to conclude that space is expanding.

[BigMoosie]

Let me know if I worded that badly. In the meantime I have another question.

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. It would appear that they are both stationary; not spinning or moving. In that situation one on the planet would expect the moon to fall, so would I, isn't everything relative?

[J.C.MacSwell]

Once per day with respect to what?

[BigMoosie]

That detail is not important, the bodies just have to rotate respective to each other.

[swansont]

Let me know if I worded that badly. In the meantime I have another question.

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. It would appear that they are both stationary; not spinning or moving. In that situation one on the planet would expect the moon to fall' date='[/color'] so would I, isn't everything relative?

 

 

You can tell if you're rotating. Some bright sould would eventually notice what happens with a Focoult pendulum.

 

_{(and what's the deal with with the letter color spectrum? Isn't that incredibly time-consuming?)}

[BigMoosie]

Oh, yeah, I wasnt thinking properly about inertia and that. As for the colour spectrum... what kind of fool would do that manually? I spent 5 minutes writing a script to do it for me, now I can type in colour everywhere I go!

[revprez]

Can you stop using it? You're making it difficult for people who just want to reply to part of your posts.

 

Rev Prez

[BigMoosie]

Sorry, I didnt think about that, it has been too long for me too edit the above posts but I edited that one... to quote me, just select the text on your screen and manually enter a:

 

[/b]]...

[J.C.MacSwell]

You can tell if you're rotating. Some bright sould would eventually notice what happens with a Focoult pendulum.

 

_{(and what's the deal with with the letter color spectrum? Isn't that incredibly time-consuming?)}

 

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?

[BigMoosie]

If space got larger, I would expect every single particle to get larger also, is there proof that the galaxies aren't expanding themselves? It would be such a small increase on this scale so I wouldn't expect any measurements to be able to detect that.

 

If the galaxies arent getting larger with space, then wouldn't that mean that there is new energy in the form of GPE ?

[BigMoosie]

Ok, just a basic question here, no matter what my reference frame, can I always double my perceived speed?

[swansont]

Ok, just a basic question here, no matter what my reference frame, can I always double my perceived speed?

 

The question is poorly framed. What do you mean by "no matter what reference frame?"

 

There will always be a reference frame with which you may double your speed, since you can always define a reference frame that is travelling at less than c/2 with respect to you. But you cannot say this about any arbitrary reference frame.

[BigMoosie]

If I am going at c/2 then I try to double my speed, I will think it gets doubled but in reality it is now going 3c/4 or similar ?

[swansont]

If I am going at c/2 then I try to double my speed, I will think it gets doubled but in reality it is now going 3c/4 or similar ?

 

If you are going at a speed of c/3, it is possible for you to go at 2c/3, with respect to some frame A.

 

The velocity addition formula comes into play when there is an additional observer/frame. If you were travelling at c/3 and doubled your speed to 2c/3, with respect to frame A, you would not have doubled your speed with respect to some other frame B that is not at rest with respect to either you or A. That's why I said your original question was poorly framed - it did not distinguish between a specifically chosen frame or an arbitrary frame.

[BigMoosie]

But what if I try to double my speed at 2c/3 ? I know that supposedly my mass is increasing so it takes more energy but would I be aware of that? Would I think I double my speed from 2c/3 to 4c/3 (or really from my reference frame 0 to 2c/3 again?) while an onlooker sees me increase speed only slightly?

 

I am fairly new to this relativity concept and am trying to get my head around what different observers experience happen at high velocities.

[swansont]

But what if I try to double my speed at 2c/3 ? I know that supposedly my mass is increasing so it takes more energy but would I be aware of that? Would I think I double my speed from 2c/3 to 4c/3 (or really from my reference frame 0 to 2c/3 again?) while an onlooker sees me increase speed only slightly?

 

I am fairly new to this relativity concept and am trying to get my head around what different observers experience happen at high velocities.

 

The comparison of what you'd see and what somebody else sees is a change in the question. As long as you restrict yourself to two observers under inertial conditions, what you'd see would be symmetric, since either one of you could claim to be at rest. A third observer would see something different. But nobody would see you go faster than c under any conditions.

[Davros]

The start of the original post of this thread:

 

"If the fabric of space is expanding then the distances between galaxies is expanding, but this must also mean that the galaxies themselves are expanding."

 

Not correct. Imagine blowing up a balloon that has two spiders (galaxies) sitting on the surface. As the balloon enlarges the distance between the spiders grows but the spiders themselves do not change size.

[BigMoosie]

But their legs well get stretched apart?

[Davros]

expansion effects would be negligible for a galaxy compared to its own gravity.

[BigMoosie]

Ok, but it is there, I expected it to be practically null, but if everythink is expanding including star systems then so must the distance between the nucles and the electrons or perhaps even the size of subatomic particles.

[Davros]

Well I would actually think it is wrong to think of 'expansion' in a local area (eg within an atom or the solar system or even a galaxy).

 

There is a constant effect, rather than a constant expansion.

 

So if an object, or group of objects, is being held together by strong/weak forces or even weaker gravity, the expansion of space 'effect' merely reduces the effect of the above forces by an insignificant amount (maybe the orbit of pluto is a fraction of a mm further from the sun than might otherwise be the case.

 

The expansion 'effect' is constant, not increasing, within the the same locale. It only increases over distance.

 

(p.s. disclaimer: I do not have any formal science education, the above is my interpretation of my own reading).

[BigMoosie]

It does not matter how large the effects are, I wouldnt even go so far as a mm for pluto. But what I was getting at is that if we are perceiving that space is expanding then it is just as valid to say that time is speeding up (I know I said slowing in the title but I meant speeding). Can anybody see my argument?

[BlackDog]

Let me know if I worded that badly. In the meantime I have another question.

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. It would appear that they are both stationary; not spinning or moving. In that situation one on the planet would expect the moon to fall' date='[/color'] so would I, isn't everything relative?

 

still waiting for an answer to this question... anyone? i don't think that pendulam answer was correct. besides, what if the objects are not earth and moon, but two balls? hmm...

 

 

-shami

[Nicholas]

If space is expanding inbetween galaxies then space is stretching

or growing inbetween. This is not the same thing as these galaxies

moving through space away from each other.

 

There is a difference.

[Spyman]

still waiting for an answer to this question... anyone? i don't think that pendulam answer was correct. besides, what if the objects are not earth and moon, but two balls? hmm...

The pendulum answer by swansont is correct.

 

Some, threads You and BigMoosie may want to read:

 

Is rotation absolute or relative ? 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...