Over-complication of science

[hairykrishna]

Mr Whippy said:

The biggest thing for me has always been this red-shift/age of universe/where it's come from and going stuff. That light has been travelling millions of years, billions in the case of fringe galaxies. But then I get confused. That light has been travelling the age of the universe, so we are seeing the light of it when it was expanding rapidly after the 'big expansion'?
So it's no surprise that it was expanding a few billion years ago?

What is it doing now? Well we won't know that for billions of years I suppose. But they SAY as if it's a fact the universe is expanding. Considering we can't see red-shift within our galaxy it stands to reason that the universe might be collapsing very rapidly right now and we won't get a sign for millions of years until light from galaxies far enough away reaches us.

We're not just seeing light from ~14 billion years ago though, We're seeing all of the light from when the universe was a few hundred thousand years old, up to much more recently. Everything from the very old stuff to the most recent suggests that the universe is expanding. It would make no sense that the universe did that then suddenly and rapidly started collapsing in the past few million years. What would be the mechanism? Recent measurements in fact suggest that the expansion rate is increasing, rather than the opposite.

I think it's as close to a fact as you're likely to get. Assuming that stuff behaves as it has been doing when you've observed it, and that the laws of physics hold everywhere, has to be an assumption otherwise you get nowhere!

[Gene Vincent]

Mr Whippy said:

The biggest thing for me has always been this red-shift/age of universe/where it's come from and going stuff. That light has been travelling millions of years, billions in the case of fringe galaxies.(1)

But then I get confused. That light has been travelling the age of the universe, so we are seeing the light of it when it was expanding rapidly after the 'big expansion'?(2)

So it's no surprise that it was expanding a few billion years ago?(3)

What is it doing now?(4)

Well we won't know that for billions of years I suppose.(5)

But they SAY as if it's a fact the universe is expanding.(6)

Considering we can't see red-shift within our galaxy it stands to reason that the universe might be collapsing very rapidly right now and we won't get a sign for millions of years until light from galaxies far enough away reaches us.(7)

1/. There are no 'fringe galaxies' other than our visibility horizon, there is a huge amount of the Cosmos that is beyond our vision because light travels at a certain speed and the Inflation period was an expansion at much much faster than the speed of light.

2/. There was no starlight for the first 1.5milion years of this Cosmos, it was quite dark. The 'big expansion' you mention I presume you mean the inflationary period was totally dark, there is no light from that period for us to see.

3/. After that first 1.5 million years the Cosmos was still rather soupy, a rather chaotic mix of matter, Dark matter etc, there then followed a period where things coalesced, forming filaments of galaxies that look like a motorway does at night when viewed from an aeroplane, the dark spaces between these 'motorways' is full of Dark matter and Dark Energy.

4/. Exactly as it has done in the past, but the dark areas have over the last 14bn years grown into being of sufficient size individually for Dark energy to expand them by spontaneous (non-causal) production of empty space, any expansion in this Cosmos is not of anything you can see, the expansion gives off no light, but it does 'push' the matter that is visible around and that is the expansion we see, in short ... if you can see it, it ain't expanding, if you can't then it is and we know this because it's shoving the filaments around.

5/. See above.

6/. See above.

7/. See above.

[Mr Whippy]

1
Maybe I'm getting confused between frequency shift due to speed (does that actually happen with light?) or due to the space stretching?

Space stretching extends the wavelength so it goes red. But does travelling away in itself make things go red?

How do we even know the red shift is due to space stretching? Could another mechanism make it go red tinted? Perhaps deep space between galaxies has a scattering effect just like the sky, and the more deep space you look through makes it go red?!

When I said fringe, I mean fringe of observability.



2
The first 1.5 million years is a speck of time vs the length of the universe. If anything my question is more valid if the majority of expansion occurred during the dark period.
The fringe light we see right now set of billions of years ago. What we see is the universe near it's beginnings, not now. So how is observing the universe when it was young any indication of what it is doing today?


3
Yes, deep space is full of "dark matter" and "dark energy", two concepts used to account for observable phenomenon based on our current understanding.

4
Exactly has it has done in the past? All we have to go on is a tiny window of observations over 150 years. What we do get to observe is a fragment of time from between 100 million > billions of years ago.
Yes it stands to reason that it all must be expanding, but until you have a few frames of reference it's surely all an assumption that some other mechanism might not be at work?

How do you know dark matter in between galaxies has grown loads over the last 14billion years? Is that measured or assumed by some observation? What observation makes you conclude that it must have grown lots?

How is it shown dark matter expansion is pushing filaments around?


I'm happy to sit on the wall and be sceptical because these things tend to become partly wrong as understanding grows. I'm not going to buy into everything scientists say when they simply clamour to make models that fit observations until someone finds an observation that dis-proves it.

My observation is that if red shift mechanism is limited purely to deep space between galaxies, is it not just as likely that deep space filled with "dark matter" is actually just making the light tint red, or just changing the light frequency. Does it actually MEAN things are moving away faster the further away they are?
Have we observed things getting smaller over time to prove they are indeed getting further away?


I don't have the answers and don't know if I'm right or wrong but all these TV shows, and your answers, just leave oodles of questions left.


Is there any actual proof that red shift is due to galaxies physically moving away faster with increased distance at an accelerating rate?
What kind of speed is a galaxy 100,000,000 ly away moving at relative to us? At what speed is it accelerating? At what apparent rate should it's size be decreasing with time? Can we measure it? Is that even a valid check?

Are there alternative explanations that fit the observations using mechanisms that we don't know about yet? Bit of a weird question but I think it's valid.


I love science but sometimes scientists annoy me that they forget to convey their ideas without considering that they are just today's solutions to explaining our observations, which as always are limited themselves by our observational capabilities. Too often they are conveyed with a certainty which makes them fail to provide any kind of supporting material or reasoning, which is why it is so interesting to begin with!

Ie, Brian Cox just goes on for an hour about what is "going to happen", not explaining once how he has come to that observation, or the data to support it, all while using some analogy that requires travelling around the world when he could explain it stood in front of a black board!



Dave

[Mr Whippy]

hairykrishna said:

Mr Whippy said:

The biggest thing for me has always been this red-shift/age of universe/where it's come from and going stuff. That light has been travelling millions of years, billions in the case of fringe galaxies. But then I get confused. That light has been travelling the age of the universe, so we are seeing the light of it when it was expanding rapidly after the 'big expansion'?
So it's no surprise that it was expanding a few billion years ago?

What is it doing now? Well we won't know that for billions of years I suppose. But they SAY as if it's a fact the universe is expanding. Considering we can't see red-shift within our galaxy it stands to reason that the universe might be collapsing very rapidly right now and we won't get a sign for millions of years until light from galaxies far enough away reaches us.

We're not just seeing light from ~14 billion years ago though, We're seeing all of the light from when the universe was a few hundred thousand years old, up to much more recently. Everything from the very old stuff to the most recent suggests that the universe is expanding. It would make no sense that the universe did that then suddenly and rapidly started collapsing in the past few million years. What would be the mechanism? Recent measurements in fact suggest that the expansion rate is increasing, rather than the opposite.

I think it's as close to a fact as you're likely to get. Assuming that stuff behaves as it has been doing when you've observed it, and that the laws of physics hold everywhere, has to be an assumption otherwise you get nowhere!

My argument is that perhaps it's not expanding at all. We just think it is because of our single point observations.

Red shift is only something we observe between galaxies.

So dark matter as it's coined does something, it's either expanding space between galaxies, or it's just making the light go more red the more of it we look through?

Could that explain the same observations we make, or have we done other measurements to confirm expansion?

From what I read red shift was a general trend but using it to determine ranges wasn't really ideal at all.

Have we managed to plot a set of galaxies in space, and then check their positions years later and show they have moved apart by methods such as trigonometry as we move around in our own solar system and galaxy relative to others?


Or is it all just 'they are all red, smaller ones are more red, so they are further away and moving faster, so the universe is expanding at an increasing rate'



You could argue that because the sky is blue, and things further away are more blue, they are moving towards us at increasing speed the further away they are.

Maybe there is some movement, maybe there isn't. You can't tell until you do some more observations based on methods that are not tied to simply looking at the wavelength change.

Dave

[Gene Vincent]

Mr Whippy said:

1 Maybe I'm getting confused between frequency shift due to speed (does that actually happen with light?) or due to the space stretching?

Space stretching extends the wavelength so it goes red. But does travelling away in itself make things go red?

How do we even know the red shift is due to space stretching? Could another mechanism make it go red tinted? Perhaps deep space between galaxies has a scattering effect just like the sky, and the more deep space you look through makes it go red?!

When I said fringe, I mean fringe of observability.

2 The first 1.5 million years is a speck of time vs the length of the universe. If anything my question is more valid if the majority of expansion occurred during the dark period.
The fringe light we see right now set of billions of years ago. What we see is the universe near it's beginnings, not now. So how is observing the universe when it was young any indication of what it is doing today?

3 Yes, deep space is full of "dark matter" and "dark energy", two concepts used to account for observable phenomenon based on our current understanding.

4 Exactly has it has done in the past? All we have to go on is a tiny window of observations over 150 years. What we do get to observe is a fragment of time from between 100 million > billions of years ago.
Yes it stands to reason that it all must be expanding, but until you have a few frames of reference it's surely all an assumption that some other mechanism might not be at work?

How do you know dark matter in between galaxies has grown loads over the last 14billion years? Is that measured or assumed by some observation? What observation makes you conclude that it must have grown lots?

How is it shown dark matter expansion is pushing filaments around?


I'm happy to sit on the wall and be sceptical because these things tend to become partly wrong as understanding grows. I'm not going to buy into everything scientists say when they simply clamour to make models that fit observations until someone finds an observation that dis-proves it.

My observation is that if red shift mechanism is limited purely to deep space between galaxies, is it not just as likely that deep space filled with "dark matter" is actually just making the light tint red, or just changing the light frequency. Does it actually MEAN things are moving away faster the further away they are?
Have we observed things getting smaller over time to prove they are indeed getting further away?


I don't have the answers and don't know if I'm right or wrong but all these TV shows, and your answers, just leave oodles of questions left.


Is there any actual proof that red shift is due to galaxies physically moving away faster with increased distance at an accelerating rate?
What kind of speed is a galaxy 100,000,000 ly away moving at relative to us? At what speed is it accelerating? At what apparent rate should it's size be decreasing with time? Can we measure it? Is that even a valid check?

Are there alternative explanations that fit the observations using mechanisms that we don't know about yet? Bit of a weird question but I think it's valid.


I love science but sometimes scientists annoy me that they forget to convey their ideas without considering that they are just today's solutions to explaining our observations, which as always are limited themselves by our observational capabilities. Too often they are conveyed with a certainty which makes them fail to provide any kind of supporting material or reasoning, which is why it is so interesting to begin with!

Ie, Brian Cox just goes on for an hour about what is "going to happen", not explaining once how he has come to that observation, or the data to support it, all while using some analogy that requires travelling around the world when he could explain it stood in front of a black board!



Dave

1a/. Frequency shift is red-shift and the cause is Dark energy causing the dark areas of space to expand. There is an expected rate of redshift as things simply expand, but the expansion is not uniform, it has varying amounts of addition shift and what was for a while quite vexing for some was why, but it is really rather simple to explain the banding as simply shows the behaviour of the expansion is subject to gravitational forces and combined with specific expanses required for spontaneous production causes banding, immensely simple.

2a/. The Cosmos is quite uniform in behaviour, there is a smooth transition from 14bn years ago to today, nothing steps out of line without there being a reason and we strive to find exceptions as that either strengthens or modifies the standard Model.

3a/. DM and DE are part of GR, so are almost 100 years old, we have been struggling to make sense of it since then, we have a fairly good handle on them both now.

4a/. Don't let the short time of our observation confound your logic, just think of it as a window, a window in your house may only measure 900mm x 600mm but if you look through it, you can see for miles. So 150 years means nothing, the important number is the 14bn years.

You are conflating two distinct things as one or mixing them up, DM does not expand space, it taxes the expansion to perform subtle changes to the manner galaxies etc behave, or would behave if it were not there. DE causes the expansion acceleration.

Redshift is proof.

No, the entire point about DM is its lack of interaction, so it is not responsible for tinting the shift to red.

Our view is expanding at the speed of light. Year upon year.

Are there alternatives?

Of course there are, dozens if not hundreds, but they lack strength, they fall down at some point and the fall is irrecoverable without subverting almost everything we know works and has been observed.

Brian Cox does what he does because of the weight of investigation that preceded his pronouncements, same as my own pronouncements, they are based on tearing the heart out of hundreds of 'alternatives' and staying on course from all the back bearings we continually take.

[hairykrishna]

Mr Whippy said:

My argument is that perhaps it's not expanding at all. We just think it is because of our single point observations.

Red shift is only something we observe between galaxies.

So dark matter as it's coined does something, it's either expanding space between galaxies, or it's just making the light go more red the more of it we look through?

Could that explain the same observations we make, or have we done other measurements to confirm expansion?

From what I read red shift was a general trend but using it to determine ranges wasn't really ideal at all.

Have we managed to plot a set of galaxies in space, and then check their positions years later and show they have moved apart by methods such as trigonometry as we move around in our own solar system and galaxy relative to others?


Or is it all just 'they are all red, smaller ones are more red, so they are further away and moving faster, so the universe is expanding at an increasing rate'



You could argue that because the sky is blue, and things further away are more blue, they are moving towards us at increasing speed the further away they are.

Maybe there is some movement, maybe there isn't. You can't tell until you do some more observations based on methods that are not tied to simply looking at the wavelength change.

Dave

The number of things that would have to be in coincidence to trick us into believing the universe was expanding when it isn't is, at this point, enormous. There are also a number of clever independent observations along with redshift that makes us think the big bang, expanding universe model, is the right one.

Notably we have now more or less completely falsified the ‘tired light’ hypothesis. This is pretty close to your idea that there might be some stuff out there and the more of this stuff we look through, the redder stuff looks. A recent-ish test of this, vs the standard expanding theory, was looking at time dilation factors in supernova. Simply speaking, a supernova that will be observed to take twice as long as expected to decay when observed at redshift z=1. If it’s really not expanding out as fast as we think, regardless of how far away it is, then this factor won’t change depending on how far away (how redshifted) it is. So the Goldhaber and the Supernova Cosmology Project looked at a bunch of supernovas. Here’s the results;



Blue line is what we’d expect in an expanding universe. Red line is a ‘tired light’ model. Black is best fit.

Also weighing on the side of the expanding universe is the COBE (and other) observations of the cosmic microwave background. This matched incredibly closely what we’d expect in a big bang, expanding universe.

[Mr Whippy]

I'm confused with the supernova thing.

Utilising the red-shift to correlate against when it is the thing you want to call into question is a bit iffy.

Imagine we didn't know about the red shift all of a sudden, what other techniques might we use to determine the range of stars?

Assuming a galaxy is X intensity +/- a certain amount, then maybe we could range based on intensity? Ie, drop a galaxy within a range of potential distances?

Is there anything else apart from the red-shift that may indicate to us that galaxies/strings of galaxies are accelerating away from each other?



Is there anything like building a picture of a portion of space in 3D and then tracking those elements?

Over what time will the acceleration of expansion mean a doubling of the distances between galaxies?

Ie, is the angle between two distant galaxies increasing at an accelerating rate?


I'll be honest, I probably do think it's expanding, but it's frustrating to not see obvious answers to simple questions like those above covered anywhere, especially on those telly programs!
Good science programs need to challenge the ideas they present, that is scientific process and that is what makes it interesting and makes you understand the science.
Them just talking about what they think is right and not covering why they think that is just crap really

Say all the babble by all means, but give a rough explanation why you believe that to start with.

Dave

[Mr Whippy]

Gene Vincent said:

1a/. Frequency shift is red-shift and the cause is Dark energy causing the dark areas of space to expand. There is an expected rate of redshift as things simply expand, but the expansion is not uniform, it has varying amounts of addition shift and what was for a while quite vexing for some was why, but it is really rather simple to explain the banding as simply shows the behaviour of the expansion is subject to gravitational forces and combined with specific expanses required for spontaneous production causes banding, immensely simple.

I'm sorry but that is the most wooly worded explanation ever. It doesn't even sound like you understand or believe it.

Someone has done a massive correlation of point data for galaxies and their red shifts and said, near the gravitational effect of galaxies dark energy is more active in generating new 'space' between us and the observed points, that is why the red shift varied? So near the masses in space, the red shift isn't what we expect it to be?
Additional shift, as in more shifted to the red? And that is closer to the galaxies?

Is it not just as likely that red shift varies because things are different distances away?

What is the percentage error on ranging a galaxy purely with it's intensity/apparent size information vs red-shift ranging, do they correlate nicely?

Does these bands fall within the error range of ranging? What kind of distance variations do we see in these bands? How can we specifically associate them to banding generated due to the varying activity of dark energy in expanding space? Have other causes been considered and ignored? What are they?

If it's immensely simple then they should all be immensely simple answers. I genuinely am interested. I just think it's interesting to state WHY you believe that is the case, rather than just saying it.


I could just say "I think Jesus did it"... it's immensely simple.

No that wasn't very constructive was it? Thus it's nicer to read some responses with reasoning and explanation


Thanks

Dave

Edited by Mr Whippy on Thursday 1st November 16:51

[hairykrishna]

Mr Whippy said:

I'm confused with the supernova thing.

Utilising the red-shift to correlate against when it is the thing you want to call into question is a bit iffy.

Imagine we didn't know about the red shift all of a sudden, what other techniques might we use to determine the range of stars?

Assuming a galaxy is X intensity +/- a certain amount, then maybe we could range based on intensity? Ie, drop a galaxy within a range of potential distances?

Is there anything else apart from the red-shift that may indicate to us that galaxies/strings of galaxies are accelerating away from each other?


Is there anything like building a picture of a portion of space in 3D and then tracking those elements?

Over what time will the acceleration of expansion mean a doubling of the distances between galaxies?

Ie, is the angle between two distant galaxies increasing at an accelerating rate?

But the reason for red shift is what you're testing? i.e. if we're in an expanding universe the more red shifted, the more we'd expect the time dilation factor to increase. In a non-expanding universe this wouldn't be the case. I don't understand what the problem is? We know the light is red shifted, that's an observation. The test is to determine why.

To quickly answer some other questions (sorry, busy). Yes, we determine distance via luminosity too using objects we know the behavior of well. 'Standard Candles' is the term in astrophysics. Same with your 3d model- parallax.

Wiki does a pretty good job, actually - http://en.wikipedia.org/wiki/Cosmic_distance_ladde...

[Mr Whippy]

hairykrishna said:

If we're in an expanding universe the more red shifted, the more we'd expect the time dilation factor to increase. In a non-expanding universe this wouldn't be the case. I don't understand what the problem is? We know the light is red shifted, that's an observation. The test is to determine why.

Thanks for the linky, I'll take a look.

This is possibly where I'm getting confused.

Light always travels at the speed of light irrespective of the relative speeds?

So how can time dilation occur? If the light leaves X galaxy and arrives with us 20 million years later red shifted, isn't that purely due to the space through which the light travels having stretched... not that the light has had it's frequency slowed by the emitter travelling away at speed?

Ie, travel towards a green traffic light at 0.2c and it's still green? The light hitting our eyes is still travelling at c not 1.2c...?


If there is plenty of data to point towards an expanding universe without referencing red shift then I'm good with that. But if red shift data was the correlation base to which we check everything then I had a problem with that more than now

Dave

[Gene Vincent]

Mr. Whippy are you thinking along the lines of the 'tired light' hypothesis or Setterfields variable 'c' game of hide the pea?

[pointedstarman]

Gene Vincent said:

3a/. DM and DE are part of GR, so are almost 100 years old, we have been struggling to make sense of it since then, we have a fairly good handle on them both now.

I recently read an article by an Astrophysicist called Shirley Ho from Lawrence Berkeley Nation Lab who said "But for dark energy we are still pretty clueless." (April 2012)

Refreshingly honest I thought and she seems some way from having a fairly good handle on it. Have things move on that much since April?

[hairykrishna]

‘I

Mr Whippy said:

Thanks for the linky, I'll take a look.

This is possibly where I'm getting confused.

Light always travels at the speed of light irrespective of the relative speeds?

So how can time dilation occur? If the light leaves X galaxy and arrives with us 20 million years later red shifted, isn't that purely due to the space through which the light travels having stretched... not that the light has had it's frequency slowed by the emitter travelling away at speed?

Ie, travel towards a green traffic light at 0.2c and it's still green? The light hitting our eyes is still travelling at c not 1.2c...?


If there is plenty of data to point towards an expanding universe without referencing red shift then I'm good with that. But if red shift data was the correlation base to which we check everything then I had a problem with that more than now

Dave

Sorry I've explained it badly. Red light and blue light (and all other em radiation) travels at c. The red shift is a shift in frequency, not velocity, as I'm sure you know.

We know that there is red shift. Stars emit light with very distinct spectral lines - if these are at the wrong frequency then we know they've been shifted. We see a shift. Something is causing a frequency change in light emitted by distant galaxies.

The currently accepted, for want of a better phrase, argument is that these have been shifted because the space in between is expanding. If our relativity based models of the universe are correct, you can show that an important consequence is that to us here on earth time will also appear to run slower in distant galaxies. I say "you can show that" in the traditional physics hand waving explanation way, to mean "it's hard, it takes maths and you can find it in a reference" - appendix A of this paper is good; http://iopscience.iop.org/0004-637X/682/2/724/pdf/...


The time dilation is an independent test of expansion. If the Universe is expanding, then to an observer on Earth, time should appear to run more slowly in distant galaxies. To test it, you need a 'clock' to look at in a distant galaxy. Supernovas are perfect - their intensity follows a well known curve with a characteristic shape and duration.

So, in short... If the universe is expanding and our theories describe it well then the observed red shift should be accompanied by a time dilation observable in the light curves and follow a well defined model. It appears that it is. (see previous post or linked paper)

This leaves the rival theory in trouble. The counter argument was always that there could be something else causing the red shift; loss of energy by the photons over distance. This was already a bit shaky as we don't know of any mechanism that could do this, in the way that we observe. Now the mechanism also needs to explain the observed slower clock rate it looks increasingly improbable.

I hope that makes some sense...

[EliseNick]

hairykrishna said:

Sorry I've explained it badly.

[big snip]

I hope that makes some sense...

That's a great explanation - not something I know much about, so I feel I've learnt something today.

[Mr Whippy]

hairykrishna said:

‘I

Mr Whippy said:

Thanks for the linky, I'll take a look.

This is possibly where I'm getting confused.

Light always travels at the speed of light irrespective of the relative speeds?

So how can time dilation occur? If the light leaves X galaxy and arrives with us 20 million years later red shifted, isn't that purely due to the space through which the light travels having stretched... not that the light has had it's frequency slowed by the emitter travelling away at speed?

Ie, travel towards a green traffic light at 0.2c and it's still green? The light hitting our eyes is still travelling at c not 1.2c...?


If there is plenty of data to point towards an expanding universe without referencing red shift then I'm good with that. But if red shift data was the correlation base to which we check everything then I had a problem with that more than now

Dave

Sorry I've explained it badly. Red light and blue light (and all other em radiation) travels at c. The red shift is a shift in frequency, not velocity, as I'm sure you know.

We know that there is red shift. Stars emit light with very distinct spectral lines - if these are at the wrong frequency then we know they've been shifted. We see a shift. Something is causing a frequency change in light emitted by distant galaxies.

The currently accepted, for want of a better phrase, argument is that these have been shifted because the space in between is expanding. If our relativity based models of the universe are correct, you can show that an important consequence is that to us here on earth time will also appear to run slower in distant galaxies. I say "you can show that" in the traditional physics hand waving explanation way, to mean "it's hard, it takes maths and you can find it in a reference" - appendix A of this paper is good; http://iopscience.iop.org/0004-637X/682/2/724/pdf/...


The time dilation is an independent test of expansion. If the Universe is expanding, then to an observer on Earth, time should appear to run more slowly in distant galaxies. To test it, you need a 'clock' to look at in a distant galaxy. Supernovas are perfect - their intensity follows a well known curve with a characteristic shape and duration.

So, in short... If the universe is expanding and our theories describe it well then the observed red shift should be accompanied by a time dilation observable in the light curves and follow a well defined model. It appears that it is. (see previous post or linked paper)

This leaves the rival theory in trouble. The counter argument was always that there could be something else causing the red shift; loss of energy by the photons over distance. This was already a bit shaky as we don't know of any mechanism that could do this, in the way that we observe. Now the mechanism also needs to explain the observed slower clock rate it looks increasingly improbable.

I hope that makes some sense...

Yes it makes more sense now thank you!

The supernova element is also clearer... I've been doing a bit more reading again on time dilation.

The one thing that stumped me was saying bodies in accelerating states are those that suffer from time dilation effects (ie, why the astronaut who leaves earth and then returns has a slower clock), while earth clock stays faster.
But then the earth is also accelerating around the sun, and the sun around the galaxy, etc. Can any frame of reference really be isolated completely?

It all gets very messy in my brain. I'm sure it is all fairly correct but I do think there is something else to it all that might make it a bit clearer given more time and understanding.

I guess this is why unifying things, especially bringing the effects of gravity into things, is important.

Gravity is the bending of space time, and gravity dilates time? So maybe like supersonic aircraft in air, things moving fast in space time drag around the space time 3d grid and cause local dilations too?!


I'm just trying to make a picture that works in my head rather than just accept stated facts in isolation which can feel to make no sense.


Cheers

Dave

[Gene Vincent]

Mr Whippy said:

But then the earth is also accelerating around the sun, and the sun around the galaxy, etc. Can any frame of reference really be isolated completely?

The Earth isn't overall 'accelerating' around the Sun, overall it is marginally decelerating by about a second every 10 years.

But the important bit is the 'overall'... because our orbit is elliptical throughout the year the Earth accelerates and decelerates in its orbit around the Sun

So at this moment (4th Nov) we are accelerating to a peak orbital velocity at approx. the 1st/2nd Jan.

Edited by Gene Vincent on Sunday 4th November 18:28

[hairykrishna]

Mr Whippy said:

The one thing that stumped me was saying bodies in accelerating states are those that suffer from time dilation effects (ie, why the astronaut who leaves earth and then returns has a slower clock), while earth clock stays faster.
But then the earth is also accelerating around the sun, and the sun around the galaxy, etc. Can any frame of reference really be isolated completely?

It all gets very messy in my brain. I'm sure it is all fairly correct but I do think there is something else to it all that might make it a bit clearer given more time and understanding.

Yes, you're thinking about things to the extent you need to know a bit more relativity! The importance of the acceleration in the twins paradox is that it renders the two observers non-equivalent. There's no paradox because SR only states that all observers at rest in inertial reference frames are equivalent.

Essentially special relativity applies to inertial reference frames i.e. to coordinate systems that are not accelerating. So how does this work with earth? (and other stuff that's moving and has gravity!). We need a bit of general relativity, namely the equivalence principle. Leaving aside some complications, this in essence states that the force of gravity is equivalent to an acceleration of the reference frame. If you were in a spaceship, with no mechanism for looking outside, there is no experiment which you could perform which would be able to tell the difference between the spaceship out in deep space accelerating forwards at 9.8m/s and the spaceship sat in earths gravity.

This all leads to the additional interesting result that if the spaceship was in free fall, in a gravity well, this is exactly equivalent to it being motionless out in deep space somewhere with no gravity. Free fall is the same as no acceleration, which is an inertial frame, so special relativity applies. This means that, for the earth, there's no problem applying special relativity - being in orbit it's in free fall around the sun!

Of course it's not quite that simple, if your ref. frame is bound to the earth, in that you need to worry about the earths gravity and consider the results of GR at least along the 'vertical' axis.

Hopefully I've given you some idea how SR can still be applied in some frames which initially appear to be non-inertial though...

Sorry if this makes little sense or anything's wrong - I'm a little rusty on all this stuff.

[Mr Whippy]

Gene Vincent said:

Mr Whippy said:

But then the earth is also accelerating around the sun, and the sun around the galaxy, etc. Can any frame of reference really be isolated completely?

The Earth isn't overall 'accelerating' around the Sun, overall it is marginally decelerating by about a second every 10 years.

But the important bit is the 'overall'... because our orbit is elliptical throughout the year the Earth accelerates and decelerates in its orbit around the Sun

So at this moment (4th Nov) we are accelerating to a peak orbital velocity at approx. the 1st/2nd Jan.

Edited by Gene Vincent on Sunday 4th November 18:28

Isn't it accelerating as it perpetually 'falls' towards the sun, or is it best to see that not as acceleration but as following the curvature of space?

I thought they should be one and the same thing?

hairykrishna said:

Mr Whippy said:

The one thing that stumped me was saying bodies in accelerating states are those that suffer from time dilation effects (ie, why the astronaut who leaves earth and then returns has a slower clock), while earth clock stays faster.
But then the earth is also accelerating around the sun, and the sun around the galaxy, etc. Can any frame of reference really be isolated completely?

It all gets very messy in my brain. I'm sure it is all fairly correct but I do think there is something else to it all that might make it a bit clearer given more time and understanding.

Yes, you're thinking about things to the extent you need to know a bit more relativity! The importance of the acceleration in the twins paradox is that it renders the two observers non-equivalent. There's no paradox because SR only states that all observers at rest in inertial reference frames are equivalent.

Essentially special relativity applies to inertial reference frames i.e. to coordinate systems that are not accelerating. So how does this work with earth? (and other stuff that's moving and has gravity!). We need a bit of general relativity, namely the equivalence principle. Leaving aside some complications, this in essence states that the force of gravity is equivalent to an acceleration of the reference frame. If you were in a spaceship, with no mechanism for looking outside, there is no experiment which you could perform which would be able to tell the difference between the spaceship out in deep space accelerating forwards at 9.8m/s and the spaceship sat in earths gravity.

This all leads to the additional interesting result that if the spaceship was in free fall, in a gravity well, this is exactly equivalent to it being motionless out in deep space somewhere with no gravity. Free fall is the same as no acceleration, which is an inertial frame, so special relativity applies. This means that, for the earth, there's no problem applying special relativity - being in orbit it's in free fall around the sun!

Of course it's not quite that simple, if your ref. frame is bound to the earth, in that you need to worry about the earths gravity and consider the results of GR at least along the 'vertical' axis.

Hopefully I've given you some idea how SR can still be applied in some frames which initially appear to be non-inertial though...

Sorry if this makes little sense or anything's wrong - I'm a little rusty on all this stuff.

I think I just need to re-read the materials I have many times so it begins to sink in.

The argument I made for myself was that if I left the earth counter to the earths orbit (where it'd been) I'd be accelerating from the earth's inertial plane of acceleration into the same inertial plane as the suns. I'd then succumb to it's gravity and accelerate towards the sun.
To stop that falling into the sun, I'd need to 'accelerate' away from it at some rate.
So I'm now kinda following the sun around in the galaxy arm so I'm in a consistent inertial frame of reference with the local clump of stars, but accelerating away from the earth and away from the sun?

Surely the universe is so twisted in time that it's hard to say how old anything is? If actual speed in space is cumulative and it's really expanding so quickly then good chunks of it might be moving at near to the speed of light all the time, even us? So we might be ageing very slowly vs some more static observer? But static to what I guess? What if 'universal' static is moving away from Earth at 0.5c towards Polaris?
I guess you could argue it never matters because by the time you 'realise' the difference in time by accelerating back to somewhere for it to matter then you have balanced it out to make sense by that time, or to observe the difference then it makes sense by the time the message gets to you at speed c.

Hmmmmm


Ie, watching a supernova from earth we might be moving towards or away from it at massive speeds, and the same for the supernova. Of course we can look at our clock and say it's consistent for our observations, but if these supernovae might be accelerating towards or away from us at massive speeds within galaxies then surely that causes a problem?

If the speed of expansion is enough to offset the movement of a supernova within a galaxys arm towards us, then the rate of expansion must be massive. Which then makes me wonder why all these galaxies we can see are not moving apart from each other when we look up into the sky?!

Hmmmm

Dave

[Gene Vincent]

Mr Whippy said:

Isn't it accelerating as it perpetually 'falls' towards the sun, or is it best to see that not as acceleration but as following the curvature of space?

I thought they should be one and the same thing?

No.

It is a gravitational lock.

If, for example, our Sun were to instantly convert itself into a Black Hole Star, our orbit would not change one iota despite circling what is, in many peoples minds, a 'death star'...

[Mr Whippy]

But the stars gravitation would be replaced by the black holes, so why would it change?

If you remove the sun wouldn't our path suddenly be a straight one relative to where the sun once was?

I thought just as a geostationary satellite is perpetually falling towards earth (and so accelerating as it is changing direction all the time), the same is said of earth falling towards the sun?

Isn't that the definition of acceleration? Changing velocity, and the velocity vector is changing all the time?


Or can we treat gravitational acceleration differently to centrifugal when dealing with items following the space time bendiness?

Hmmm

Dave