# Time dilation and gravity.



## Ray McCarthy (May 30, 2016)

We know a clock in orbit shows a different time to on the ground. The first test used atomic clocks on an aircraft.

Earth's core is younger than its crust
Earth's core may be years rather than days younger.



> Back in the early 1960s, physicist Richard Feynman remarked that the centre of the Earth had to be a little younger than the crust [ by a couple of days], since it would experience gravitational time dilation.
> ...
> a full calculation suggests it's two-and-a-half years.



Question everything and do actual sums and measurements.



> the paper says: “The pedagogical value of this discussion is to show students that any number or observation, no matter who brought it forward, must be critically examined” – especially since nobody had thought to question Feynman's remark until now.


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## Vertigo (May 30, 2016)

It's really rather a neat idea. Never considered it before


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## Ray McCarthy (May 30, 2016)

Hilarious quote from the HHGTTG?


			
				Blofield's Cat said:
			
		

> * So ... *
> *Dateline* 22 October 4004 BC, about 3:30 pm: *Place* the planet Magrathea:
> _Two figures stand on a construction gantry surrounded by partly assembled dinosaur skeletons and surplus firmament._
> "Right that's the crust finished, shall we call it a day?"
> ...


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## psikeyhackr (May 30, 2016)

So when are they going to do the calculations for Jupiter and the Sun?  LOL

psik


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## Vertigo (May 30, 2016)

They have done the sun (it's at the end of that article) and due to it's much greater variation in gravity it obviously has a bigger time difference - 39,000 years!


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## Stephen Palmer (May 31, 2016)

Blimey! never even thought of this before…


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## Ray McCarthy (May 31, 2016)

Nor had I in detail, though in hindsight since I knew about the aircraft test and also the guy that collects vintage atomic clocks ...
He took one THREE on holiday and up a US mountain in his big vehicle (with kids!) and saw the time difference.

This is the site I read.
Project GRE²AT: Photo Tour


> Perhaps you've heard: _A man with one clock knows what time it is. A man with two clocks is never sure_. But I would add further: _A man with three clocks is more sure than a man with two clocks_. And so the clock collection started...


LeapSecond Home Page

I have a clock set by radio code derived by atomic clock on 60KHz (very long Long Wave), a pair of standalone GPS receivers (they give atomic accurate time) and I have two crystal ovens, which are nothing like as stable as an Atomic clock, but about 1000x more accurate / stable than a "quartz" clock. A Metal back plastic case quartz crystal wrist watch never taken off is about 10x more stable than a quartz wall clock as your body heat gives a similar effect to a quartz oven. I also have a couple of modern Temperature Compensated Crystal Oscillators, (TCXO) which are 100th of cost of ovened crystal, a tiny fraction of power consumption and size and somewhere between an ordinary crystal oscillator (Quartz clock) and Ovened system.

I once built electronics to lock an electro mechanical pendulum clock (driving slave clocks throughout the building) all to a BBC Atomic synchronised source (which used Rubidium based clock).

People keep building better clocks, it reminds me some days of "The Thief of Time". They are down to a few seconds per life of universe or something crazy. They will be able to measure gravity more accurately! One has a microwave clock backup (Maser based) to the optical atomic clock so the optical one can be taken off line for maintenance.

There is a current ESA test satellite to measure gravity as well as a satellite mapping gravity on Earth


> ESA’s GOCE gravity satellite has already delivered [in 2012] the most accurate gravity map of Earth, but its orbit is now being lowered in order to obtain even better results.
> The Gravity field and steady-state Ocean Circulation Explorer (GOCE) has been orbiting Earth since March 2009, reaching its ambitious objective to map our planet’s gravity with unrivalled precision.
> Although the planned mission has been completed, the fuel consumption was much lower than anticipated because of the low solar activity over the last two years. This has enabled ESA to extend GOCE’s life, improving the quality of the gravity model.
> To be able to measure the strength of Earth’s gravity, the satellite was flying in an extraordinarily low orbit about 255 km high – about 500 km lower than most Earth observation satellites.


Second Mission
GOCE’s second mission improving gravity map

Earlier 2002 NASA / German mission
GRACE is a joint partnership between the NASA in the United States and Deutsche Forschungsanstalt fur Luft und Raumfahrt (DLR) in Germany. Project management and systems engineering activities are carried out by the Jet Propulsion Laboratory.
Missions - GRACE - NASA Science


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## Lew Rockwell Fan (May 31, 2016)

Ray McCarthy said:


> > _A man with one clock knows what time it is. A man with two clocks is never sure_.


I believe that chap's read his Kipling.


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## Nick B (May 31, 2016)

It would be interesting to calculate how much younger the centre of the galaxy is compared to Earth.


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## Vertigo (May 31, 2016)

Quellist said:


> It would be interesting to calculate how much younger the centre of the galaxy is compared to Earth.


Ooh now that would be interesting!

That also made me go look up our speed relative to the galactic centre (at around 20km/s rather less than I thought) where I also found that our orbit of the galaxy is not a simple one but oscillates above and below the galactic disk by some 250 light years. We are apparently currently in the midst of the disk, which is why it's so difficult to see our own galaxy, but in 14 million years time we'll be at the apex of our oscillation giving us a great view of our own galaxy. Learn something new every day...


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## Ray McCarthy (May 31, 2016)

Quellist said:


> how much younger the centre of the galaxy is compared to Earth


It may be in general much older as ours is second generation star. Hence we have heavy elements. The oldest stars are not going to have the heavier elements.

The age of our own solar system is estimated at about 4.6 Billion years*, our galaxy is about 13.6 Million years old.
This says the Earth is 4.3 billion years old
Age of the Earth - Wikipedia, the free encyclopedia

Due to size there is certainly  much more gravitational distortion of time than there is here.

Then how was life affected by the local supernova (or supernovae) that created the local bubble between 300,000 and 20 million years ago?
Local Bubble


> The very sparse, hot gas of the Local Bubble is the result of supernovae that exploded within the past ten to twenty million years


The Wiki editors also find info about the local bubble confusing
Talk:Local Bubble - Wikipedia, the free encyclopedia


10 Facts About the Milky Way - Universe Today.

Galactic Center - Wikipedia, the free encyclopedia

Perhaps the question is how old is the middle of area of the bar of the Galactic core compared to the Milky Way in general?

[* but what event is that estimated from?]


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## Ray McCarthy (May 31, 2016)

Vertigo said:


> That also made me go look up our speed relative to the galactic centre (at around 20km/s rather less than I thought)


Ah ... but Kepler's law mysteriously only seems to apply to planets and at ordinary interstellar distances, the fact that the further away you are, the slower the orbit.  Mysteriously at the galactic level every thing rotates at more like a record player disc*, though there is variation of rotation vs distance, it's nothing like as much as it ought to be. i.e the revolution time is the same or not much different as you move towards the edge. Hence also as galaxies are not moving apart at the speed the ought, "Dark Energy" and "Dark Matter" are postulated to make the equations "work" at the galactic scale. Observation does match theory at more "local distances" of planets and stars or even stellar neighbours.

[*Even a solid disc, the linear circular velocity is obviously increasing with distance from centre, but a different law compared to Kepler
Kepler's laws of planetary motion - Wikipedia, the free encyclopedia
vs
Tangential Speed - Wikipedia, the free encyclopedia
]


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## Vertigo (May 31, 2016)

Ah my figure was a little incorrect that was the figure for our speed relative to local rest, that is the average speed of all other stars in our 'local' vicinity. Our speed relative to the galactic centre is the speed we must travel to make one orbit of the galaxy, which takes approximately 225 million years, and that speed is about 220 km/s.

@Ray McCarthy I don't think we're talking about the relative age of stars here but rather the difference in age of all matter at the centre of the galaxy caused by relativity - ie time dilation. That difference will be caused by, I think, two things: the effects of time dilation caused by the gravity of the galaxy (much deeper in the gravity well at the centre) and by our relative motion (that being like the atomic clocks in orbit around Earth, but on a larger scale).


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## Ray McCarthy (May 31, 2016)

Vertigo said:


> I don't think we're talking about the relative age of stars here but rather the difference in age of all matter at the centre of the galaxy caused by relativity - ie time dilation.


Yes I know. But it's not simple.

Complicated by gravity, velocity and also when and where the things you are comparing were created. The Sun or Earth are single objects, so each has a narrow creation time. The Galaxy, our Earth and the bar of stars forming the galactic core are all disparate objects, so calculating what time dilation doesn't directly give a difference in age, that becomes a factor to whatever the relative age would be if time dilation didn't exist (due to gravity AND the differential speed)


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## Vertigo (May 31, 2016)

Well I certainly wouldn't want to try and calculate it and I wrote a program to calculate relativity time dilation...


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## Nick B (May 31, 2016)

I was thinking more along the lines of the galaxy as a single structure, with greatest mass at the centre, thinning to lowest mass at the edge. If you then drew a line from centre to edge with relative average (average because obviously mass depends on the amount of stars can vary dramatically) objective age of each 'ring'. 
You could work out, theoreticaly, where the oldest civilisations (from an sf perspective) may be.


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## Ray McCarthy (May 31, 2016)

Quellist said:


> I was thinking more along the lines of the galaxy as a single structure, with greatest mass at the centre, thinning to lowest mass at the edge.


I was sure you did think that, but I think two things:
1) It would only be a probability distribution.
2) Not all of the stars are same age.
3) Even apart from time dilation there isn't a simple prediction of age vs position
4) Some stars have been "captured" from other galaxies.
5) A civilisation might take between 1500 to 15000 years to get technological from first villages.
6) In the say 6 billion years of half the galaxy age of maybe an average planet, perhaps there could be +/- 1 Billion year variation on how fast a planet gets from slime to sentient, intelligent, language and tool using creatures at cusp of creating a civilisation. We only know our OWN timescale. So planet 1Billion years younger than us could have a civilisation 10,000 years more advanced than us. We can't know*. 

However perhaps you can work up some formula that sounds plausible for a particular SF story.

[* Though playing CIV II, III and IV on PC was fun, I had a lot of add on packs for Civ II. What if the creatures were more interested in research than war compared to us, less plague, or smarter or no giant dinosaurs etc ...]


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## J Riff (May 31, 2016)

Fantastic. I've ranted on about objects circling the entire galaxy, but mayhap it's just this arm of it, or.... sorry, too complicated. (Sits back to watch/listen to outer space science starting to make sense.)


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## Ray McCarthy (May 31, 2016)

Astronomy is nearly as good as chocolate or the other thing.


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## Lew Rockwell Fan (Jun 1, 2016)

/me scratches head and wonders about "the other thing".


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## Ray McCarthy (Jun 1, 2016)

And the mass of the Milky Way for your back of envelope gravity calculations is 700 billion times our own sun.
Which is 2,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 kg
(30 zeroes)

Milky Weigh: Galaxy in kg is...


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## Nick B (Jun 1, 2016)

Lew Rockwell Fan said:


> /me scratches head and wonders about "the other thing".



He meant astrophysics but forgot the word.


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## psikeyhackr (Jun 1, 2016)

Ray McCarthy said:


> And the mass of the Milky Way for your back of envelope gravity calculations is 700 billion times our own sun.
> Which is 2,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 kg
> (30 zeroes)
> 
> Milky Weigh: Galaxy in kg is...



Does that mean a Milky Weight bar will create a Black Hole in your stomach and suck you in?

psik


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## Ray McCarthy (Jun 1, 2016)

psikeyhackr said:


> Milky Way bar will create a Black Hole in your stomach and suck you in



Dunno. I used to prefer a Mars bar to a Milky Way. I worried about them and gave it up.


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## psikeyhackr (Jun 1, 2016)

Timing is everything!

Marcel Wolf – Google+

psik


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## Ursa major (Jun 1, 2016)

If there's a black hole at the centre of our galaxy, surely we can't know how much older the material at its "centre" (and so at the very centre of the galaxy) would be than, say, the material at the centre of our sun.


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## Ray McCarthy (Jun 1, 2016)

has time meaning beyond the event horizon of a black hole?


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## Vertigo (Jun 1, 2016)

I think we're forgetting where this thread came from; all the matter in the universe was created at the big bang - in that sense it is all the same age. However due to gravity time dilation some matter (in deep gravity wells) is 'older' that other matter. All that's being said here is that the centre of the sun is the bottom of a big enough gravity well that the centre is 39,000 years old than the outer layers and equally all the matter in the centre of the galaxy in at the bottom of an even bigger gravity well and so will have experienced even more time dilation and be even older relative to the matter at the outer edges of the galaxy. It's not about how old stars are but how much time the matter has experienced and due to relativistic effects that will vary. So we do know what the mass is at the centre of the galaxy and so can work out the different rates (is that the right word) of time at the centre and the outer edges.


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## J Riff (Jun 1, 2016)

Only an ET could not know what 'the other thing' is... drop the telepathic screen, Lew. )


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## Ray McCarthy (Jun 1, 2016)

Vertigo said:


> in that sense it is all the same age.


In another sense it not. The lighter elements are manufactured in the natural hydrogen fusion "factories" of the earliest stars created only from hydrogen.
Then the next stage is that dust and hydrogen form later stars.
Later in the history of the Universe or Galaxy, elements heavier than iron are formed. Above iron you have to put energy in. The radioactive elements around today are the youngest "matter".

List of radioactive isotopes by half-life - Wikipedia, the free encyclopedia
Start at bottom of page?
See 10^3 years and longer

Maybe more useful


> The following table lists ALL radioactive nuclei with a half-life greater than 1000 years. *An element decays away below detectable levels in about ten to fifteen half-lives.*


Radioactive isotope table
No naturally occurring Radioactive Elements found on Earth with less than 250 Million years half life, except traces of a few decay products.
Uranium-236 234,200,000 none
Uranium-235 703,800,000 rare
*15 half lives of 250 Million years is 3.75 Billion years
10 half lives of 700 Million years (Uranium 235) is 7 Billion years *

Thus my conclusion is that if the earth formed from accretion of dust, that dust is less than 7 billion years old and more than 3.75 Billion years old. Then as it became more packed the time is running slower for the core than the crust.

Similarly if the sun started as a loose hydrogen and collapsed due to gravity (eventually igniting Fusion due to pressure) the core time is running slower than the surface time. It all started as same age, but like one twin staying at home and the other on a space trip (the velocity of rocket causing the time dilation, more than gravity, which is inverse square law of diminishing to space) the traveller is younger. 

Some of the elements are being continuously created right now on Earth from heavier radioactive elements. Some of those heavier elements date from before the Solar system was formed, but were created long after the Big Bang in other stars.


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## Ray McCarthy (Jun 1, 2016)

J Riff said:


> Only an ET could not know what 'the other thing' is


Apparently it's a little older than the invention of wheat beer, I'd also think ET has it even if ET hasn't got beer.

I have theory that fermented drinks might be universal for ET, but only we have chocolate.


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## Vertigo (Jun 1, 2016)

Ah right we're in complete agreement re the time running slower bit, I was just being a little pedantic on the other. You see I'd argue that radioactive decay isn't really the creation of anything new just the manipulation of the existing particles - protons, neutrons et al. No new matter has actually been created therefore all matter in the universe is the same age except for that fiddly little relativity stuff. As I said, pedantic


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## Ray McCarthy (Jun 2, 2016)

Vertigo said:


> radioactive decay isn't really the creation of anything new just the manipulation of the existing particles - protons, neutrons et al


I suppose by same logic, then creation of of all elements above hydrogen is just the messing about with the the original protons etc.
I think I'd date objects from when the are identifiable as macro structure, which is younger than than when the elements created which is younger than the origin of the sub-atomic particles.

It doesn't matter, I think, as long as it's clear which of those three points of time you are considering.
We are made of stardust, simultaneously decades old, age of the most recent fusion reaction and age of universe?


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## Lew Rockwell Fan (Jun 2, 2016)

Vertigo said:


> I think we're forgetting where this thread came from; all the matter in the universe was created at the big bang - in that sense it is all the same age. However due to gravity time dilation some matter (in deep gravity wells) is 'older' that other matter. All that's being said here is that the centre of the sun is the bottom of a big enough gravity well that the centre is 39,000 years old than the outer layers and equally all the matter in the centre of the galaxy in at the bottom of an even bigger gravity well and so will have experienced even more time dilation and be even older relative to the matter at the outer edges of the galaxy. It's not about how old stars are but how much time the matter has experienced and due to relativistic effects that will vary. So we do know what the mass is at the centre of the galaxy and so can work out the different rates (is that the right word) of time at the centre and the outer edges.


?skrawkcab taht t'nsI


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## Nick B (Jun 2, 2016)

Vertigo said:


> I think we're forgetting where this thread came from; all the matter in the universe was created at the big bang - in that sense it is all the same age. However due to gravity time dilation some matter (in deep gravity wells) is 'older' that other matter. All that's being said here is that the centre of the sun is the bottom of a big enough gravity well that the centre is 39,000 years old than the outer layers and equally all the matter in the centre of the galaxy in at the bottom of an even bigger gravity well and so will have experienced even more time dilation and be even older relative to the matter at the outer edges of the galaxy. It's not about how old stars are but how much time the matter has experienced and due to relativistic effects that will vary. So we do know what the mass is at the centre of the galaxy and so can work out the different rates (is that the right word) of time at the centre and the outer edges.




All the matter in the 'observable' universe. It may not be all the matter in the universe.
Created at the same moment in time yes, but not traversing time at the same rate.


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## Lew Rockwell Fan (Jun 2, 2016)

Quellist said:


> All the matter in the 'observable' universe. It may not be all the matter in the universe.
> Created at the same moment in time yes, but not traversing time at the same rate.


No, I think he's right about that part. At least assuming the standard models are halfway correct, ALL matter, observable or not, including any that might lie beyond where we can ever observe it, even in principle, was created in the BB. If I'm wrong, please elaborate. I'm  pretty sure it IS backwards though. Time goes SLOWER in high g, not faster. So things deep in the hole are YOUNGER, not older. OP had it right.


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## Vertigo (Jun 2, 2016)

Lew Rockwell Fan said:


> No, I think he's right about that part. At least assuming the standard models are halfway correct, ALL matter, observable or not, including any that might lie beyond where we can ever observe it, even in principle, was created in the BB. If I'm wrong, please elaborate. I'm  pretty sure it IS backwards though. Time goes SLOWER in high g, not faster. So things deep in the hole are YOUNGER, not older. OP had it right.


Yes you're absolutely right - I'm not quite sure why I flipped it around and started talking about older instead of younger!  And yes I am obviously making the assumption that we've at least got that bit mostly right. Though there are these esoteric theories about matter constantly being created and destroyed in a vacuum - do they call it foaming or some such? And who knows what the lifetime of so called dark matter is...


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## Ray McCarthy (Jun 2, 2016)

Matter is likely created at the event horizon of a black hole.
Quantum foam. As long as average energy/mass in a vacuum is zero, then particles + antiparticles can arise for an "instant"*. If at event horizon then potentially one 1/2 of the mass "falls in" and other half "escapes".

For practical purposes though, perhaps the time the element under examination was created rather than age of big bang?

* See also Plank length and Plank Time. There isn't any known theoretical physics or quantum mechanics significance to these. However is there a minimum time interval or distance? Is time and distance granular?  This is all under consideration.


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## Nick B (Jun 2, 2016)

The observable universe refers to everything created at the big bang yes. That is why it is refered to as the observable universe. We cant measure anything that is outside that, either because it is so far away that the light from it hasn't reached us, or that there is nothing out there.
Theoretical models only deal with the observable universe, because anything else would be pure speculation. Generally, they don't say there isn't anything else out there though, because, again, that would also be pure speculation.


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## Mirannan (Jun 3, 2016)

Re. the time diffference between the galactic centre and Sol's neighbourhood:

Assuming new physics doesn't come into play (and it must, because at the centre of a black hole all the maths creates infinities, which doesn't make sense) the time elapsed at the very centre of the black hole at the centre of the galaxy is zero, at least since said BH formed. It's very unclear how long after the Big Bang the galactic black holes formed, but a reasonable figure to work with might be a billion years.

Take these two together, and one gets a time difference between the galactic centre and Sol of approximately 13 billion years.


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## mosaix (Jun 3, 2016)

I'm still not sure about the term 'old' here. Aren't we just saying that all the devices _that we use to measure time_ are affected by gravity? No surprise there.

I'm not sure that 'time' per se exists at all. I agree that we have devices that go tick-tock and vibrate etc. - so what? I agree that these devices, when subject to variations in gravity, tick-tock or vibrate at different rates. Does that make them 'younger' or 'older'. Maybe it does.


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## Nick B (Jun 3, 2016)

Time, at best guess (because the jury is still totaly lost on this one) is best discribed as a dimension, but a dimension we can only move in one direction within. Time, does of course, exist, and we experience it. If there was no time, we could have no meaningful experience.

To say time may not be real is the same as saying any other dimension we move in may not be real.  We do not understand it, but then our understanding of spatial dimensions may be just as flawed. But it exists, at the very least because it can be experiensed.


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## Ray McCarthy (Jun 3, 2016)

mosaix said:


> Aren't we just saying that all the devices _that we use to measure time_ are affected by gravity?


No. Less or more time "really" passes compared to an other observer  due to difference in gravity or velocity relative between the observer's location and the other observed location. Neither is wrong or correct, the exact opposite difference exists for an observer at the other location.

It's why the speed of light in a vacuum is constant, independent of the relative speed of observer or if it's a torch / laser shining in front and behind a space ship running at 0.3C. Both beams of light STILL are 1C, not 1.3C and 0.7C, which would be the case if there was no time distortion.

Thus light passing near a star (or esp a black hole)  vs more direct seems "bent", thus a heavy object acts as a giant lens made out of gravity rather than a different transparent medium.


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## Vertigo (Jun 3, 2016)

Mirannan said:


> Re. the time diffference between the galactic centre and Sol's neighbourhood:
> 
> Assuming new physics doesn't come into play (and it must, because at the centre of a black hole all the maths creates infinities, which doesn't make sense) the time elapsed at the very centre of the black hole at the centre of the galaxy is zero, at least since said BH formed. It's very unclear how long after the Big Bang the galactic black holes formed, but a reasonable figure to work with might be a billion years.
> 
> Take these two together, and one gets a time difference between the galactic centre and Sol of approximately 13 billion years.


Indeed although it's maybe more realistic or at least meaningful to look at the time difference between some point a good way outside the event horizon.



> I'm still not sure about the term 'old' here. Aren't we just saying that all the devices _that we use to measure time_ are affected by gravity? No surprise there.


@mosaix it is truly different ages. If I could get a spaceship that flew at a significant percentage of the speed of light and flew away from the Earth and back again for say ten years (measured on the spaceship). When I got back my physical body would have aged ten years but everyone on Earth would have aged considerably more than ten years; they are older than me. How much more depends on just how fast I managed to travel. This is not magic science or FTL this is known science (assuming I had enough energy available to achieve that high a speed). That's the familiar time dilation caused by relative speed but gravity time dilation is _exactly_ the same thing. As @Ray McCarthy has shown.


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## Ray McCarthy (Jun 3, 2016)

Vertigo said:


> This is not magic science or FTL this is known science


Proven too.


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## Mirannan (Jun 3, 2016)

Another way of explaining relativistic time dilation is that gravity (or acceleration, relativity also says that they are the same) distorts space-time in such a way as to reduce the amount of space and increase the amount of time - sloppily put, of course. Hence the length reduction of a moving object and the slowing down of time on same, as viewed by an observer not moving with the object.

Vertigo - A thought just occurred to me. Actually, the concept of duration inside a black hole (at least as viewed from outside) is meaningless because it is unobservable. However, it is possible to get arbitrarily small durations for a point outside the event horizon; the closer to said horizon, the shorter the duration as viewed from well outside. Actually at the event horizon, the duration is zero.


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## Ray McCarthy (Jun 3, 2016)

Mirannan said:


> the closer to said horizon, the shorter the duration


The "slower that time passes vs further away observer", is how I'd phrase it. But yes, past the Event Horizon, is like a ride on a photon, no time ever passes. The time passed for observer moving at speed of light compared to a fixed observer is always zero no matter the distance covered.


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## Lew Rockwell Fan (Jun 3, 2016)

Mirannan said:


> Re. the time diffference between the galactic centre and Sol's neighbourhood:
> 
> Assuming new physics doesn't come into play (and it must, because at the centre of a black hole all the maths creates infinities, which doesn't make sense) the time elapsed at the very centre of the black hole at the centre of the galaxy is zero, at least since said BH formed. It's very unclear how long after the Big Bang the galactic black holes formed, but a reasonable figure to work with might be a billion years.
> 
> Take these two together, and one gets a time difference between the galactic centre and Sol of approximately 13 billion years.


Are you sure 0 time is right for the CENTER? I'm ignorant, but I was under the impression that was correct for the event horizon, or more precisely, that as you approach the event horizon, dilation approaches infinity. I thought it was undefined inside the horizon.

============
Added by edit. Pardon, please. I should have read the whole thread before replying. I see you already said that in another post.


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## Lew Rockwell Fan (Jun 3, 2016)

Ray McCarthy said:


> Matter is likely created at the event horizon of a black hole.


Yes, I forgot about that. What I was trying to get at is that I was under the impression that the BB is thought to have created matter that is now beyond the limit of observability. In other words, in contrast to what's implied in:





Quellist said:


> The observable universe refers to everything created at the big bang yes.


Not my field, but are you sure of that? I was under the impression the BB is thought to have created ALL matter, and that  "observable universe" refers to that portion of it that Mr. Hubble isn't pushing away so fast it's red shifted beyond our ability to observe, even in principle.


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## SilentRoamer (Jun 3, 2016)

Lew Rockwell Fan said:


> Yes, I forgot about that. What I was trying to get at is that I was under the impression that the BB is thought to have created matter that is now beyond the limit of observability. In other words, in contrast to what's implied in:Not my field, but are you sure of that? I was under the impression the BB is thought to have created ALL matter, and that  "observable universe" refers to that portion of it that Mr. Hubble isn't pushing away so fast it's red shifted beyond our ability to observe, even in principle.



You're correct. The Hubble volume is the observable part of the Universe that appears in the visible spectrum. We can see "further" (although really you are talking about temporal distance as much as spatial) if you start talking about the CMBR, at some point this was all light. It's worth remembering though that the metric expansion of space derided from an exact solution of Einsteins field equations - basically space is expanding because it was always expanding since the early Universe inflationary periods.

As the expansion of space is an intrinsic metric of the Universe as a whole the Observable Universe will continue to become smaller. It is so easy to think of the Big Bang as an explosion of heat and matter in a pre-existing space but it wasn't an explosion in space it was the beggining of all space and everything that came to be in it everywhere. Personally I would expect the Universe to be spatially flat and infinite, it just makes more sense for there to be everything rather than just a bit of something. Although the Universe will die a heat death - lovely thought.


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## Ray McCarthy (Jun 3, 2016)

if the star has UV (mid band about 1 x 10^16 Hz)or maybe X-Ray, then the lower limit is maybe red-shift down to about 2GHz (2 x 10^9 Hz or about 10 million times lower). Problem is that the gain of a parabolic dish is related to square of diameter (that's simply the area of signal it intercepts), but the CUBE of the frequency. Thus a Radio telescope at 2GHz is *1000 times poorer* than at 20GHz if everything else is equal. Same size optical dish has MUCH more gain!
(I'm an RF Communications Engineer with experience in theory, design and practice of 0.05MHz to 22,000MHz gear, 2GHz = 2,000MHz)
Also the signal strength is inverse square law (1000 times distance is 1 millionth signal) as well as additional losses due to hydrogen and dust in space.

So the observable via radio Universe (seeing radio waves that started as UV light) has definite limits. It's easier though with radio to combine the signal from very many dishes to have effectively a larger dish. If the dishes are spaced out, it doesn't help the signal as such compared with the same number of dishes packed tight, but makes local noise easier to reject and improves the resolution as if it was a single larger dish, so an individual star in a distant galaxy can be picked out.

I am hoping to get a 3.7m mesh dish and I have receivers for 2.5GHz to 2.6GHz , 3.5GHz to 4.2GHz and 10.5GHz to 12.7GHz I can fit on it. The holes in mesh may be too large for more than 5GHz. It has elevation and azimuth actuators. I'd only be able to examine nearer stars though. Unlike an optical telescope, daytime is no limit. But rain, high ice crystals, snow  and the sun nearly inline would block the signal. Ordinary satellite TV is poorer for about 10 minutes for several days, twice a year as the Sun passes behind the TV satellite in spring and autumn.


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## Mirannan (Jun 4, 2016)

Lew Rockwell Fan said:


> Are you sure 0 time is right for the CENTER? I'm ignorant, but I was under the impression that was correct for the event horizon, or more precisely, that as you approach the event horizon, dilation approaches infinity. I thought it was undefined inside the horizon.
> 
> ============
> Added by edit. Pardon, please. I should have read the whole thread before replying. I see you already said that in another post.



I've been looking into this. Please note that I'm having to rely on experts; my physics is very rusty and was never this advanced in any case. The complicated answer is set out here:

What happens to spacetime inside a black hole? (Intermediate) - Curious About Astronomy? Ask an Astronomer

It can be summed up as saying that inside a black hole, time reverses in sign.

The simple answer is that, for anyone outside a black hole, the question of what happens inside it is meaningless (at least in scientific terms) because there is no possible way of observing it. Unless and until physics changes to include some form of FTL signalling, of course.


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