Relativity and Cosmology Blog

Relativity and Cosmology

This is a Blog on relativity and cosmology for engineers and the like. My website "Relativity-4-Engineers" has more in-depth stuff.

Comments/questions of a general nature should preferably be posted to the FAQ section of this Blog (http://cr4.globalspec.com/blogentry/316/Relativity-Cosmology-FAQ).

A complete index to the Relativity and Cosmology Blog can be viewed here: http://cr4.globalspec.com/blog/browse/22/Relativity-and-Cosmology"

Regards, Jorrie

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Relativity/Cosmology FAQ

Posted September 26, 2006 2:56 AM by Jorrie
Pathfinder Tags: cosmology FAQ relativity

The same (or similar) questions on this topic tend to come up from time to time. Rather than scatter answers all over this forum, I will try to collect them here, in one continuously updated post. You are welcome to reply with questions or comments. Please stick to questions or comments on standard, mainstream relativity or cosmology - this is not the place for voicing disagreements with mainstream science! If you want to do that, start a new thread.

The first one (actually a batch!) is from Erich:

Q1: "Where is point zero in the universe? At what velocity are we relative to point zero? In which direction do we accelerate to increase our velocity? How close are we to the speed of light? Is this theoretically even possible to calculate? Maybe the speed of light is not that far away relative to point zero?"

A1: It is not clear what is meant by "point zero", but the closest thing I can think of is a point at rest w.r.t. the cosmic microwave background (CMB) radiation. Our part of the universe (our local group of galaxies) moves at about 600 km/s or about 0.002c relative to the CMB. This velocity seems constant - if we are accelerating, it is too small to be detected at present.

If however, "point zero" meant "center of the Big Bang (BB)" or "center of the cosmos", the answer is simple: there is no such thing as a point that represents the BB or the center of the cosmos. The BB happened everywhere at once.

Q2: If there is no absolute reference in the universe, how can there be a speed limit?

A2: The 'speed limit' refers to relative speed. Einstein predicted and experiment confirmed that however hard we try, we will not succeed in 'boosting' anything to even reach the speed of light relative to us, never mind exceeding it. For this to be true, we must be at rest in one inertial frame of reference, or course.

Q3: How do we know that the Cosmic Microwave Background (CMB) does not define an absolute frame of reference, the only one in which light propagates at "c"?

A3: As Earth orbits the Sun at 30 km/s, our velocity relative to a given spot in the CMB, lying near the ecliptic, changes periodically with a peak-to-peak value of 60 km/s. We can measure this velocity change by means of the redshift change of the CMB.

We are however unable to detect a change in the speed of any light coming from that general direction, e.g., from pulsars. This indicates beyond reasonable doubt that the measured speed of light is independent of our movement relative to the CMB.

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#1

Re: Relativity/Cosmology FAQ

09/26/2006 4:12 AM

It might be worth adding that if by "point zero" he means "centre of the universe" - there is no centre.

Unless I'm out of date and thinking has changed, our 3-dimensional universe is embedded in 4-dimensional hyperspace. It's analogous to 2-dimensional beings inhabiting the surface of a 3-dimensional sphere (which they have no way of visualising or detecting). So there are no centre or boundaries, all points are equivalent, and if you keep going in one direction you come back to your starting point. Also in an expanding universe (equivalent to the sphere expanding in the 2/3-dimensional case) every point recedes from every other and there is no centre of expansion. Rate of recession is proportional to distance apart, in agreement with Hubble's Law.

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#2
In reply to #1

Re: Relativity/Cosmology FAQ

09/26/2006 12:10 PM

I agree CodeMaster, thanks, will add it to the FAQ.

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#3
In reply to #1

Re: Relativity/Cosmology FAQ

09/26/2006 2:37 PM

I think we are free to choose a "zero point" or origin, depending upon what we are interested in. For instance we can choose the center of our galaxy as an origin that is stationary and measure the relative speed of our solar system as we rotate about the center of the galaxy. On smaller scales, choice of an origin is obvious, the sun, the center of the milky way, but on a larger scale, I don't think there is a point that we can choose as an obvious origin.

By "obvious origin" I mean to say that the choice of origin greatly simplifies the equations of motion involved. Is there such a thing for the very large scale? If the furthest galaxies are 14 Billion lightyears away, does that mean that 7 billion lightyears away is close to an origin. I don't think that's the case, but I'm not 100% sure why.

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#5
In reply to #3

Re: Relativity/Cosmology FAQ

09/27/2006 5:45 AM

Quoting Roger: 'By "obvious origin" I mean to say that the choice of origin greatly simplifies the equations of motion involved. Is there such a thing for the very large scale? If the furthest galaxies are 14 Billion lightyears away, does that mean that 7 billion lightyears away is close to an origin. I don't think that's the case, but I'm not 100% sure why.'

Correct on the first count - choose the origin of your coordinate system so as to simplify the equations. As for the question, there is no such 'origin' halfway to the edge. In a presumably infinite, homogeneous and isotropic (on large scales) cosmos, all points are equal. On small scales, there are always things like clusters, galaxies, solar systems, as you said, that may be convenient as origins.

Wherever we are, we're at the exact center of our observable cosmos. So why not choose ourselves as the origin? For some applications, that may be the best, for other's it may surely not be.

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#7
In reply to #5

Re: Relativity/Cosmology FAQ

09/27/2006 1:00 PM

"Wherever we are, we're at the exact center of our observable cosmos."

Its hard for me to get my head around this. Is it true that if we look in any direction we can see galaxies that are 13 billion years old, or is it only a certain section of the night sky that we can see them? I know inflation makes the Cosmic Background Radiation show up in all directions, but galaxies formed after there was some inflation, so I don't see why it should be in all directions. It seems like there should be a preferred direction, I'm not sure. Can you offer any insight?

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#8
In reply to #7

Re: Relativity/Cosmology FAQ

09/27/2006 1:54 PM

Quoting Roger: "Its hard for me to get my head around this. Is it true that if we look in any direction we can see galaxies that are 13 billion years old, or is it only a certain section of the night sky that we can see them?"

It is indeed a hard thing to get one's head to accept! I we disregard the plane of the Milky Way, which masks all distant objects, yes, we can observe galaxies to almost (but not quite) 13 billion years of light travel time in all directions.

To make it more palatable, think of an infinite universe that is isotropic and homogeneous on the large scale. Wherever we are, it must look the same in all directions. There is no edge, just a horizon over which we cannot observe, because light did not have time to reach us from more distant areas. We think this is so because we also have evidence that the universe has a finite age.

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#4

Re: Relativity/Cosmology FAQ

09/27/2006 4:46 AM

I have basicly the same question az Erich, but maybe the phrazing will help us understand.

If there iz no absolute reference, how can there be a speed limit?

Get your space ship up to 50% uv lite speed & its taking more energy to add each further increment uv speed, so just reset the speedometer to zero!

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#6
In reply to #4

Re: Relativity/Cosmology FAQ

09/27/2006 7:41 AM

Z man, you wrote: "If there is no absolute reference, how can there be a speed limit?"

The 'speed limit' refers to relative speed. Einstein predicted and experiment confirmed that however hard you try, you will not succeed in 'boosting' anything to even reach the speed of light relative to you, never mind exceed it. For this to be true, 'you' here refers to an inertial reference frame with you at rest in it.

You further said: "Get your space ship up to 50% of light speed & its taking more energy to add each further increment of speed, so just reset the speedometer to zero!"

Remember that the speed that appears in the energy equation is the speed relative to your original inertial reference frame. If your ship was accelerated to now cruise at 0.5c relative to the original reference frame, how would you reset the speedometer? Just 'tweaking the knob' does not change the real relative speed or the energy equation!

If this does not make sense to you, take a look at my website for some basics on relativity.

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#10
In reply to #6

Re: Relativity/Cosmology FAQ

09/27/2006 6:20 PM

This is getting more and more interesting! I will add some more; Have you thought of this? questions later. I found something interesting which may be food for thought? possibly relevant to this discussion. Click onto the website as mentioned previously, "website for some basics on relativity."

Next Relativity 4 Engineers Weblog

Next Satellite reveals universe's first trillionth second. JOHNS HOPKINS UNIVERSITY NEWS RELEASE Posted: March 16, 2006

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#12
In reply to #10

Re: Relativity/Cosmology FAQ

09/28/2006 12:33 AM

Erich, you must be careful reading the popular articles too literally. I think you refer to the opening statement of the article: "Scientists peering back to the oldest light in the universe have new evidence for what happened within its first trillionth of a second, when the universe suddenly grew from submicroscopic to astronomical size in far less than a wink of the eye."

In technical articles/books, this is phrased slightly differently, like "…., when the spacing of particles in the universe suddenly grew from submicroscopic to astronomical size in far less than a wink of the eye." Sometime also as: "… when our observable universe suddenly grew from submicroscopic to astronomical size in far less than a wink of the eye."

The reason is that it is very likely that the total universe is infinite and started out as infinitely large. Our observable universe is however finite and could have started as a subatomic portion of the whole. This does still not mean that there is a single point of origin that we can detect today. The whole observable cosmos was that 'zero point'!

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#13
In reply to #12

Re: Relativity/Cosmology FAQ

09/29/2006 1:41 AM

In the popular article, as well as the 2 technical articles, the word grew is mentioned. The article mentioned here, even has a misleading drawing, in an attempt to convey their concept. The question then is: Where did the particles come from, how did they get there, and how is it possible for submicroscopic particles to expand to that extent. It seems that particles appeared throughout infinity; and they grew. Our observable universe may seem finite to us in the same way that Columbus viewed the earth. [Man's point of origin is the earth, which is a particle in our universe]. I also agree with your last sentence, but, where where did the particles come from?

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#14
In reply to #13

Re: Relativity/Cosmology FAQ

09/29/2006 2:21 AM

Erich, you wrote: "It seems that particles appeared throughout infinity; and they grew… …I also agree with your last sentence, but, where where did the particles come from?"

The particles did not grow, AFAIK. As I understand the inflationary scenario, it was pure vacuum energy and radiation during the inflation epoch. Loosely speaking, the particles were created by the excess energy when inflation stopped and normal decelerating expansion took over. From then on, the distance between the particles grew, not the particles themselves.

My page on inflation describes it a bit better, but still from an engineer's point of view

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#16
In reply to #14

Re: Relativity/Cosmology FAQ

09/29/2006 1:02 PM

This is absolutely amazing!! I'm used to inventing within our environment, and it appears that I have not even scratched the surface, which is very humbling, and inspiring to me.

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#43
In reply to #6

Re: Relativity/Cosmology FAQ

08/27/2008 4:17 PM

Oh this is terrible. I've just discovered your website. How far does the landscape of information go? I feel like I've stepped on to an infinite plain and I'm too obsessed to step off.

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#9

Re: Relativity/Cosmology FAQ

09/27/2006 4:48 PM

WARNING: Tongue-in-cheek humor attempt......

I am reminded by the above discussion of a (now) famous quote from the 1984 film, "The Adventures of Buckaroo Banzai Across the 8th Dimension":

"Remember; no matter where you go, there you are." Buckaroo Banzai

(8th Dimension? Hey, I thought you guys said there are only 4 dimensions!)

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#11
In reply to #9

Re: Relativity/Cosmology FAQ

09/27/2006 6:41 PM

I hate to be a "GRINCH" with no humor! I think this a very important, and serious discussion.

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#15

Re: Relativity/Cosmology FAQ

09/29/2006 2:45 AM

!WARNING! There are monkey boyz in the facility.

I've read some of it. I also read Einstienz book for laymen many yearz ago. The way I'm thinking now, it seemz that space/time must hav a kind uv structure, like a fabric, or particlez.

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#17
In reply to #15

Re: Relativity/Cosmology FAQ

09/29/2006 1:32 PM

Quoting: "I've read some of it. I also read Einstiens book for laymen many years ago. The way I'm thinking now, it seems that space/time must hav a kind uv structure, like a fabric, or particles." (sic.)

Yep, you remember correctly, more or less. Spacetime can be thought of as a 'fabric', out of which virtual particles may pop up and disappear quickly again - according to quantum physics.

In straight Einsteinian relativity, there are no particles associated with spacetime - it's just like a fabric that can be deformed, stretched or compressed. On the 'surface of this fabric', particles can move, but they are not part of the 'fabric'. What's more, this fabric is not absolute - it's relative. You simply cannot measure your speed relative to this fabric - weird!

You must take into account that both the above are just 'toy theories', i.e., the simplest theory that can explain observations. Neither of them claims any fundamental truth, whatever that may mean (as Stephen Hawking likes to say).

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#18

Re: Relativity/Cosmology FAQ

09/30/2006 12:40 AM

Weird iz rite.

So, woud this conversation make sense?:

"Scotty! We got up to 200,000,000 KpH with only 10 gallonz uv dilithium crystalz. So why hav we used up 5 more gallonz to get to 220,000,000? Did you break a float hinge in the carburator or wut?"

"No Captian Kirk. Its your fault! You forgot to change your perspective to an inertial frame thats headed in the direction we are going!"

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#19
In reply to #18

Re: Relativity/Cosmology FAQ

09/30/2006 12:53 PM

Good question Z man. I was going to ask that one next. Is there a way in which NASA can verify; maybe just launch rockets from opposite sides of the globe at the same time, and see if there is any difference. This may take 6-12 rockets into outer space precision timed and launched from different opposite locations 45 degrees apart. [How to do this is another subject.] Am I out to lunch? Can we go with the flow or a head-on direction. Could this establish the direction of the flow of our place in the universe. If you come back down to earth, and take note of a river or ocean currents flowing with billions of plankton flowing with the current. They all flow relative to each other. It would be easy for them to move faster straight ahead and also take no effort to move up to 90 degrees left or right. Now going against the current is more difficult. Can one measure this in oouter space? Have experiments been done to verify anything?

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#20
In reply to #19

Re: Relativity/Cosmology FAQ

09/30/2006 1:00 PM

90 degrees in any direction from point straight ahead and any angle in between. Sorry I missed that before.

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#21
In reply to #20

Re: Relativity/Cosmology FAQ

09/30/2006 2:18 PM

Hi Zman and Erich. What you are speculating on means stepping 101 years back into history, to before Einstein abolished absolute space and absolute time. You can launch things in any direction from Earth you choose. They may have different velocities relative to the Sun, but try as you might, you will not be able to establish movement relative to the 'fabric' of spacetime. If this was not so, GPS would not work!

About "No Captian Kirk. It's your fault! You forgot to change your perspective to an inertial frame that's headed in the direction we are going!"

True, the calculated kinetic energy depends absolutely on which frame of reference you calculate it relative to. What is also true is that if you keep the reference frame inertial, i.e. unaccelerated, the amount of energy required to accelerate an object relative to that frame increases as per Einstein's special relativity, i.e.,

E = Mc2/sqrt[1-(v/c)2], where M is rest mass of an object, v velocity relative to the reference frame and c the speed of light. This equation is routinely verified in linear particle accelerators.

Using this, Captain Kirk can choose any inertial frame he fancies and have fun calculating the amount of fuel required to accelerate from rest in that frame to any velocity (less than c) relative to it!

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#23
In reply to #21

Re: Relativity/Cosmology FAQ

09/30/2006 4:25 PM

I thought it would be a long shot! Thank You Jorrie, for your explanation.

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#22
In reply to #20

Re: Relativity/Cosmology FAQ

09/30/2006 4:10 PM

I hate to get of the topic, but let's go back to #3 Roger Pink & #5 Jorrie for just one moment. I see a flag waving waving every time I read #3 & #5.

Roger Pink: Your last paragraph #3 " By "obvious origin" I mean to say that the choice of origin greatly simplifies the equations of motions involved."

Jorrie; Your last pragraph in #5 "Wherever we are, we're at the exact center of our observable cosmos. So why not choose ourselves as the origin? For some applications, that may be the best, for other's it may surely not be".

Why don't we simplify the equations of motion involved? Is it possible to verify which applications may be best, and verify others which may surely not be, if there are any? The scale may tip in the direction of change! Simplicity can open new doors of understanding and knowledge. This may be a positive move in the right direction?

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#24
In reply to #22

Re: Relativity/Cosmology FAQ

10/01/2006 6:01 AM

Erich, you wrote: "Why don't we simplify the equations of motion involved?"

It is normally reasonably easy to know which origin of the coordinate system is best, i.e., giving the simplest equations. Apart from the more mundane coordinates we use on Earth's surface, for orbital work it is usually geocentric coordinates, centered on Earth's center of mass. For solar system work, it is usually heliocentric and for larger scale it is usually galactocentric, meaning centered on the Milky Way's center of mass.

When working with the cosmos as a whole, it is actually simplest to choose a reference frame that is at rest relative to the CMB, with us momentarily at the origin. Cosmologists call this 'co-moving coordinates'. Everything in the cosmos, us included, is likely to be moving relative to CMB, so one cannot point to a physical object and say "that's it, the origin of the absolute coordinate system". In short, there is no absolute coordinate system that we can detect.

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#25
In reply to #24

Re: Relativity/Cosmology FAQ

10/01/2006 10:54 AM

Very Good! Thank You! I have to get back to my down to earth inventions, which I will share with you in the future, under Mechanical Engineering. Your patience and your time was much appreciated. I will continue to read Jorrie's Blog. Erich

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#26

Re: Relativity/Cosmology FAQ

04/23/2007 12:27 PM

Hi Jorrie, a general cosmology question: if the universe started out as a point-singularity, how can it be almost(?) infinite today? I'm referring to the 'flat' universe, which goes on forever.

SL

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#28
In reply to #26

Re: Relativity/Cosmology FAQ

04/23/2007 1:33 PM

Hi SL, this is an almost(?) impossible question to answer.

You must take into account that the most useful model that we have today is the ΛCDM (Lambda-cold-dark matter) model, based on the Friedmann equation, where Lambda means Einstein's cosmological constant (the energy of the vacuum).

This model fully complies with Einstein's field equations (general relativity), but it is still just a model. Only one thing is certain: the ΛCDM model is incomplete and will be updated as more information becomes available.

Anyway, according to this model, if the universe is flat or open (Ω ≥ 1), the singularity was actually infinite in size! The term 'singularity' here refers to infinite density, not zero size. In fact, since Einstein's theory can only be applied to sizes above the Planck length (~10-35m), it tells us that the singularity consisted of an infinite number of Planck volumes, each containing some energy - i.e., infinite total energy...

You spot the problem?

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#27

Re: Relativity/Cosmology FAQ

04/23/2007 1:07 PM

Hi Jorrie, sorry for the many questions, but since you invited this in your Blog header, here's another one that is bothering me.

It is said that we can observe only as far as light has had time to travel since the B/Bang. So will we be able to observe farther and "more" as time goes on? I mean, in another billion years, would our descendants (if any) be able to observe to 15 billion light-years and measure more distant quasars?

SL

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#29
In reply to #27

Re: Relativity/Cosmology FAQ

04/23/2007 1:53 PM

Hi SL, you wrote: "sorry for the many questions, but since you invited this in your Blog header, here's another one that is bothering me."

Boy, am I starting to regret that invitation!

In fact, this one is far easier to answer than your previous one.

While the old "Einstein-de-Sitter" model (just enough mass-energy to balance the expansion rate) was the preferred one, our descendants would have observed more and more of the universe. The reason is that the expansion rate was slowing down, or so it was thought.

Since the ΛCDM model (explained in my previous reply) with its increasing expansion rate fell into favour (backed by a lot over cross-correlating observational evidence), the sad thing is that our descendants may observe less and less...

The pesky Λ (vacuum energy, that nobody understands) is the root cause of this undesirable state of affairs. The CDM tries its best to correct the issue, but it looks like Λ wins...

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#30

Re: Relativity/Cosmology FAQ

03/22/2008 4:07 PM

Hi Jorrie,

If the big bang happened everywhere at once, and the CMB is the leftover of it, then how is it possible to measure our speed with respect to the CMB. I don't get it, it should be everywhere.

S

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#31
In reply to #30

Re: Relativity/Cosmology FAQ

03/24/2008 1:46 AM

Hi S.

The CMB photons (at ~2.7°K) that we now observe are only those emitted in the very, very early universe, near the observable horizon - the later/closer CMB photons have passed us and will never be seen again.

If we were static in this (CMB) frame of reference, we would have observed exactly the same temperature in all directions, but there is a distinct dipole in the observed temperatures, indication our movement relative to the CMB frame.

Regards,

Jorrie

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#32
In reply to #31

Re: Relativity/Cosmology FAQ

03/26/2008 8:06 PM

Hi Jorrie,

Can you tell us how this measurement is made?

So if we are measuring to something that was billions of years ago, then we are comparing our motion to what it was then. With all the gravitational attraction, that should be no surprise, so what does it really tell us? We know that there is no absolute motion - Newton and Einstein both agree on that.

S

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#33
In reply to #32

Re: Relativity/Cosmology FAQ

03/27/2008 11:36 AM

Hi S.

The anisotropy of the CMB is usually determined using a differential microwave radiometer, with two antennas pointed at different regions of sky. It was first done from balloons, later from U2 spy planes and finally from satellites (COBE and WMAP). See George Smoot's – 'Wrinkles in Time', or just Google the two satellite names.

You asked: "So if we are measuring to something that was billions of years ago, then we are comparing our motion to what it was then."

We are comparing our present motion to the average frame of the universe then, not our own motion then!

"We know that there is no absolute motion - Newton and Einstein both agree on that."

Agreed, but the 'rest frame of the observable universe' is as close as we can come! It is used in cosmology as a sort of "preferred frame", if you like, but it still does not allow absolute motion.

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Jorrie

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#34
In reply to #33

Re: Relativity/Cosmology FAQ

03/29/2008 12:50 AM

Hi Jorrie,

That's pretty cool. I can see why astronomers would want a reference frame. When you think of the expansion of the universe over those billions of years, the CMB is kinda like a 'center point' of the universe even though it doesn't have one.

regards,

S

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#35

Re: Relativity/Cosmology FAQ

08/24/2008 12:53 AM

Jorrie you have the patience of a saint! I just started viewing lectures about relativity and quantum mechanics about a month ago so naturally I consider myself somewhat of a expert. No seriously when does the learning end because I'd like to start solving all the problems and of course prove Einstein wrong.

Anyways, it's tough to explain why there's no point zero. People see a bomb go off with chaotic debris scattered in all directions yet they can see there was a center to the explosion. What they can't imagine is how it would look like from inside the bomb. There is no center to the explosion inside the bomb because everything goes off at once. The particles explode away from each other. Even the bomb casing, which can be likened to the cosmic background radiation (CMB), explodes away from the particles in all directions. When they show pictures of the universe expanding away from the CMB, they represent it as a small globe from which the universal acceleration can look back on to a central point. This just adds to the confusion. We are the particles looking out in all directions from inside the bomb at the shell casing which is speeding away from us in all directions. It's not a small globe, it's the biggest globe. The small globe is what it looked like 14 billion years ago and we were still inside it then.

I tried explaining the same idea with the old expanding balloon model. I said look at the two dimensional skin of the balloon and mark dots on it. when you blow up the balloon, the dots all move away from each other. Now just extend that 2 dimensional skin to give it a 3 dimensional thickness like smearing a thick gel on it. Watch as the bubbles inside the gel all move away from each other as you continue inflating the balloon. The answer was invariably, "You're an idiot, everything's expanding away from the center of the balloon." I don't have your patience. However, I will be testing your patience by bombarding you with questions. Hopefully on not so basic a level.

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#36
In reply to #35

Re: Relativity/Cosmology FAQ

08/24/2008 10:00 AM

Now i confused myself. The CMB is everywhere like letters on a big page. Anywhere you center your magnifying glass (the observable universe) on that page, you'll see letters going off in all directions from the center. You won't see the same letters but the CMB will always be at the fringes of your magnifying glass. But there's also an expanding sphere of quasars preceding the CMB sphere. If you live at the center of that quasar sphere, you'll see quasars equidistant from you. If you live at the edge of that sphere, you'll see a rim of quasars like the milky way. This is how you'll know you're not at the center of the universe. So if you take your magnifying glass and center it at a point where everywhere on the rim is the letter Q (for quasar), you have found point zero. No?

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#37
In reply to #36

Re: Relativity/Cosmology FAQ

08/25/2008 8:25 AM

Hi ralfcis, you wrote: "If you live at the edge of that sphere, you'll see a rim of quasars like the milky way. This is how you'll know you're not at the center of the universe. So if you take your magnifying glass and center it at a point where everywhere on the rim is the letter Q (for quasar), you have found point zero. No?"

No. We see the quasars as they were more than 10 billion years ago. Some observer that is now living where we saw the ancient quasars, will see no nearby quasars and to her the universe will look much like how we see it (with CMB and ancient quasars at large distances).

Jorrie

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#38
In reply to #37

Re: Relativity/Cosmology FAQ

08/25/2008 9:06 AM

Sorry, I threatened you with a bombardment of questions but I won't do it until I've read all the posts in case you've already answered them. Anyways, I'm trying to understand your answer. Are you saying the picture of the quasars is 10 billion years old and we've moved on since then and we can't correlate where we would have been 10 billion years ago to have seen that picture now? So time is making the distance measurement impossible? Light would need to be instantaneous to find point zero? This is way more difficult to comprehend than I thought.

But wait, wouldn't someone out there at point zero see no movement over time with respect to the center of the expanding sphere of quasars?

So my analogy to the bomb casing being the CMB was also wrong. The CMB is actually the flash of light in all directions within the bomb as it explodes?

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#40
In reply to #38

Re: Relativity/Cosmology FAQ

08/26/2008 1:25 PM

Hi ralfcis, you wrote: "But wait, wouldn't someone out there at point zero see no movement over time with respect to the center of the expanding sphere of quasars?"

There is no "point zero" or "center point" in the 4 dimensions (3+time) that we can observe. The "inside of the balloon" does not exist as we far as observables are concerned.

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#41
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Re: Relativity/Cosmology FAQ

08/26/2008 1:44 PM

Thank you. So I need to be able to visualize what spacetime looks like. If it was just 3D space then point zero would be at the center of the quasar sphere? I keep seeing the word flat universe with some sort of non-edge, is that spacetime? Then yes, there is no center point to a thing like that. It looks like I have a lot more reading to do.

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#42
In reply to #41

Re: Relativity/Cosmology FAQ

08/27/2008 9:04 AM

I'm up to the point of understanding that I've never seen in 3 dimensions plus time even though I exist in a 3D spacetime. My vision is actually 2D plus time to give me the illusion of 3 dimensions. I'm basically seeing a series of 2 dimensional slides which are slices of time to give me the illusion of depth perception. I can't understand what I'd be seeing if I was really able to perceive 3 dimensions plus time.

Hence, if you use the 2D balloon analogy for a 2D spacetime universe, the center of the expansion (the balloon center) is completely outside the 2D spacetime universe. A 2D person would never be able to detect something outside his universe. The same analogy would apply to our 3D spacetime; No possibility to detect the center. It's ironic that I thought people were dumb for not understanding the balloon analogy and I didn't even understand it.

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#44
In reply to #40

Re: Relativity/Cosmology FAQ

05/30/2009 10:22 PM

If we can measure our speed relative to CMBR which is 0.002c, it is logical to assume that at different places of the universe beings (if there are any) will measure a differnt speed relative to CMBR. So, the center of the universe is where the beings measure speed=0 relative to CMBR.

This is elementary Dr. Watson.

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#45
In reply to #44

Re: Relativity/Cosmology FAQ

05/30/2009 11:44 PM

Hi Guest.

The ~0.002c that we measure as the peculiar velocity of our galaxy is unique to our local conditions, being pulled by some large concentration of mass (the Great Attractor) off the Hubble flow (meaning at rest relative to the CMBR).

Every other galaxy in the universe could have a similar situation, but at some different peculiar velocity. There are probably also many galaxies with zero peculiar velocities, but no, they are not at the center of the total universe.

If we use the expanding balloon analogy, such galaxies sit stationary relative to the surface of the balloon, while we (and most other galaxies) are moving relative to the surface of the balloon, representing peculiar velocity. Every galaxy is obviously at the exact center of its own observable universe, which is only part-way around the balloon due to the finite speed of light.

Hope this helps!

-J

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#46
In reply to #45

Re: Relativity/Cosmology FAQ

05/31/2009 9:24 AM

Dear J,

that is the standard answer, the talking points of G Relativists. However, the latest observations claim that the universe is flat. You cannot use the baloon example on the flat universe. This is not a reasonable logic. It is simple politics (meaning lie) to switch from one model to another when the situation requires it.

Thanks to peculiar motion we can explain everything. Seems just like another epicircle.

Best regards. Guest.

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#47
In reply to #46

Re: Relativity/Cosmology FAQ

05/31/2009 11:45 AM

Hi Guest, you wrote: "However, the latest observations claim that the universe is flat."

Note that there is a higher probability in the data that the universe is just closed, but the uncertainty in the data also includes a flat universe.

You said: "You cannot use the baloon example on the flat universe."

The balloon analogy is just a popularization of the more general hyper-spherical model, which incidentally can accommodate closed, flat and open universes. It is compatible with all present data, but it does not explain everything - it is just a model compatible with what we observe. It does not say why things work like they do.

-J

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#48
In reply to #47

Re: Relativity/Cosmology FAQ

05/31/2009 2:29 PM

Dear J,

Now your answer is even more confusing. Let me say it another way. If the universe is flat or close to flat, then the local patch (what we observe) of space time is Euclidian and when we observe the sky we see CMBR distributed uniformly around us. So, the local flat visible universe is a sphere which has a center and our Earth is not too far from it.

Best regards,

Guest.

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#49
In reply to #48

Re: Relativity/Cosmology FAQ

05/31/2009 3:01 PM

Hi again Guest, you wrote: "So, the local flat visible universe is a sphere which has a center and our Earth is not too far from it."

But this is what I said in reply #45 above: "Every galaxy is obviously at the exact center of its own observable universe, which is only part-way around the balloon due to the finite speed of light."

Note that the hyper-sphere is 4-dimensional, spatially (actually four space and one time). The 4th spatial dimension itself is not observable; only the curvature of 3-d space into the 4th dimension is observable in principle. In order to visualize, we usually ignore one normal spatial dimension, so that we have a 2-d surface that may or may not curve into the 3rd dimension (hyper-space). If space is flat, the hyper-radius is actually undetermined (one might say infinite, but that's also not quite correct). Nevertheless, the hyper-spherical model handles it just fine...

-J

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#50
In reply to #49

Re: Relativity/Cosmology FAQ

05/31/2009 5:52 PM

Hi J,

More relativity speak. I realy like the unobservable thing . Let's drop those from the discussion. We can measure the curvature of the 2D sphere by running on it in circles and measure the surface area and the circumference. The same thing can be done in the 3D sphere. The result is that it is flat, not a surface of the curved 4D sphere. If it is flat and we see the uniform CMBR, we are about in the center and other galaxies are running away from us, some of them at a pretty good clip. Those are not in the center. This is the fact of the flat geometry and observation. You cannot claim that beings in them see the same CMBR, since we see a motion relative to CMBR equal to 0.002c. You cannot claim without evidence that they all see 0.002c. If you claim that they all see 0c and all are in their centers, this is just another hyphothesis that needs proving, not just a belief. The hyphothesis that the universe looks the same from every point is jus that, the hyphothesis, not the truth. This needs to be proven first.

Best regards, Guest.

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#51
In reply to #50

Re: Relativity/Cosmology FAQ

05/31/2009 9:53 PM

Hi Guest.

Most of what you wrote is in conflict with standard, mainstream cosmology. You are welcome to write about your views, but then I would prefer that you start a new thread on that (you need to log in to CR4 or register, it you haven't done so).

This thread is a FAQ on standard relativity and cosmology and to prevent confusion, that is the way it should stay. If you have a proper "new theory", I do have an open thread on that, called "Alternative Cosmologies", but it has some broad rules as well. From what I gather so far, your best route is a new thread on CR4 (or on some other forum of your choice).

I hope you understand my concerns.

-J

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#39

Re: Relativity/Cosmology FAQ

08/26/2008 12:14 AM

Damn, I haven't finished reading all the posts but I'm going to ask my questions anyway:

1. So big bang says the CMB is a result of universal expansion stretching out the wavelength of the initial high energy photons released at .4Gyr? So why are we able to SEE the first galaxies created? Wouldn't their light also be stretched to microwave or infra red and not just a tiny red shift as observed? In other words if the CMB is like a massive red shift of the big bang, why don't smaller bangs right after show a comparable huge red shift?

2. The early universe must have taken time to clear up and organize. Gravity would have taken billions of years to organize the highly energetic, light and scattered first particles as it takes billions of years to form stars in galactic disks. Without large expanses of vacuum, light would have been significantly slowed and scattered by the particles. Yet we see crystal clear images of 13 billion year old galaxies with large voids in between. I don't understand how variations in the CMB are responsible for galaxy formation. Gravity was way overmatched in the early stages which would have spewed out a huge gas dispersion. Even old galaxies can't swallow or organize their own gas disks even after billions of years.How were the voids created so quickly? How did the universe get so clean so fast? The CMB would have had to have been way more irregular.

3. Does the size of the universe affect universal constants?

4. Big bang also explains Olber's paradox by saying galaxies beyond our event horizon can't contribute to light pollution. Has anyone actually added up the luminosity of the visible stars and compared it to the actual luminosity of the visible universe. Is the result in line with big bang predictions? It seems way too dark out there.

5. Is it true that some deep field galaxies are actually blue-shifted? How if they're going like .9c away from us.

6. The universe favors light elements. However, if fusion stops at iron, how were the heavier elements formed if not in the ultra powerful big bang?

7. Pictures of galaxies colliding show increasing supernova activity in the disks of spiral galaxies indicating the gravitational perturbations are causing the gas to condense and fuse. There are also pictures of elliptical galaxies or globular clusters (galaxies without disks) spewing out vast gas clouds perpendicularly into space. Why is the void between galaxies not full of particles that are spewed out of galactic cores and disk supernovae? The galaxies don't have enough power to sweep these areas clean because they can't even suck in their own disks. We know the areas are clean because light is not foggy from distant galaxies. Entropy shows gas released in a vacuum will fill the vacuum evenly.

8. If dark matter is the gravitational glue that makes galaxies spin like solid disks then it must be right in close with galactic matter and should also glue the planets in our solar system to spin like a solid disk. I think all the dark matter was swept out by antigravity-gravity repulsion into a galactic halo which acts like an external clamp (not internal glue) on the galaxy. The anti-gravity should cause bumps in space-time (as opposed to dimples) which would be seen as an opposite lensing effect. Also since dark matter looks like a scattered "electron cloud" around a galactic nucleus, it looks like anti-gravity scatters its particles (there don't seem to be any dark holes indicating dark matter coalesces) and would push against other halos to accelerate universal expansion. The super scattering of dark matter would produce white holes which would look like total voids in space.

9.Measurements on spiral galaxies show the arms move as fast as the centers. I believe this is because the dark matter halo acts like an external antigravity clamp that holds the galaxy together. However, the spiral arms indicate that at one time the galactic core was spinning faster than the disk. I believe that time was before the dark matter was swept out of the galactic center by the scattering power of antigravity (dark energy). If this is true, then deep field galaxies should still show radial arms lagging the center because they're too young to have all the dark matter swept out.

10. I still cannot grasp why if the Michelson morely experiment was searching for a medium for light and none was found, how did someone subsequently explain light doesn't need a medium. Is the medium the photons themselves? Does the wave propagation depend on the alternating electromagnetic field? This isn't a medium.

11. If you need gluons to hold nuclei together and they're some sort of jelled energy that has mass, why are some nuclei atomic weights less than the some of their integral protons and neutrons eventaking into account that carbon 12 is the convention used to calculate atomic weights.

12. If space is defined by what's in it then how is it possible that the same particle can occupy two different spaces and generate a real interference pattern in the double slit experiment? How is this explained without redefining space (like a single space can also be two different spaces simultaneously)? Does this mean space itself is uncertain? If a single particle can occupy two different spaces simultaneously, can entangled particles be considered a single particle occupying two different spaces simultaneously. This would explain entanglement because you're only really affecting one particle (that looks like two) in one space (that looks like two). The converse is also true with the Pauli principle. Two particles can occupy the same space so long as they have different quantum numbers. Hence a single particle occupying one space can decay into two oppositely spinning entangled particles. Seems way too symmetrical to not believe there are 4 different definitions for space (1 particle per space, 2 spaces per particle, 1 particle for 2 spaces and 2 entangled particles in 2 spaces. I mean space has been redefined, why not redefine the particle as well. Why is the number 2 magical? Why can't 3 or more particles be entangled or 3 or more spaces be occupied by the same particle? Is 2 magical because the universe must be based on 50/50 randomness to exist? If it wasn't based on 50/50 randomness, probability theory shows that the bigger the stake in a casino with unbalanced odds, the surer the game will end. But there is an imbalance in the production of matter over anti-matter. Is this the seed to the universe's destruction?

13. Since Einstein used probability (and knew how casinos worked) to prove his quantum and atomic theories, I'm curious why he didn't realize that the only way to have a certain universe was to base it on perfect uncertainty (probability). I'm surprised that Einstein who used probability to prove at least 4/5 of his 1905 papers, could then turn around and claim god does not play dice with the universe.

14. Does entanglement disprove Heisenberg? I mean if you measure the position of one of the particles and the motion of the other then you do know both position and motion of both particles because they're entangled. Does annihilating one of the entangled pair automatically annihilate the other at a distance?

15. If a free positron and a free electron join because of electromagnetic attraction do they then annihilate on contact? It's the same question for an electron landing on a proton. Do they automatically become a neutron? So what force keeps them from coalescing? I assume they must be rammed together but why doesn't that ramming energy just generate the same glue particles that hold the nucleus together and glue in electrons to the surface of protons?

16. I also found the lectures on the purpose of the universe as a physical medium to store information very interesting. Also that you don't need to know all the information stored, just a RANDOM sample to get the result you need. As a philosophical question, could that information and the mathematics used to deploy it have existed before the medium existed? Is the medium the message or is the message the message? Are concepts real even though they're intangible? Certainly ideas can be brought into reality so why aren't ideas real? Way off topic, you don't need to answer.

17. I don't get gravity at all so you don't need to answer this question. If it's no longer a force at a distance and just a curvature of space time, why are they trying to unite it with the other forces. It doesn't act like two charged objects that increase the speed at which they hit each other based on their charges. A bowling ball moves as fast as a golf ball so the more mass in one makes no difference. Their movement just follows the curved lines of spacetime. If mass creates gravity by warping spacetime, would a warp in spacetime create mass?

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#52
In reply to #39

Re: Relativity/Cosmology FAQ

06/10/2011 3:25 PM

ralfcis you have certainly stopped the flow of garbage for a moment. Some excellent probing questions. High time that Einstein no longer ruled. He had his day but we should have wised up by now - nothing but imagination and maths has contributed to astrophysics since. Where are all the experiments, (apart from Cern, etc money burners) to falsify or otherwise the plethora of invisible entities invading our minds?

Too many assumptions have failed to be challenged. At least I am assuming these are the assumptions eg:

  1. Gravity is limited by light speed
  2. Redshift only indicates speed/ distance
  3. The weakest force, gravity, is the ONLY one building the Universe
  4. Black Holes exist
  5. Dark matter exists
  6. Stars work on nuclear fusion
  7. Magnetism can exist without electric current
  8. Plasma is a by-product of hot gases
  9. Moving elementary particles are winds
  10. The Big Bang started everything off, unaided!
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#53

Re: Relativity/Cosmology FAQ

03/26/2016 2:46 AM

This is test, so please ignore

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