How do we see "old" galaxies?

[zapatos]

If the universe is 14 billion years old, how do we see a galaxy that is 10 billion years old?

 

From the time of the big bang, if travelling at the speed of light, it would have taken that galaxy (or its components) 10 billion years to get that far away from us. Then for the light to get from there to us would take another 10 billion years. That is a total of 20 billion years elapsed, yet the galaxy is only 14 billion years old.

 

Can someone explain to me the flaw in my logic? Thanks.

[AzurePhoenix]

When we look out 10 billion light years away at a galaxy, we're not looking at it as it is now, but as it looked ten billion years ago when it was still quite young, while it's gone on to mature and develop in the interim. Likewise, the Andromeda Galaxy which is just as old as any of those distant galaxies is only about 2.5 million lightyears away, so we see it nearly as old as it is with far less delay. Also keep in mind that any distant galaxy is actually much further away by now than it visibly appears because of the accelerating inflation of space in the universe. Off the top of my head I think the visible "edge" of the universe, which looks about 13+ billion lightyears away is actually something more like 40 some billion lightyears away. And of course that's only the universe within our horizon of sight.

[Cap'n Refsmmat]

From the time of the big bang, if travelling at the speed of light, it would have taken that galaxy (or its components) 10 billion years to get that far away from us. Then for the light to get from there to us would take another 10 billion years. That is a total of 20 billion years elapsed, yet the galaxy is only 14 billion years old.

 

Can someone explain to me the flaw in my logic? Thanks.

Adding to what Azure said, it's worth noting that the light was emitted 10 billion years ago, when the galaxy was much, much closer to us.

[zapatos]

Ok, but if we see the galaxy as it was 10 billion years ago, that means the light we are just now seeing has been travelling toward us for 10 billion years, which means the galaxy was 10 billion light years away from us when the light we are now seeing was emitted from that galaxy. Isn't that correct?

 

And we know that at the time of the big bang, all matter was in the same place. And I assume it took at least 10 billion years for that galaxy to get 10 billion light years away from us. Correct?

 

So if it took 10 billion years for that galaxy to get that far away from us, and another 10 billion years for the light to get back to us, then doesn't that mean the universe is at least 20 billion years old? But isn't the universe believed to be only about 14 billion years old?

[divagreen]

So if it took 10 billion years for that galaxy to get that far away from us, and another 10 billion years for the light to get back to us, then doesn't that mean the universe is at least 20 billion years old? But isn't the universe believed to be only about 14 billion years old?

 

I think I see where you are going with this, and while I hate to answer a question (especially one where I don't know the exact answer to) with a question, I do ask this...can the galaxy that is moving away from us still be emitting light that we would be seeing? Wouldn't that cut down on all of that travel time?

 

Wouldn't that mean we are just seeing light from that galaxy that is 10 billion light years away, mean that we are just seeing light from that galaxy that is 10 billion years away? Isn't there a point where the space curvature intercepts or even supersedes expansion and general relativity with regards to time?

 

I am a novice when it comes to cosmology.

[michel123456]

All those kind of questions are answered by the inflation theory.

Inflation theory explains how galaxies were placed "magically" so far away from each other in so little time. http://en.wikipedia.org/wiki/Inflation_(cosmology)

 

 

 

Also you could ask yourself how is that possible that an entire galaxy could form in only 3 or 4 billions years. Mainstream scientists are struggling with this question, because we are observing what we believe be old galaxies in a very young position in the universe. Some of the many articles on the subject http://physicsworld.com/cws/article/news/19826

http://www.sciencedaily.com/releases/2008/04/080401160020.htm

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I am a novice when it comes to cosmology.

 

Go to http://www.scienceforums.net/forum/showthread.php?t=35925, begin reading post #10 (the last one), at least.

 

I had once some argument with Martin...

Edited May 19, 2010 by michel123456
stupid comment

[Airbrush]

If the universe is 14 billion years old, how do we see a galaxy that is 10 billion years old?

 

From the time of the big bang, if travelling at the speed of light, it would have taken that galaxy (or its components) 10 billion years to get that far away from us. Then for the light to get from there to us would take another 10 billion years. That is a total of 20 billion years elapsed, yet the galaxy is only 14 billion years old.

 

Can someone explain to me the flaw in my logic? Thanks.

 

The universe is less than 14 Billion years old. We can see galaxies up to a distance, measured in YEARS, of light we see now that is about 13 Billion YEARS OLD. And that is not 13 Billion light years away. That galaxy was much closer to us when the light left it. We can even calculate how far away from us it was when the light, we see now, left it. That galaxy is about 30 Billion light years away from us NOW. The cosmic background radiation is the most distant thing we can detect, and that is about 45 Billion light years away from us NOW.

 

Review the Ned Wright Calculator under the sticky topic "Cosmo Basics" by Martin. Maybe someone can explain how it works.

 

At one time Martin helped us use the calculator, but I forget how. It is not very friendly to cosmo beginners, such as me. You need to know red-shift values. Someone should create a more user-friendly calculator, using light years instead of gigaparsecs.

 

http://www.astro.ucla.edu/~wright/CosmoCalc.html

Edited May 19, 2010 by Airbrush

[Spyman]

If the universe is 14 billion years old, how do we see a galaxy that is 10 billion years old?

 

From the time of the big bang, if travelling at the speed of light, it would have taken that galaxy (or its components) 10 billion years to get that far away from us. Then for the light to get from there to us would take another 10 billion years. That is a total of 20 billion years elapsed, yet the galaxy is only 14 billion years old.

 

Can someone explain to me the flaw in my logic? Thanks.

 

Imagine that you are holding a rubber band stretched between your hands and balancing a wheel on it. Lets say that the radius of the wheel is such that it takes ten turns for it to travel from one hand to the other. Now if you streach the band to twice its length it would take twenty turns for the wheel to traverse from one hand to the other.

 

Here is the kicker, what happens if you streach the rubber band while the wheel is traversing?

 

Answer: You will end up with three different distances, one for the distance between hands when the wheel starts its journey, second is the distance between your hands when the wheel finishes its trip and thirdly the distance the wheel has traversed on the rubber band, measured in number of turns.

 

----------

 

Space is expanding like the rubber band and the speed of expansion is not limited to the speed of light, in fact it is often greater and during the initial phase of the Big Bang it was huge.

 

When it's mentioned that a galaxy is 10 billion lightyears distant, it is the age of the light they are talking about which also is the distance the light has traveled from that galaxy to us, like the wheel. But the galaxy was closer to us when the light we see was emitted and is farther away right now when we are recieving the light.

 

When space expands lightrays traveling through it gets streached too, and that gives them a redshift which astronomers can measure and use to calculate their distance and "displacement" due to expansion relative us.

 

----------

 

Here is a good Cosmos calculator you should test: http://www.uni.edu/morgans/ajjar/Cosmology/cosmos.html

 

You need to input these values: Omega=0.27, Lambda=0.73, Hubble=71 and Redshift=1.815 for a galaxy with 10 billion lightyears old light, but you can play around with the redshift and check out different ages for the lightray. If you change the Hubble value you will be able to check different ages of the Universe.

Edited May 20, 2010 by Spyman
Needed small corrections

[michel123456]

Imagine that you are holding a rubber band stretched between your hands and balancing a wheel on it. Lets say that the radius of the wheel is such that it takes ten turns for it to travel from one hand to the other. Now if you streach the band to twice its length it would take twenty turns for the wheel to traverse from one hand to the other.

 

Excellent description.

The thing I can never swallow with these kind of figures, is that in reality, the rubber band is made of void. The same void that we encounter inside matter, between protons & electrons, between quarks.

In my understanding, if you want to stick to the rubber band analogy, you have to take a wheel made from rubber, and stretch the wheel too.

In the standard model, it is not the case, it is considered that the wheel is not submitted to the stretching. I have some difficulties on that point.

[Spyman]

Excellent description.

The thing I can never swallow with these kind of figures, is that in reality, the rubber band is made of void. The same void that we encounter inside matter, between protons & electrons, between quarks.

In my understanding, if you want to stick to the rubber band analogy, you have to take a wheel made from rubber, and stretch the wheel too.

In the standard model, it is not the case, it is considered that the wheel is not submitted to the stretching. I have some difficulties on that point.

I said:

When space expands lightrays traveling through it gets streached too, and that gives them a redshift which astronomers can measure and use to calculate their distance and "displacement" due to expansion relative us.

So if the lightray is "the wheel" then it is affected as "made from rubber".

 

 

But if you mean that objects made of matter don't swell due to expansion, I think that it is considered that they do, but the measurable expansion in space takes place over tremendous vast distances while the distances on atomic level is infinitesimal puny.

 

If the force from Dark energy expanding space is acting inside matter too, slightly increasing the distance between particles, then on this scale the nuclear forces are large compared to the force from Dark energy which is dwindling down to a vanishingly tiny level.

 

The particles are "placed" inside matter with a distance that is due to the nature of the nuclear forces and when the force from Dark energy is offsetting the distance, this offset only causes the nuclear forces between the particles to rebalance with a slightly larger distance.

 

When comparing the distance between two particles in an expanding space and a non expanding space the differense is insignificant and negligible. We are not able to measure so diminutive distances and even if we could we don't have a lab with non expanding space to compare with.

Edited May 21, 2010 by Spyman
Small correction

[michel123456]

(...)

 

But if you mean that objects made of matter don't swell due to expansion, I think that it is considered that they do, (...)

 

I was unaware of that. I thought it was not considered at all.

 

The void between the protons and the electrons is not tiny respectively to the proton dimension.

 

Searching the web for a representation to scale.

 

Here:

1. Size relationships of subatomic particles

a. If the nucleus were the size of a period (.) the atomic diameter would be

about 5 m. (The volume of the nucleus is about 1/100,000 the volume of

the entire atom.)

b. If the nucleus of an atom were the size of a baseball, the atomic diameter

would be about 4 km. The electrons would each be smaller than a period (.)

and would move about at random in the spherical region between the

nucleus and the edge of the atomic diameter.

from http://intro.chem.okstate.edu/chemsource/atomic/concpt3.htm

Edited May 21, 2010 by michel123456

[Airbrush]

Thanks for the size relationships of subatomic particles, Michel. I will try to remember those and consider the incredible scales.

 

A sheet of paper is 1,000,000 atoms thick. And the proton is a tiny speck inside a huge area of empty space. What a brain sizzler!

[michel123456]

I am still searching where I did I read an analogy of distances inside the atom with distances between planets.

It is very instructive to understand that all stuff is made of a tremendous incommensurable huge quantity of void (can we say that?).

 

Of course that does not negate what Spyman said.

 

Because in physics, distance is not a relative thing. Distance is considered as an absolute concept. Distance begins at Planck length and goes up to infinite.

 

In physics dominated by Relativity, distance remains absolute.

[Nano]

Haha. So funny. I haven't been visiting this site since forever. The only reason I was loggin on again was that I was thinking the exact same question as the thred-starter. Turns out he read my mind.

 

If I understand it right, the answer to the question is:

The universe has been, and is expanding with a velocity close\at (faster?) than the speed of light, relative to us. And that is why galaxies that were close to us in the past still uses 10Billion LY to reach us. The light doesn't quite "catch up" to the speed of the universes expansion, which has a direction the oposite way than that of the light.

 

But one thing I don't get about this, is that c is fixed no matter how fast the observer is moving. Right? That means that the light on it's way to us must have had a constant speed at c, not dependent of if space around it is moving in oposite direction. Then how can the expansion of the universe have any influence on the lights' speed?

Edited May 22, 2010 by Nano

[PaulS1950]

 

But one thing I don't get about this, is that c is fixed no matter how fast the observer is moving. Right? That means that the light on it's way to us must have had a constant speed at c, not dependent of if space around it is moving in oposite direction. Then how can the expansion of the universe have any influence on the lights' speed?

 

The speed of light remains a constant but if the space it travels through is expanding it has to travel farther to get to the distant observer (us).

[J.C.MacSwell]

Ok, but if we see the galaxy as it was 10 billion years ago, that means the light we are just now seeing has been travelling toward us for 10 billion years, which means the galaxy was 10 billion light years away from us when the light we are now seeing was emitted from that galaxy. Isn't that correct?

 

 

Definitely not correct.

[Realitycheck]

Lets say that 10 billion years ago in that galaxy's time, this event happened that we are just now seeing in our telescope. However, we have been traveling/expanding in different directions all of this time. We know that when that event occurred, it must have been much closer to us, say, 6 billion light years, because the space/matter here has been expanding into some other direction than that space/matter. Since we have been expanding in different directions, it is safe to assume that the light was not going to reach us in a straight line, but rather it was going to meet us at an intersecting point based on all of the corresponding variables of directions and distances and speeds, etc. Since we have been travelling in different directions, the light has had to travel a greater distance and has taken longer to get here. If we were traveling/expanding in exactly opposite directions, I think it is safe to assume that we will never be able to see these objects because the further we grow apart, the greater the expansion speed gets, until the effective speed of expansion exceeds the speed of light, and it will never be able to reach us unless the universe stops expanding or perhaps starts retreating into a crunch. Am I right or am I right?

Edited May 23, 2010 by agentchange

[Spyman]

...Since we have been expanding in different directions, it is safe to assume that the light was not going to reach us in a straight line, but rather it was going to meet us at an intersecting point based on all of the corresponding variables of directions and distances and speeds, etc. Since we have been travelling in different directions, the light has had to travel a greater distance and has taken longer to get here...

No, this is wrong and not the current scientific explanation. The Big Bang was NOT an explosion of matter that flung apart pieces through space in different directions from a central point.

 

According to observation, everything at large distances are expanding apart from us equally in all directions. If we look at any distant galaxy which are swept away from us due to expansion, the distance is increasing in directly opposite direction from us, there is no intersecting path of light through the three normal dimensions of space as if we where moving through space at different trajectories.

 

If the Universe continues to expand at an accelerated rate there will be less and less matter left within our observable part of it, since the expansion already exceeds the speed of light at greater distances.

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The void between the protons and the electrons is not tiny respectively to the proton dimension.

A recent value for the Hubble constant is around 71 km/sec/Mpc which gives an expanding speed of 2.3×10^-12 m/s per meter and the Helium atom has an electron cloud with a diameter of around 1×10^-10 m so on this scale the expansion of space is 2.3×10^-22 m/s without any forces at all countering it.

 

Size comparison:

a) If the atomic nucleus was 0.05 mm and the cloud was 5000 mm then the expansion for the electron from the core would be of 0.0000000115 mm/s without counter forces.

b) If the nucleus was 400 mm and the electron some 4 000 000 mm distant then it would move away from the nucleus with 0.0000092 mm/s, without counter forces.

 

I think we can safely conclude that the forces causing expansion is not affecting the sizes of atoms much.

[michel123456]

It is the first time I see such a reasonning, Spyman. Usually, it is considered that the expansion of space counts only for large distances between galaxies or even between clusters of galaxies, and not for interstellar distances, certainly not for distances inside atoms.

[Spyman]

Yes, it is normally considered that the expansion of space only happens on very very large scales.

 

But, as I have tried to explain, on smaller scales, things like galaxies, solar systems, molecules and atoms are bound systems, they are held together by forces much stronger than the expansion. The force from Dark energy is not able to continue to expand them, instead bound systems only expands until they reach a slightly larger size where the forces that holds them together counter and stop the expansion.

 

So bound systems don't continue to expand but they are a tiny bit larger due to Dark energy, this tiny bit is so teeny-weeny that it is not measureable and esteemed unimportant.

 

 

The reasoning is not my personal idea, it's a valid scientific conclusion and even mentioned on Wikipedia:

 

"A cosmological constant has the effect of a repulsive force between objects which is proportional (not inversely proportional) to distance. Unlike inertia it actively "pulls" on objects which have clumped together under the influence of gravity, and even on individual atoms. However this does not cause the objects to grow steadily or to disintegrate; unless they are very weakly bound, they will simply settle into an equilibrium state which is slightly (undetectably) larger than it would otherwise have been."

http://en.wikipedia.org/wiki/Metric_expansion_of_space

[michel123456]

Isn't it then a 5th force of nature?

[Spyman]

Nature of dark energy

The exact nature of this dark energy is a matter of speculation. It is known to be very homogeneous, not very dense and is not known to interact through any of the fundamental forces other than gravity. Since it is not very dense — roughly 10⁻²⁹ grams per cubic centimeter — it is hard to imagine experiments to detect it in the laboratory. Dark energy can only have such a profound impact on the universe, making up 74% of universal density, because it uniformly fills otherwise empty space. The two leading models are quintessence and the cosmological constant. Both models include the common characteristic that dark energy must have negative pressure.

http://en.wikipedia.org/wiki/Dark_energy

Edited May 25, 2010 by Spyman
Fixing exponent

[michel123456]

it is hard to imagine experiments to detect it in the laboratory.

Yes, but not because it is so tiny.

the reason is because the lab itself, the microscope and the laboratorian himself are under the power of the same force of expansion.

Isn't it?

[Nano]

It is known to be very homogeneous, not very dense and is not known to interact through any of the fundamental forces other than gravity.

 

What does it mean that dark energy interacts through gravity?

[Spyman]

Yes, but not because it is so tiny.

the reason is because the lab itself, the microscope and the laboratorian himself are under the power of the same force of expansion.

Isn't it?

The values are small enough to be far below our observable limit with current technology, but I think there would also be problems with finding reference points and couping with equipment being affected by the phenomen under measurement.

 

 

What does it mean that dark energy interacts through gravity?

In the theory of general relativity both energy and matter bends the geometry of spacetime which causes gravity, thus if the vacuum energy of empty space is negative, it would bend spacetime in the opposite directions as positive energy or mass, which would be like a gravitational repulsion.