Misconceptions about the Big Bang in Scientific American March 2005
This document contains comments about the article Misconceptions about the Big Bang by Charles H. Lineweaver and Tamara M.Davis In Scientific American of March 2005.
To read the article select:
In this copy the 10 pages are numbered from 36 to 45. In the original Scientific American magazine they are numbered from 24 to 33. I will use the copy numbering.
- The text in italics is copied from the article
- Immediate followed by some comments
The expansion of the universe may be the most important fact
In this paragraph we read:
Renowned physicists, authors of astronomy textbooks and prominent popularizers of science have made incorrect,
misleading or easily misinterpreted statements about the expansion of the universe.
If you made such a statement you should be more specific what good practices, what bad practices are, what correct and what incorrect means.
Sometimes it is important to say: We are not sure.
Expansion is a beguilingly simple idea, but what exactly does it mean to say the universe is expanding?
If you do not what "expanding" means you can not claim that it is simple. Any way what means simple?
Is Earth expanding, too?
The answer in the article about galaxies is Yes and No. (See Is Brooklyn Expanding?) But how do we know that that is correct?
To add to the befuddlement, the expansion of the universe now seems to be accelerating,
But how do we know that that is correct?
What is Expansion, Anyway?
The universe does not seem to have an edge or a center or an outside, so how can it expand?
What is the definition of Universe ?
How do we know that the Universe expands ?
In fact we do not know that the Universe expands. What we know that on average the galaxies are moving away from us based on observations ie a shift in received frequencies. As a result you can claim that our local universe expands, but you can not conclude that the universe at large expands.
A good analogy is to imagine that you are an ant living on the surface of an inflating balloon. Your world is two-dimensional; the only directions you know are left, right, forward and backward.
The problem is there exists no two dimensional world. That means you can not use this analogy as a description of the processes that take place in our local universe.
Individual galaxies move around at random with in clusters, but the clusters of galaxies are essentially at rest.
Individual galaxies move around under the laws of gravity ie in a simple scenario as described by Newton's Law.
The term “at rest” can be defined rigorously. The microwave background radiation fills the universe and defines a universal reference frame,
The problem is we are not at rest with this reference frame.
Ubiquitous Cosmic Traffic Jam
Thus, the big bang was not an explosion not an explosion in space; it was more like an explosion of space.
When you have a certain area filled with objects then the area between those objects is called space ie empty space
How can space explode?
It did not go off at a particular location and spread out from there into some imagined preexisting void. It occurred everywhere at once.
And what does this everywhere mean?
Does this everywhere mean: everywhere at the same time in an infinite unverse ?
IMO "you" should not try to explain something that is not clear by something that is also not clear.
This ubiquity (omnipresence red.) of the big bang holds no matter how big the universe is or even whether it is finite or infinite in size.
What is the difference between the concepts finite and infinite ?
The true question to answer is at the moment of the Big Bang was the universe than finite or infinite?
Observers living in the Andromeda galaxy and beyond have their own observable universes that are different from but overlap with ours. Andromedans can see galaxies we cannot, simply by virtue of being slightly closer to them, and vice versa.
This sentence is misleading. Generally speaking we observe the same large galaxies as the Andromedans but at a different time epoch.
The totality of space could be infinite
What means the totality of space? IMO a totality is by difinition finite.
Shrink an infinite space by an arbitrary amount, and it is still infinite
Infinite space (an infinite universe) can neither shrink or expand.
Receding Faster Than Light
See the text in the box: Can Galaxies Recede Faster Than Light?
v = Recession Velocity
Blue line = Speed of light
6| / .
5| / . c
3| /. c .
2| / c .
1|/c . .
1 2 3 4
In expanding space, recession velocity keeps increasing with distance. Beyond a certain distance, known as the
Hubble distance, it exceeds the speed of light.
Figure 1 demonstrates this situation. Figure 1 shows the situation at a certain moment t.
In Milne's Universe the size of the Universe increases linear in time.
Figure 2 shows how the size of the universe increases as a function of the time since the Big Bang.
In this particle case the expansion speed is two times the speed of light c.
The line cccc shows the size of the universe when the expansion speed is.
This line is important for the following reason:
See also Box 1 below.
- The events that happened between this line and the time axis are rather easy to observe.
- For the events that happened between the line R=2ct and the line R=ct this is rather more complicated because the expansion speed is larger than c.
Strectching and Cooling
In this paragraph we read:
For example, the microwave background radiation currently has a temperature of about three kelvins, whereas the process that released the radiation occurred at a temperature of about 3,000 kelvins.
How do you know this? What is important is what is actual measured. You can not measure a temperature directly . What you can measure are movements (frequencies) and you can interprete these movements as temperatures.
Running to Stay Still
In this paragraph we read:
the idea of seeing faster-than-light galaxies may sound mystical, but it is made possible by changes in the expansion rate. Imagine a light beam that is farther than the Hubble distance of 14 billion light-years and trying to travel in our direction.
The question to answer is what are the youngest galaxies we can observe at present in an expanding uniform universe.
But the Hubble distance is not fixed, be cause the Hubble constant, on which it depends, changes with
I do not think that the Hubble constant and Hubble distance are necessary to answer the above question.
Box 1 - Milne's Universe
- Consider an universe which expands with the speed of light. That means when the universe was 5 billion years old the size was 5 billion light-years. Consider a supernova at the edge of the universe which transmits light towards us. When will we see this?
- When there is no space expansion involved we will observe this light after 5 billion light years.
- With space expansion this picture changes because initially the distance of the photons travelled towards us and the distance caused by space expansion away from us will cancel. That means the distance will almost not change in absolute sense. But in relative sense (relatif to the edge) the distance will change. That means the expansion component away from us will decrease. The overall result will be that the speed of the photons towards us will increase. When the photons are close this will be the speed of light.
The overall result will be that we will observe the SN not 10 billion years after the Big Bang but more roughly 14 billion years after the BB.
- Consider an universe which expands with twice the speed of light. That means when the universe was 5 billion years old the size was 10 billion light years. Consider a supernova at the edge of the universe which transmits light towards us. When will we see this?
- When there is no space expansion involved we will observe this light after 10 billion light-years.
- With space expansion this picture changes specific compared with the first case. Initially the expansion speed away will be 2 times c and the speed towards us c. The net result will be an expansion speed of c away from us. This means that the photons will move away from the edge. The result is that the expansion speed caused by space expansion away will decrease. The net result will be that the expansion speed away will decrease until the expansion speed caused by space expansion and the speed towards us cancel. That is the maximum distance reached. After that the photons will start to approach us.
This type of universe or world model is called: Milne's model.
To observe more details select: Milne's model
For a general discussion about visaul horizons read this:
Visual horizons in World-Models Article by W.Rindler. 1956
However there is one more important point. Assume that the maximum distance in case 2 happened 5 billion light years after the BB. That means we will observe this roughly 14 after the BB. That inturn means that incase the universe expands with 2 times c the youngest galaxies we can observe are roughly 2 billion years old.
Now let us go back to page 43 (31).
If space were not expanding, the most distant object we could see would now be about 14 billion light-years away from us, the distance light could have traveled in the 14 billion years since the big bang.
This is a very confusing sentence because how do we know that this universe was created spontaneous 14 billion years ago.
All what we know for example is that when space expansion is c and when photons are not affected by space expansion, that when the age of the universe is 14 billion years the youngest galaxies we can observe are 7 billion years and that their present distance is 14 billion light years.
But because the universe is expanding, the space traversed by a photon expands behind it during the voyage. Consequently, the current distance to the most distant object we can see is about three times farther, or 46 billion light-years.
You get this number when you assume that space expansion is roughly 3 times c.
However and that is important we observe this distant object when it was very young. Maybe roughly 1 billion years of age.
The recent discovery that the rate of cosmic expansion is accelerating makes things even more interesting.
The issue is more that the cosmic expansion is not decelerating and is very close to a linear expansion rate.
In an accelerating universe, however, we are surrounded by a boundary beyond which occur events we will never see - a cosmic event horizon.
IMO there is big difference between the state of actual universe and the state of the universe that is observed. If we assume that the age of the universe is 14 b years and the age of our galaxy is 13 b years than we can assume that the universe is filled with galaxies of the same age.
My understanding is that we can observe all these galaxies but the father away they are the younger we will observe them.
Is Brooklyn Expanding?
When you compare the box
specific the pictures in the section RIGHT there seems to be a problem.
- WHAT KIND OF EXPLOSION WAS THE BIG BANG? at page 39 (27) with the box
- DO OBJECTS INSIDE THE UNIVERSE EXPAND, TOO? at page 45 (33),
This requires a good explanation. The text reads:
- In the box at page 39 the distance between the galaxies increases linear.
- In the box at page 45 the distance between the galaxies in the pictures 1,2 and 3 increases linear and in the pictures 3,4 and 5 stay the same.
Neighboring galaxies initially get pulled apart, but eventually their mutual gravity
overpowers expansion. A cluster forms. It settles down into an equilibrium size
IMO you can only discuss clusters if the combined gravitational force of the cluster is always larger than the supposed expansion force. That means globally the cluster will expand but locally the cluster will stay together. This is much easier to understand if the major galaxies of a cluster rotate among a more central point.
My prediction is that the Andromeda Galaxy and the Milky Way Galaxy will not merge.
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Created: 25 Februari 2014
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