Examining Big Bang Location and Visible Object Density in the Night Sky

[DaveC426913]

In response I get something about the universe being a balloon.

You're faulting us because you're having trouble grasping these concepts? Reading a book on the subject will give you a basis upon which to ask more well-formed questions. Either that, or accept that these questions are too complex to be fully answered in a forum.

 

[the_viewer]

In classical mechanics you can use an euclidean space $$\mathbb{E}^3$$ for modelling the world. You choose an origin for your coordinates, let's say $$P_0$$, and an euclidean basis, that is, three linear independant vectors $$\left(e_1,e_2,e_3\right)$$. Then you can reach every point (assigned with a vector $$\vec{v}$$ pointing on it) in your room with a linear combination of these three vectors:
$$\vec{v}=x\cdot e_1 + y\cdot e_2 + z\cdot e_3$$
Now x is the displacement in direction of $$e_1$$ and so on...
This is how the coordinates x,y and z can be defined in an euclidean space.
Same for the time: You specify an origin in time, let's say $$t_0$$ and then t is the distance in time to this origin (measured with a clock).

When you switch to relativity now, you will encounter that the coordinate in time is not independent from the coordinates in space. (You cannot travel faster then light, so when traveling to Hawaii, you need at least a specific time to reach your destination. So: time and space have something to do with each other.)
Then you define things like Minkowski-Spaces and other things to do elegant math with the above defined numbers (x,y,z,t).

So far for missing definitions...

 

[cristo]

The speed of light.

The speed of light is constant.

By definition, distance and time are such as to make the speed of light constant.

Ergo, the speed of light is constant.

If you wish to discuss other issues, then please start another thread in the appropriate forum (s&gr)

In response I get something about the universe being a balloon.

The balloon analogy is exactly that: an analogy which was thought up to help explain concepts. The balloon analogy shows how a finite universe can be unbounded. The surface of the balloon is analogous with space, and an object "living" on the surface is analogous with us living in the universe. If you are sat on the surface of the balloon, you see that the "universe" is finite, since if you walk in one direction you will end up where you started, but yet it is unbound. If the balloon is inflating, then this is analogous to the universe expanding. Again, if we were sat on the surface of the balloon, we would see our "universe" expanding, but that there is no centre of the expansion: i.e. there is no "centre of the big bang."

Now, let's keep the discussion on this topic only. Any further posts on different matters will be deleted.

 

[hartlw]

Hartlw,

I really don't understand what you're complaining about. It obviously isn't possible to teach GR from scratch in every thread that has something to do with GR. The definitions you seek are available in any GR book. If you want a definition of some specific thing, then we can probably help you out.

Every physics book I have ever seen begins with a definition of the subject.

Force and mass, distance, time, electrical charge etc. All these definitions are intelligible without knowledge of the subject.

It's like saying you can't understand charge without Maxwells equations.

You make it sound like anybody who doesn't understand General Relativity is not a physicist and doesn't belong in physics, or this forum.

Why can't I ask for a definition of the objects dealt with by General Relativity without understanding general relativity?

As a reminder of where this thread started, I asked a simple question about the visible universe and I was told the universe was like a balloon. If nothing can be discussed without knowledge of general relativity, I'd say physics was dead. Or else general relativity winds up in the dust bin of esoteric physics "theories."

 

[DaveC426913]

As a reminder of where this thread started, I asked a simple question about the visible universe and I was told the universe was like a balloon. If nothing can be discussed without knowledge of general relativity, I'd say physics was dead. Or else general relativity winds up in the dust bin of esoteric physics "theories."

It sounds like you're expecting that the nature of the universe is a "simple question" and should be explainable to a layperson, without reference to mathematics. I'd say that's unrealistic and naive.

Have you read anything about Quantum Mechanics? It's going to blow your mind.

 

[hartlw]

It sounds like you're expecting that the nature of the universe is a "simple question" and should be explainable to a layperson, without reference to mathematics. I'd say that's unrealistic and naive.

Have you read anything about Quantum Mechanics? It's going to blow your mind.

I didn't ask for an explanation of the universe. If a particular theory requires mathematics, fine. I was just asking about the ingredients that go into the theory, a not unreasonable request.

I did briefly start Dirac in my youth, very very briefly. I am content with the explanation that energy levels of electrons in atoms are discrete, as are other phenomena on an atomic scale. As I recall, quantum mechanics is very specific as to what it is talking about, though the math may be complex. Also, as it limits itself to phenomena on an atomic scale, I can understand that there is no reason that the laws of macro physics should apply on the atomic level, and if you can come up with a mathematical, interpretable, explanation, fine.

According to classical E&M, an orbiting electron would lose energy by radiation and collapse into the nucleus. So you postulate fixed orbits. Makes sense to me even though I can't manipulate the wave equation.

Yet, results are expressed in understandable physical terms, like electronic orbits, energy levels, and the probability of an object (electron) being somewhere at a particular time in its orbit. SPACE and TIME are involved with a clear agreement about their meaning.
Also, you can't measure something without interfering with it. There is obviously a lot of intense physical thought being applied there.

Now let's apply the general theory of relativity, where the objects of the theory remain undefined until you understand the theory. Space and trime are not what you think they are. I am reminded of the ads for software that never give you the price until you virtually have bought it. Buy it, then we'll tell you the price.

I feel sorry for the people in quantum mechanics if the general relativity people ever get their foot in the door. Scratch one scientific discipline.

 

[Fredrik]

Looks like you're trying to get banned from the forum. I don't see the point, but you can of course do what you want (for a while).

The balloon analogy is actually very good, and so is the infinite plane analogy that I used in #11. The only way to understand why they are good analogies is unfortunately to study general relativity. If you're not going to do that, you're just going to have to take our word for it.

You whine about a lack of definitions, but you didn't specify what you felt wasn't sufficiently defined. You mentioned the speed of light, but I agree that that question belongs in a new thread in the relativity forum or in the philosophy forum. That question and its answer has a lot more to do with what a theory is than with the details of relativity. Edit: I have answered your question about the speed of light in the relativity forum.

 

[cristo]

This thread is no longer on topic, hence it will now be locked.

 

[Mentz114]

Hartlw:
In all your ramblings you ignore a very important thing - the theory you are rubbishing explains observed astronomical and astrophysical data better than any other. If that's not a connection with the real world give me a better one.( No, don't bother.)

What's wrong with you ? Were you frightened as a child by a relativist with a long beard muttering "g mu nu g mu nu .." under his breath ?