# Big Bang Theory

1. Apr 8, 2010

### stevenbhester

If it was an infitesimally small point, then the composition of said infitesimal point would be dimensionless, and by definition without part. How could something without part erupt? I understand that an infitesimal point could form a substance if there is an infinite amount (in fact, any amount) But how it could make amtter composed of a finite amount of parts is illogical to me.

2. Apr 9, 2010

### ZapperZ

Staff Emeritus
Do you have the same complaint with electrons, quarks, etc. as well? After all, within the Standard Model, those are considered as point particles. Yet, we have seen them collide and produced a gazillion mess of other "substance". An electron in a condensed matter system (i.e. the materials you use) can, by itself, cause a whole lot of other higher-order virtual interactions.

Zz.

3. Apr 9, 2010

### bapowell

Nobody says that this is what happened. The current Big Bang theory does not address what banged, how it banged, why it banged, etc. Physicists have long believed that there is a physical problem with the singularity you are describing. The Big Bang theory is the cosmological model for describing the emergence of the universe out of a hot, dense, early state, and nothing more. At this task it has proven fantastically successful.

4. Apr 22, 2010

### rajkaj123

I agree with you. If a point has no part than, according to me, there is no way it can erupt. Also in mathematics the definition of a point says that it only has location

5. Apr 22, 2010

### Chimps

The laws of physics break down when you try to apply them to a singularity, so it is not relevant to the big bang theory, which is only concerned with non-point things. If you go back that far there is no theory.

6. Apr 24, 2010

### map19

You could use a similar argument for the production of particle pairs out of the vacuum.
But it happens.

7. Apr 25, 2010

### bapowell

Wait...what do singularities and particle pair production have to do with each other?

8. Apr 25, 2010

### map19

The argument seems to be that a thing without a 'part' can not 'erupt' out of nothing.
Also dragging in the red herring that "mathematics says". What happens in mathematics may or may not happen in the real world.
Particle pairs can and do appear out of nothing, provided enough energy is available, or is borrowed from the vacuum.
This may or may not be similar to the appearance out of nothing but energy of the big bang matter.
was the big bang a singularity ? depends on your definition.
Was it a hugely powerful single string. Are singularities strings ? - who knows.

9. Apr 25, 2010

### bapowell

The big bang singularity does not depend on 'your definition'. It is a mathematical artifact of the fact that when you take the $$t \rightarrow 0$$ limit of the Friedmann universe, you reach zero scale in finite time. No practicing physicist attributes any physical reality to this singularity. Ditto for the Schwarzschild singularity. A singularity is by definition 0-dimensional, so I don't see the connection to strings. The production of particles from the vacuum is an entirely different phenomenon. Particles that fluctuate out of the vacuum in flat space always return to the vacuum by virtue of the Heisenberg principle. This is a well-defined mathematically and is physically consistent (and even experimentally confirmed in certain cases). So, I disagree with this connection. I think we are getting astray from the OP's question, which I think has been satisfactorily answered -- it's meaningless to argue about singularities -- they don't exist. Attempting to make contact with pair production serves only to confuse this thread.

10. May 3, 2010

### cristo

Staff Emeritus
Nobody is saying that "something" erupted from "nothing". The term "big bang theory" is synonymous with saying that the universe was once a lot hotter and denser than it is today and it has expanded from that previous state. Thinking of things the other way around is not correct.

Exactly, and it is simply the mathematics of tracking the evolution of the universe back in time that produces this singularity at an initial time. However, this singularity is really just taken to show us that our model breaks down at that point.

As for your analogy with particle pair production, I'm at a loss as to how that is relevant.

11. May 3, 2010

### prakash kumar

what you're saying isn't false but not fully true. That point contains infinite amount of energy and the density of that point is also infinite. this is the answer of your problem with the view of classical physics or by relativity which predict singularities.
However in quantum physics no absurdes like singularities accur. It said that there may be quantum fluctuations. you must have to wait for "quantum theory of gravity" for a correct solution of your problem.

12. May 3, 2010

### Null_

From what I understand, when two particles collide or combine, all they have to do is "balance." A photon had a mass of 0, lepton # 0, and baryon #0. (0,0,0) When two photons collide (0,0,0) + (0,0,0) they can make any particles that equal this, for example (0,-1, 1) and (0,1,-1).

Now I'm not sure if this answers your question at all, but it hopefully helps you understand how something is created from seemingly nothing. I remember this from Asimov's "Science, Numbers, and I," which I highly suggest reading if you're like me and don't have much of a physics background yet.