Search found 180 matches

by ajb
Tue Jul 29, 2008 3:44 pm
Forum: Astrophysics
Topic: The twin's paradox...not the usual discussion
Replies: 77
Views: 34842

Speed of time? dt/d\tau for the proper time of an inertial observer \tau ?

You can't do this for photons. \tau does not have the interpretation as the photons proper time.

This all comes from confusing which frames are valid inertial frames and what are not.
by ajb
Tue Jul 29, 2008 8:24 am
Forum: Astrophysics
Topic: The twin's paradox...not the usual discussion
Replies: 77
Views: 34842

Light is massless, therefore doesn't suffer the effects of time dilation. You got me on that one....I am not sure whether mass is relevant to time dilation....will have to investigate. Remember that light (or any other massless particles) have no well defined rest frame. So you cannot talk about ti...
by ajb
Fri Jul 18, 2008 6:59 am
Forum: Astrophysics
Topic: Are we all traveling at Light Speed?
Replies: 20
Views: 11633

The expansion of the universes is really on a large scale. Local gravity can overcome this and so we do have gravitationally bound objects, such as a galaxy and local clusters of galaxies. Some of the objects in our own galaxy cluster are moving towards us and not away! The point here is that the ex...
by ajb
Fri Jul 11, 2008 9:54 am
Forum: Astrophysics
Topic: Are we all traveling at Light Speed?
Replies: 20
Views: 11633

No big_kev, keep the pen and draw a Minkowski diagram.

:P
by ajb
Thu Jul 10, 2008 4:42 pm
Forum: Astrophysics
Topic: Explaining the physics of a singularity
Replies: 35
Views: 14424

I don't follow what you mean by "temperature loop". (QFT at finite temperature is something else, basically t-> \tau= -it and then you make time periodic.)

Anyway, if you are serious about learning more about general relativity then you should read Wald's book.
by ajb
Thu Jul 10, 2008 2:27 pm
Forum: Astrophysics
Topic: Explaining the physics of a singularity
Replies: 35
Views: 14424

Honestly no one knows how to deal properly at "t=0". Quantum gravity effects must be important here. I know people out there do try to work in this realm using loop quantum gravity etc. I don't know any of the details of this. I am not a cosmologist. :wink: The usual way to deal with singu...
by ajb
Thu Jul 10, 2008 12:54 pm
Forum: Astrophysics
Topic: Explaining the physics of a singularity
Replies: 35
Views: 14424

Generally, if something is calculated to be infinite then your theory is in trouble. We can not measure infinities, therefore they are unphysical. As for your request, I don't really understand what you are asking for. Anything I can think of is not well defined at T = infinity. Well, thermodynamics...
by ajb
Thu Jul 10, 2008 12:06 pm
Forum: Astrophysics
Topic: Explaining the physics of a singularity
Replies: 35
Views: 14424

I am not sure I would say that the blackhole singularity has infinite temperature. Basically the degrees of freedom are removed. You have to be careful when comparing the big-bang singularity with the singularity found in a blackhole. Simply, the FRW* solution is not static and where the Schwartzchi...
by ajb
Thu Jul 10, 2008 11:34 am
Forum: Astrophysics
Topic: Spacetravel...I still don't get it.
Replies: 85
Views: 29876

To to clarify one point. Einstein did not predict at static universe. He knew that as he originally formulated it general relativity predicts that the universe is not static. It was the current thinking at the time (before Hubble's observations) that the universe was indeed static. This lead Einste...
by ajb
Thu Jul 10, 2008 10:38 am
Forum: Astrophysics
Topic: Spacetravel...I still don't get it.
Replies: 85
Views: 29876

To to clarify one point. Einstein did not predict at static universe. He knew that as he originally formulated it general relativity predicts that the universe is not static. It was the current thinking at the time (before Hubble's observations) that the universe was indeed static. This lead Einstei...
by ajb
Thu Jul 10, 2008 10:30 am
Forum: Astrophysics
Topic: Explaining the physics of a singularity
Replies: 35
Views: 14424

Hi all, Just to sort of clarify where I don't understand the expansion, the point in the finate time where the Universe has expanded and before the first atoms have formed, say for arguments sake 25,000 years along the time line, for me the Universe still seems to be the singularity we started with...
by ajb
Wed Jul 09, 2008 7:19 pm
Forum: Astrophysics
Topic: Explaining the physics of a singularity
Replies: 35
Views: 14424

why does the CBR not overtake the expansion rate? I apologise if it's only ajb you want an answer from. But his will probably be correct and more to the point. In Big Bang theory the expansion rate refers to an expansion everywhere in space in all directions . From any point in the universe space w...
by ajb
Wed Jul 09, 2008 4:28 pm
Forum: Astrophysics
Topic: Explaining the physics of a singularity
Replies: 35
Views: 14424

Relativity and quantum physics are most definitely wrong. Would you care to post your mathematical proof of that??? No, I thought not. How did I guess that would be the case? By wrong , I assume that big_kev means that if you apply a physical theory outside of the scales it is applicable to then yo...
by ajb
Tue Jul 08, 2008 9:54 pm
Forum: Astrophysics
Topic: Explaining the physics of a singularity
Replies: 35
Views: 14424

Yes, but what to they mean by "confirm"?

All they mean is that this model describes nature to a high degree of accuracy. What else could they mean?
by ajb
Tue Jul 08, 2008 9:44 pm
Forum: Astrophysics
Topic: Explaining the physics of a singularity
Replies: 35
Views: 14424

Rumour has it the "big bang" is still theoretical. As we are talking about theoretical physics that fine. All we can really do is investigate models and ask how they relate to nature. So, the big bang was and always will be theoretical. :-) But you should be aware of how accurate the big ...