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Cesiumsponge

Sun Jul 02 2006, 07:05PM

Registered Member #397 Joined: Wed Apr 19 2006, 12:56AM
Location: Western Washington
Posts: 125

EastVoltResearch wrote ...

Ah, so if nothing can travel faster than light, how do you explain the big bang. The universe went from practically a singularity to an entire universe in under a microsecond.

You are referring to the cosmic inflation where the universe expanded 10^50 in volume in 10^-32 seconds. Prediction models of Grand Unified Theory states that electromagnetism and the electrostrong/weak forces can be combined further into a "superforce" that would only exist under extreme energy levels of 10^15 GeV and temperatures of 10^28K+.

Obviously at those incredible densities and temperatures present at the birth of the universe (in which basic subatomic struture didn't even exist ), the speed of light by way of thought experiment would be much slower than the constant we commonly use with respect to a pure vacuum today because it took place 10^-35s after the Big Bang. It is, afterall, travelling through a mind-boggling dense medium.

That is not hospitable environment. Heck, the universe was even completely opaque to electromagnetic radiation for a long span of time. We can only check background microwave radiation back to the point where the universe was approximately 1500 times smaller than it is today, and several hundred thousand years old after the epoch of decoupling allowed the transmission of electromagnetic radiation. The universe is still expanding and the inflationary epoch did not bring the universe anywhere near it's current size as it stands today.

Describing the actual mechanics and physics (as we understand them with current knowledge) involves fun exotic stuff like high-energy false vacuums and oddball things I do not pretend to be an expert at but it was briefly covered in basic 100 and 200 level astronomy courses, and likely described in detail at higher levels. I am not sure if theories have changed since the last four years as astronomy theory and knowledge seems to change with more regularity than other branches of science.

IamSmooth

Mon Jul 03 2006, 10:10PM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567

Since the relativity and the universe topic seems to be getting older, like the universe, here is another relativity thought topic:

In the twin paradox the returning twin is much younger than the one stationary on earth. Part of the explaination is that the returning twin changes direction; why else couldn't the twin on earth be younger instead? My question is happens if the twin in the spacecraft did not return home, but landed on the planet after getting there at close-to-light speed? That is, is he younger than the twin at home if there is no change in direction, or is his acceleration and deceleration sufficient to satisify the paradox?

Desmogod

Tue Jul 04 2006, 01:09AM

Registered Member #139 Joined: Sat Feb 11 2006, 11:01AM
Location: Perth, Western Australia
Posts: 358

IamSmooth wrote ...

That is, is he younger than the twin at home if there is no change in direction, or is his acceleration and deceleration sufficient to satisify the paradox?

Change in direction has no bearing on the twins paradox.
The closer Twin 1 gets to the speed of light, then the slower time runs for him in relation to a fixed observer, Twin 2.
If twin 1 changes direction, and flies back towards twin2 at close to the speed of light, then this will just increase the disparity in age difference, it is not a neccesity for the paradox to function.

Bored Chemist

Tue Jul 04 2006, 04:47PM

Registered Member #193 Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022

"I personally believe that everything in the universe is made out of sub-dimensional wavelengths/waveshapes"
What on earth does that mean?
I can't help thinking that "sub dimensional" sounds like it's straight out of a sci-fi film script.
BTW, the twins paradox isn't a paradox at all. One (and only one) twin experiences the acceleration as his ship takes off.
Velocity might be relative, but acceleration isn't (or rather it might not always be)

Marko

Tue Jul 04 2006, 04:55PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Paradox doesn't need to be a bunch of mutually contradictive statements, event that counters intuition (wich would imply that time is a constant) is also sometims called a paradox, even if it is actually an very real physical phenomena.

Desmogod

Wed Jul 05 2006, 01:31AM

Registered Member #139 Joined: Sat Feb 11 2006, 11:01AM
Location: Perth, Western Australia
Posts: 358

Bored Chemist wrote ...

BTW, the twins paradox isn't a paradox at all. One (and only one) twin experiences the acceleration as his ship takes off.
Velocity might be relative, but acceleration isn't (or rather it might not always be)

The twins paradox is only called such because at the time of relativity, everyone had a different view on time, i.e. that it was constant. It seems pretty common sense to us now that time is relative, But explaining this to someone around the time that Einstein postulated it would have blown their mind. So it remains the Twins Paradox, if only in nomenclature.

Simon

Wed Jul 05 2006, 01:57AM

Registered Member #32 Joined: Sat Feb 04 2006, 08:58AM
Location: Australia
Posts: 549

Desmogod wrote ...

Change in direction has no bearing on the twins paradox.
The closer Twin 1 gets to the speed of light, then the slower time runs for him in relation to a fixed observer, Twin 2.
If twin 1 changes direction, and flies back towards twin2 at close to the speed of light, then this will just increase the disparity in age difference, it is not a neccesity for the paradox to function.

Change in direction does have a place, at least in the usual formulation of the twins paradox.

Remember that velocity is relative and there is no absolute reference point in space. So how can you say that it is twin 1 who nears the speed of light and not twin 2? This question forms a true, formal paradox since despite this fact, you can definitely say that time "slows down" for twin 1.

The answer is that special relativity doesn't apply to the twins paradox as it is formulated here. Taking off from Earth and coming back again involves either a) acceleration or b) curved space time. In either case, we're entering the realm of general relativity.

While inertial reference frames are perfectly relative, acceleration is not.

Ben

Wed Jul 05 2006, 03:26PM

Vigilatny
Registered Member #17 Joined: Thu Feb 02 2006, 02:47PM
Location: NL
Posts: 158

Nothing can travel through spacetime faster than c. Spacetime itself, aparently, has no such restrictions.

EastVoltResearch wrote ...

So again, I ask, if a similar process took place, hypothetically of course, and the space expanded by a factor of 2 (i.e. doubled in size) overnight, is there anyway you could tell it had occurred ? ? ?

Depends on the scale(how long would it take for the information relating such changes to propagate), on the whole the universe would get colder.

Also pseudoscience is strictly forbidden.

Bored Chemist

Wed Jul 05 2006, 05:16PM

Registered Member #193 Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022

"Remember that velocity is relative and there is no absolute reference point in space. So how can you say that it is twin 1 who nears the speed of light and not twin 2?"
Because he is the one who gets pushed back in his seat by the rocket's acceleration. The 2 twins undergo different experiences and these different experiences have different outcomes. Where's the paradox?
Granted that you don't (from common experience) expect time dilation and that therefore the different rates of aging are unexpected. That's not what the "paradox" is about.
Given that all motion is relative you can't say which twin stayed still. from that point of view a skeptic might say "How come it's the correct twin that ages; you can't say which one moved?" With no acceleration that would be a true paradox. On the other hand only one of them actually gets in the rocket and gets accelerated- that's why his time "slows down" compared to the other.

Bjørn

Wed Jul 05 2006, 05:52PM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

So what if you put twin 2 in a centrifuge with the same acceleration but with a fraction of the speed?

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