I may just be a neophyte here, but everyone seems to be applying rules of the universe to something that actually occured OUTSIDE the universe. We are scratching at what the rules are within the universe, who knows how everyhting works outside of it. Take the example of a large body of liquid suspended in zero gravity. Within that sphere of liquid, even though there is no gravity, the laws of friction will still apply which means objects within it will move slower. Outside that sphere of liquid, no such restriction applies. I know it oversimplifies, but I’d like to know what you think
But getting back to the Original Post. The universe can expand faster than light. Stars far enough from us are moving away at faster than the speed of light, but they are not moving faster than light locally to them.
For my own edification, is the reason that the speed of light is the “universal speed limit” is that it would take an infinite force to accelerate a mass to c? I got Newton’s F=ma in the two semesters of physics I needed to graduate. I vaguely remember a “relativistic” version of this equation. Something like force= blah blah in the numerator, but c-velocity in the denominator. c-c would give an infinite number and, therefore an infinite force would be required to accelerate a mass to c. Am I remembering this correctly? Since you can’t have an infinite force, you can’t have a velocity of c. Also, as I understand it, mass approaches infinity as v approaches c (I think that’s right).
Like I said, where’s a damn physics book when you need it. Clarification from the physics phynatics would be appreciated.
Dr. Matrix: Yeah, but when you’re talking about the universe at the size of 10E-34 metres it doesn’t really matter either way whether or not it could classicly move faster than light. Just by the uncertainty principle you’ll have lots of the universe going faster than light and jumping around randomly. Unless of course Planck’s constant was different back then.
I dunno, but it seems like there’s a lot of theorizing going on about something we know very little about. Was c different, was h different, how many dimension etc, etc…
Either way, all I’m saying is that even if you don’t assume space can move faster than light because it’s not ‘real’ you can still have an expansion faster than light. In fact, at that scale, you almost certainly will have lots of things going faster than light.
647, you’re right, the mass of an object increases as it approaches the speed of light. It also gets smaller. If an object did reach the speed of light, it would be infinitely massive and infinitely small. It would disappear from our universe. It would be a black hole, though a black hole is normally formed by the collapse of a super-massive star. Once its radius drops below a certain limit,(Schwartzchild radius?) its gravitational force becomes so strong (strength of gravity depends upon both radius and density), escape velocity is greater than the speed of light. No light can escape, it’s black and everything falls down into it.
Those who do not learn from the past are condemned to relive it. Georges Santayana
I’d still like to know if I got the c speed limit right, but as a physics layman, what’s the deal with relativity and quatuum mechanics both being experimentally correct but mutually exclusive (or something like that)? Not my area of expertise, but I’m under the impression that they (GR and QM) conflict with each other (at least with regard to experimental data).
Quasars have beenmeasured to travel at 94% speed of light. This recording was taken approx. 16.8 billion years ago. We know this because it is 16.8 billion light years away, and if originally travelling at velocity just a fraction off of the speed of light, it would still decelerate. So if quasars define the furthest reach of the visible universe, we can safely assume that the universe as we know it is 16,800,000,000,000 x Speed of light (km) long.
However, if the age of the universe minus 16.8 billion years is the time taken for a quasar to decelerate from practically the speed of light to 94% the speed of light then we could also assume that its rate of negative acceleration is constant due to the lack of friction, and possibly even the state of zero mass assumed by quasars. So, if the universe were expanding at the speed of light it would reach zero density instantaneously. If this occurred there would be approximately 7EXP-3600 kgs of matter to every cubic metre of the universe. At this point the stars would be under compression caused by the shift in viable expanse caused by their vast energy. Every star would become a black hole, and would eventually turn the remaining universe into a large gravity well - a physical impossibility, as energy can neither be created and destroyed unless this situation occurs.
So in conclusion, if the universe were expanding at the speed of light, the gravity and inertia caused by the infinitely undefinable energy needed would make it impossible for light to exist within the possible form of the universe, if it has a form.
To discuss check topic asking what shape is the universe - - Claymore J
Earlier DW3 said that some bright spark named John Movvat theorized that the speed of light has changed since the Big Bang. The speed of light is constant by definition.
The second is defined by be the time it takes for an atom of some particular element (I forget which one) to vibrate 1.79 bazilion times. The speed of light is defined as one light sec per sec. A light second is defined as the distance light travels in one sec. A meter is defined as some fraction of a light second.
The speed of light cannot change. It is a matter of definition.
Relativity says you can’t simply add “we’re moving away from object X at the speed of light” to “they’re moving away from object X at the speed of light in the opposite direction” and get “they’re moving away from us at twice the speed of light.” To X, this is apparently true, but to us (and them) we’re receding from each other at the speed of light.
If you meant something else, do you have a citation for it and could you clarify?
It’s not possible for material objects to move faster than (or as fast as, though you could in theory get arbitrarily close) the speed of light in a vacuum, which is the c in the relativity equations.
However, it’s definitely possible for material objects to move faster than the speed of light in a medium, such as water. I’ve seen this; it’s what produces that odd blue glow around the core of a pool-type reactor.
And immaterial objects can move more quickly than c. The usual example involves some kind of huge scissors-like structure in which the point where the upper blade crosses the lower blade moves faster than c when the blades are closed… this is okay, because it’s an imaginary geometrical construct and not an actual object (the scissor blades themselves, being material objects, are limited to c).
Don’t forget that space is a geometrical construct of matter and energy. Matter and energy creates space. There is no law (yet) which says space can’t be created in three dimensions at a velocity faster than light.
And expansion (or contraction) of the universe is related to gravity, so, it might be gravity which is not the universal constant it seems to be.
And to throw out a whimsical WAG with absolutely no science or mathematics to back me up: If all those early big-bangish particles were moving at near c speeds, then they had a very high relativistic mass which may be the cause for the ftl creation of space.
Hubble’s law V = H*r gives the velocity V of an object at a distance of r. If we set V>c, then we find that at distances greater than c/H the velocity would be greater than c. Of course at r = c/H there would be some sort of event horizon preventing us from receiving any information about what’s beyond.
What you’ve basically said is “If we assume that V can be greater than c, then we can find the conditions under which V is greater than c,” and I agree with that. My question was whether it would be valid to make that assumption in the first place.
torq
I was trying to find the distance where V was greater than c.
If you want to go the other direction: What would the recession velocity be for objects whose distance is greater than c/H? Phrased this way I am not assuming V>c. I am only assuming there is no upper limit on distance.
DrMatrix, pointing out that an object would become infinitely small and infinitely massive at c implies that said object cannot achieve c. I simply didn’t think that needed to be said. I hope no one thinks it’s possible to reach infinity.
Those who do not learn from the past are condemned to relive it. Georges Santayana
Another theory is that the universe is encased in dark matter expanding at the speed of light. The edge of the universe is a layer of photons forming a layer of pure energy expanding a fraction off of the speed of light, as it is not as far away as the ‘Dark Matter’. This would also explain why it was expanding but I don’t have time to go into that.
If the edge of the universe were not travelling at quite the speed of light it would also be decelerating. Suggesting that Black Holes and White Holes are areas that are travelling at the same speed as the dark matter and have not decelerated, so they have stretched with the dark casing and have intercepted the photon barrier.
Thus explaining why they cannot be seen.
Clarification from the physics phynatics would be appreciated.