What was around before the Big Bang?

tussock · Post by **tussock** » Sat Nov 07, 2009 8:21 am

Time is a byproduct of the big bang, there is no such concept as "before" it.

As to where matter came from, it's just energy that's stuck in a hole it can't normally climb out of. Energy came from the same place as space and time and forces and physical laws and fundamental constants and all the hidden dimensions and the dark matter and dark energy and whatever we haven't found yet, which is probably indistinguishable from nothing if you could put it all back together again, which you can't.

But that's all just how our brain sees it, which is just a trick of the evolution of brain circuitry to help us humans catch some more warm protein for dinner now and then, and thus build better brain circuits. God only knows what's really going on.

shadzar · Post by **shadzar** » Sat Nov 07, 2009 8:25 am

tussock wrote:evolution of brain ~~~God

Does not compute....

Did you set us this paradox of thought on purpose? Welcome.

Kaelik · Post by **Kaelik** » Sat Nov 07, 2009 7:33 pm

Since this thread has become about Dark Matter and energy.

They know a lot more about that stuff than people usually claim:

See this.

tussock · Post by **tussock** » Sun Nov 08, 2009 2:47 am

Pfft. God done built a 13 billion year old universe in seven days, 6000 years back, full of things that had been evolving for aeons, on any number of planets which naturally accumulated from the ruins of old, giant stars. It says so in the Bible, which God made people's brains develop out of ancient stories that He created the seeds for (which didn't come out terribly accurate, but that's free will for you).

Also, you're just dreaming this, and can't really prove otherwise.

Gelare · Post by **Gelare** » Sun Nov 08, 2009 4:20 am

Hey Kaelik, in that lecture, where he's talking about how the far away galaxies will accelerate to faster than c, and then we won't be able to see anything outside our own galaxy anymore, he's like, "General relativity says it's okay for stuff to go faster than c!" and I thought that was very much not the case. Illumination, plz?

virgil · Post by **virgil** » Sun Nov 08, 2009 4:38 am

He partially explained it in the lecture itself. In general relativity, every galaxy is stationary with respect to each other, while space itself expands between them. The distance is increasing to a rate greater than c, it's the relative velocity from each other's perspective that cannot exceed c; similar to how two rockets leaving Earth in opposite directions at .75c will separate from each other at a rate of 1.5c from a third party perspective.

shadzar · Post by **shadzar** » Sun Nov 08, 2009 4:55 am

tussock wrote:Pfft. God done built a 13 billion year old universe in seven days, 6000 years back, full of things that had been evolving for aeons, on any number of planets which naturally accumulated from the ruins of old, giant stars. It says so in the Bible, which God made people's brains develop out of ancient stories that He created the seeds for (which didn't come out terribly accurate, but that's free will for you).

Also, you're just dreaming this, and can't really prove otherwise.

If I am dreaming tgdmb.com then it must be a fever induced nightmare.

Gelare · Post by **Gelare** » Sun Nov 08, 2009 6:38 am

virgileso wrote:He partially explained it in the lecture itself. In general relativity, every galaxy is stationary with respect to each other, while space itself expands between them. The distance is increasing to a rate greater than c, it's the relative velocity from each other's perspective that cannot exceed c; similar to how two rockets leaving Earth in opposite directions at .75c will separate from each other at a rate of 1.5c from a third party perspective.

Okay....but we're on Earth doing the observations, right? So even if we're going that way <-- at .75c and the far off galaxies are going that way --> at .75c, relative to us the far off galaxies are only going away at a rate of, I forget my relativity calculations, but I think it's like .85c. So how do they go faster than c and drop out of view?

TarkisFlux · Post by **TarkisFlux** » Sun Nov 08, 2009 6:53 am

Gelare wrote:Hey Kaelik, in that lecture, where he's talking about how the far away galaxies will accelerate to faster than c, and then we won't be able to see anything outside our own galaxy anymore, he's like, "General relativity says it's okay for stuff to go faster than c!" and I thought that was very much not the case. Illumination, plz?

Well, c is the speed that light travels, and is the fastest that any matter or energy can travel. It's worth looking at it like a vector though, since like virgileso said, it doesn't really have any bearing on the relative speed of objects when measured by someone else. We have light leaving both sides of the planet every day and the distance between those photons grows at a rate of 2c. Neither of them is traveling faster than c and both are outside of the light cone of the other, so it's all totally fine. Even this isn't the whole picture though, since there are plenty of things in the universe that do move faster than c, they're just not things we can use and we just have to get into information theory a bit.

So, there's a corollary to general relativity and QM that says that information can't travel faster than the speed of light. Which leaves lots of other things that can and do travel faster though. In a sun / planet system, the speed that the planet's shadow sweeps across empty space is a function of the distance from the system, and that can exceed c really easily. It just doesn't matter because the information we get from the system is passed on by the light or lack of light and gets to us at c Even if we could tell something about the size of the object by the duration of the shadow, that info only came to us at speed c. The particles in an EPR paradox pass status changes at approx infinity speed because they're coupled and operating non-locally, but since we can't actually do anything with that information or use the setup in a creative way to pass information it doesn't matter how fast they do it.

Edit:

Gelare wrote:
virgileso wrote:He partially explained it in the lecture itself. In general relativity, every galaxy is stationary with respect to each other, while space itself expands between them. The distance is increasing to a rate greater than c, it's the relative velocity from each other's perspective that cannot exceed c; similar to how two rockets leaving Earth in opposite directions at .75c will separate from each other at a rate of 1.5c from a third party perspective.
Okay....but we're on Earth doing the observations, right? So even if we're going that way <-- at .75c and the far off galaxies are going that way --> at .75c, relative to us the far off galaxies are only going away at a rate of, I forget my relativity calculations, but I think it's like .85c. So how do they go faster than c and drop out of view?

virgileso's explanation above was just a point about how if you have 2 objects going away from each other the distance between them, as measured by a 3rd party, is just the sum of their speeds. If you are one of the two parties, things are different as you suggest. There's a clearer way to put it though.

If space expands at a rate of 1.1 lightyears / year between galaxies and light only travels 1 lightyear per year, that light will never reach us. It can't make up the extra distance, ever. And since no information is being passed by that extra space, just lost in it, it's totally legit (if annoying). Which is what they tell us is happening to galaxies. There is just more extra space between them that is basically coming from nothing than the light can deal with.

Gelare · Post by **Gelare** » Sun Nov 08, 2009 7:07 pm

TarkisFlux wrote:There is just more extra space between them that is basically coming from nothing than the light can deal with.

Wild. Thanks.

Crissa · Post by **Crissa** » Sun Nov 08, 2009 10:44 pm

I would note that the space that gets added gets added in every position equally, so that would mean the distance isn't all added in front of the photon, but at all positions along its path.

So things from further and further away would continue to redshift until the length of their spectra is wider than the distance.

-Crissa

tussock · Post by **tussock** » Sun Nov 08, 2009 11:45 pm

TarkisFlux wrote:If space expands at a rate of 1.1 lightyears / year between galaxies and light only travels 1 lightyear per year, that light will never reach us. It can't make up the extra distance, ever.

This bit is incorrect. See, the space halfway between the galaxies is only travelling at 0.55c wrt either (or whatever, I forget), so light can get to the midpoint, and can get from the midpoint across the rest.
The light effectively "accelerates" as the space it progresses through is moving ever slower compared to the destination.

You can stop light getting from A to B through open space, but it involves constant acceleration of the source or destination at a greater rate than the light can "accelerate" relative to the other. Inflation will get there relative to the CMB only long after the heat death of all local galaxies, so it's not really a problem.

Oh, black holes do it all the time, of course, but they're possibly just throwing all that information into the distant future as they evaporate, it's hard to know.

CatharzGodfoot · Post by **CatharzGodfoot** » Sun Nov 08, 2009 11:48 pm

TarkisFlux wrote: In a sun / planet system, the speed that the planet's shadow sweeps across empty space is a function of the distance from the system, and that can exceed c really easily. It just doesn't matter because the information we get from the system is passed on by the light or lack of light and gets to us at c Even if we could tell something about the size of the object by the duration of the shadow, that info only came to us at speed c.

The speed of the 'shadow' can't exceed C, because there is literally no shadow until the last of the light that was in that empty space reaches you (at the speed of light).

virgil · Post by **virgil** » Mon Nov 09, 2009 12:23 am

The shadow can indeed exceed light speed. If I have a candle and a sufficiently distant wall, I can move a pencil in front of the candle. After the time for the light to travel to the wall and back for me to perceive its effects, it will include the shadow of a pencil crossing the full width of the wall in the same time it took me to move it in front of the candle flame. From my perspective, the 'shadow' did indeed cross the length at a speed greater than c.

TarkisFlux · Post by **TarkisFlux** » Mon Nov 09, 2009 2:56 am

tussock wrote:
TarkisFlux wrote:If space expands at a rate of 1.1 lightyears / year between galaxies and light only travels 1 lightyear per year, that light will never reach us. It can't make up the extra distance, ever.
This bit is incorrect. See, the space halfway between the galaxies is only travelling at 0.55c wrt either (or whatever, I forget), so light can get to the midpoint, and can get from the midpoint across the rest.
The light effectively "accelerates" as the space it progresses through is moving ever slower compared to the destination.

/shrug

That bit was a bit outside my classes, so I was just going off of what I understood from the above posts. I didn't get the impression that the space was moving, just that it was inflating and so there was more there to traverse after the light started moving than there was before. Still,

Edit: Just noticed this was cut off. I have no idea where I was going with that. So... yeah.

shadzar · Post by **shadzar** » Mon Nov 09, 2009 3:17 am

The big bleaagh

tussock · Post by **tussock** » Mon Nov 09, 2009 9:56 am

TarkisFlux wrote:
tussock wrote:
TarkisFlux wrote:If space expands at a rate of 1.1 lightyears / year between galaxies and light only travels 1 lightyear per year, that light will never reach us. It can't make up the extra distance, ever.
This bit is incorrect. See, the space halfway between the galaxies is only travelling at 0.55c wrt either (or whatever, I forget), so light can get to the midpoint, and can get from the midpoint across the rest.
The light effectively "accelerates" as the space it progresses through is moving ever slower compared to the destination.
/shrug

That bit was a bit outside my classes, so I was just going off of what I understood from the above posts. I didn't get the impression that the space was moving, just that it was inflating and so there was more there to traverse after the light started moving than there was before. Still,

Well, yes, space is interesting like that. If you inflate some length of space by 10% every few billion years, the bits at either end will be both moving with respect to each other (a change in distance over time) and accelerating that movement (10% of 10 LY in the first few billion, 10% of 11 LY in the next, and so on), despite not moving within their own little segment of space.

So we say the space is moving relative to that distant space, and accelerating, to make it clear the galaxies are not accelerating or moving in their local space.

It's the growth of that acceleration which will eventually outrun light (assuming all sorts of weird things to be true).

Edit: Just noticed this was cut off. I have no idea where I was going with that. So... yeah.

I've patented that trick, so you'll have to

Username17 · Post by **Username17** » Mon Nov 09, 2009 1:16 pm

Light crossing an expanding region is a compound interest problem. As long as each meter of the distance is not doubling in the time it takes for the light to cross it, then the light is going to be making forward progress relative to the original distance even if the total distance is growing faster than that. As time goes by, more and more of the total distance is "behind" the photon and less and less (percentage wise) is "in front." So it generally speaking gets there eventually. The problem is that this process redshifts things more and more the longer it's allowed to go on. So while eventually I think it might get to the point where in an Achilles vs. Turtle fashion it takes an infinite amount of time for the photon to arrive, in a much more manageable and fathomable timescale it will get to the point that by the time the photon arrives it will be so low energy that it cannot be detected. First it will fall off the visible spectrum, and then it will fall off the detectable spectrum.

So indeed, there will come a time when the sharpest minds of the universe do flawless observation and come to the reasoned conclusion that their galaxy is alone and static - surrounded on all sides by an endless black void that emits no light and imparts no pull. Because the other galaxies will be being flung away from them so fast that there is no light from them that can be detected.

-Username17

tzor · Post by **tzor** » Mon Nov 09, 2009 2:54 pm

Gelare wrote:... he's like, "General relativity says it's okay for stuff to go faster than c!" and I thought that was very much not the case. Illumination, plz?

This is going to get complex; first of all some “general” relativity nit picking.

Specific relativity involves fixed velocities and does not take acceleration into account. The relativity part is that it is impossible to know which object is moving and which is not. (Note: The twin’s paradox is not a paradox but since it involves acceleration it is a problem for general relativity not specific relativity.)

General relativity involves acceleration. The relativity part is that gravitational forces cannot be distinguished from acceleration forces.

Under general relativity, the inertial mass of an object increases as the velocity increases. Thus it would take infinite energy to accelerate an object to C. There is one known exception to this rule and one exception in theory.

The known exception is when the object has no inertial mass to begin with. Bosons such as photons fall under this category and thus travel at exactly C.

The exception in theory is when a particle always travels faster than the speed of light, in which case it can go no slower than the speed of light. The theoretical particle the tachyon is considered to unstable to exist. The inertial mass of such a particle is imaginary.

The biggest problem with faster than light is: under the right relativistic frame a faster than light particle can be seen as going backwards in time. This causes all sorts of problems in terms of cause and effect. (Just explore your standard science fiction stories on time travel.) As a result it is often avoided like the plague.

In modern physics, the notion of causality had to be clarified. The insights of the theory of special relativity confirmed the assumption of causality, but they made the meaning of the word "simultaneous" observer-dependent. Consequently, the relativistic principle of causality says that the cause must precede its effect according to all inertial observers. This is equivalent to the statement that the cause and its effect are separated by a timelike interval, and the effect belongs to the future of its cause. Special relativity has shown that it is not only impossible to influence the past, it is also impossible to influence distant objects with signals that travel faster than the speed of light.

In the theory of general relativity, the concept of causality is generalized in the most straightforward way: the effect must belong to the future light cone of its cause, even if the spacetime is curved. New subtleties must be taken into account when we investigate causality in quantum mechanics and relativistic quantum field theory in particular. In quantum field theory, causality is closely related to the principle of locality. A careful analysis of the phenomena is needed, and the exact outcome depends on the interpretation of quantum mechanics chosen: this is especially the case of the experiments involving quantum entanglement that require Bell's Theorem for their implications to be fully understood.

Off of the top of my head I can’t recall if Hawking addressed causality in his space time model of the universe.

Kaelik · Post by **Kaelik** » Mon Nov 09, 2009 7:48 pm

While most of it has been covered. One thing that hasn't yet been mentioned about living in an empty universe is that:

Light intensity is a factor of distance.

So in fact, if the distance between us and Andromeda doubles, the actual intensity of light from Andromeda decreases.

So there is a practical limit even if the space between didn't ever grow faster than the speed of light (it will eventually, but even if it didn't) it's that when only one photon from the entire Andromeda galaxy reaches us every hour, it's going to be difficult to piece that information into an actual galaxy, when compared against random reflections and emissions within our own galaxy.

Light intensity actually won't even be that low until after everything has been red shifted to non existence, but hypothetically, even without the expansion distance being greater than speed of light, it would still become basically just a cosmic background more than anything sensible.