Time and the expansion of the Universe

Hi All,

Has anyone contemplated that as the speed of the expansion of the universe is increasing, what happens when the expansion speed equals that of the speed of light

I have heard that the speed of light is actually slowing down and other rumors that time it's self is speeding up...

Time is directly linked to light speed so would the expansion of space not be an explanation of Time itself?

Just a thought.

I would be very interested to hear other thoughts on this matter.

All the best people...

Tim_UK74

I recommend Arxiv astro-ph/0310808: Expanding Confusion: common misconceptions of cosmological horizons and the superluminal expansion of the Universe. It says about superluminally (faster than the speed of light) receding objects:

In the LambdaCDM concordance model all objects with redshift greater than z ~ 1.46 are receding faster than the speed of light. This does not contradict SR because the motion is not in any observer�s inertial frame. No observer ever overtakes a light beam and all observers measure light locally to be travelling at c. Hubble�s law is derived directly from the Robertson-Walker metric (Eq. 15), and is valid for all distances in any homogeneous, expanding universe.

The teardrop shape of our past light cone in the top panel of Fig. 1 shows why we can observe objects that are receding superluminally. Light that superluminally receding objects emit propagates towards us with a local peculiar velocity of c, but since the recession velocity at that distance is greater than c, the total velocity of the light is away from us (Eq. 20). However, since the radius of the Hubble sphere increases with time, some photons that were initially in a superluminally receding region later find themselves in a subluminally receding region. They can therefore approach us and eventually reach us. The objects that emitted the photons however, have moved to larger distances and so are still receding superluminally. Thus we can observe objects that are receding faster than the speed of light (see Section 3.3 for more detail).

How it affects the speed of light depends on the way you look at it. If you take the mean velocity, I think the speed of light does change, because the ratio current distance travelled in a certain time period is higher. However, the speed of light is per event the same and only the distance between the light and the object changes. The light itself never goes faster or slower (unless some controversial theories are true).

Woow amantine thanks, very interesting document.

however, I do think it is a stretch (if you don't mind the pun) to say that some photons actually escape and manage to trickle so to speak to us.

If light speed is constant then surely light has to travel ever further as the universe expands around it.

My orriginal point is that if the expansion of the universe is increasing in speed then at some point there is a cross over where light itself will appear to stand still. Of course light would still travel, just that the universe is expanding at exactly the same rate as light speed.

I believe that somthing similar happens just at the event horizon of a Black hole.

Any Further Thoughts?

Tim_UK74.

I always call it the delay of light, because if there was no delay the time of arrival would be 0.0000 but it reality it always take's some time

Tim,
It's a good idea that you made a different thread for your question in this thread. it's an interesting question.

Here's what I replied in that thread:
"You are right that the expansion of the universe is increasing, however I don't think it would reach the speed of light ever. The present rate of expansion is around 71 km/sec/Mpc (1 pc=3.26LY).

Also according to the latest WMAP data, the universe has a flat geometry and therefore, the universe will expand forever (reaching a max rate and then slowing down forever).

The rate of expansion depends on the nature of the mysterious dark energy that seems to repel gravity! So, these results of WMAP are capable of changes if dark energy's nature changes with time.

However, during the inflation period in the evolution of our universe, it grew to the factor of about 10^60 in less than 10^(-30) seconds. That's for sure was greater than the speed of light!"

Amantine's article is also interesting. I didn't know about the superluminally receding objects. I guess I have to read the whole article to understand the stuff.



[edit on 9-9-2004 by jp1111]

Tim, I think this is a great topic to explore. There so many reasons but I'll just name a few. I don't think a lot of people understand this. The people who respond to this are very smart but when it comes to ATS people just can't get a grasp of what this means.

Expansions of the universe is increasing, but this dosn't make sense does it? For example if you throw car keys up in the air what do they do?

They go higher but it slows down due to GRAVITY. Instead when it comes to the universe keys this is what's happening. You throw the keys up only to discovery it keeps going up at continuing faster speeds. That's strange isn't it?

Well scientists have concluded that the reason for this could be anti-gravity.

Iif this is true then we will eventually have to evaulate this question?

So, what does happen when the Universe goes past the speed of light?

I have my own theory which would suggest that since Einstein's equations say once you go above the speed of light time literally goes backwards time in the universe would go backwards.

This was mentioned on the Stephen Hawking's biography (1992).

What could happen is that people would die first and be born last.

Strange and perhaps raises some paradoxes amongst my listeners.

This is just one of the theories that might happen if the universe went faster than the speed of light.

I know there is some more, but if you wish to inverstigate this topic further,

I suggest you visit this website,

www.google.com

Hunt for the clues of the Universe. Tell me if you find anything new that should be brought up for this intrigueish discussion.

-Mystical Unicorn-

Amantime, So even though the object is travelling faster than light, it can't be considered that because the object is no one's frame? That doesn't make sense, so all along we have looking at c and saying it is the fastest because nothing have ever travelled faster than c in our frame?? So things can move faster than c, but not in our reference? Wow, that open a whole new prespective.

This is really amazing stuff. I was totally unaware of the whole Hubble sphere concept. I had to research and read over the stuff. I read several articles about expansion of the universe. Adding to amantine's article topic, here is an article that explains the superluminal recessive velocities in great details:
arxiv.org...

At the edge of this theoretical hubble sphere, the space expands at the speed of light and beyond the sphere the space expands at speeds greater than c. So, we would never receive information from objects that far!

surfup, I don't think it really means that an object can move faster than c because the restriction still applies if you are moving through space. Light still travels at c and nothing can travel faster than that. However, the space can expand at speeds greater than c and thus increase the distance between two objects at the speed of light or greater than that. Now, that does not mean that the object is actually travelling at >c, it's the space that's expanding at >c. So, it does not violate the relativity theories.
may be amantine could give more thoughts on this.

So space isn't made up of matter therefore it can travel faster than light? How about dark matter then?

As far as physics and particle accelerators work , an object gains mass as its speed increases (measurable at close to light speed , and proven in experiment) .

The reason physisists can't kick things over the light speed hurdle is because at light speed a particles mass will become hypotheticaly infinite , and need an infinite sorce of acceleration (power) .

It seems that even if the universe were infinite , all the objects would have to tap into all the energy to reach light speed .

If it does reach it however , all the stars and galxies would have long died and blinked out of site , so there would be no frame of reference to measure by .

Or so I thinks.....

Originally posted by surfup
So space isn't made up of matter therefore it can travel faster than light? How about dark matter then?

Hi surfup,

Accoriding to Quantum physics the fabric of space is filled with so called Virtual Particles which pop in and out of exsistance. Apparently the virtual particles anhilate themselves before they become real particles.

Thinking about it, could the virtual particles be the cause of the mysterious dark energy?


jp1111 - We are living in a time where people with an interest can research and formulate concepts, the propergation of these idea's can reall drive Humanities future. All Idea's are valid in science until disproved.


MysticalUnicorn - Thanks for your thoughts, I think you would be suprised how many people there are that can follow things at this level of complexity.

oddtodd - Cern are building the mother of all positron gliders.... have herd romours that with an accelerater the size of the one they are building that they will be able to detect the so called GOD particle... the source of Gravity Gravitron + so much more.....

All the Best People



Tim

Hi -

I believe that when we talk about the expansion of the Universe, we're talking about the expansion of space itself, not the objects that are within it. Einstein's SR theory only applies to the motion of particles/objects moving within the medium of space. Space itself has no limiting velocity, as far as I know.

So, in other words, space can expand at velocities greater than the speed of light. The speed of light is the limiting velocity for a particle's motion within the medium of space.

I hope that made sense ...


[edit on 9/9/2004 by netbound]

Originally posted by netbound
Hi -

I believe that when we talk about the expansion of the Universe, we're talking about the expansion of space itself, not the objects that are within it. Einstein's SR theory only applies to the motion of particles/objects moving within the medium of space. Space itself has no limiting velocity, as far as I know.

So, in other words, space can expand at velocities greater than the speed of light. The speed of light is the limiting velocity for a particle's motion within the medium of space.

I hope that made sense ...


[edit on 9/9/2004 by netbound]

Hi Netbound

Yeah I know what you are getting at but actually all physical object ocupie space and the only reason the exapansion doesn't seem to effect the objects is that the rate within a smjall locolaised area is so small that no change seems to take place.

But if all of space expanded at the speed of light then all matter would be stretched appart.....

This actually does happen past the point of an event horizon of a black hole. Matter is litrally stretched appart, this is called spagettification.

-

The more I think about what people have said the more the entire universe seems to fit the model of being the exact oposit of a black hole.

maybe the BIG Bang is what happens after the point of Singularity....

-

More thoughts when I should be working lol )

Tim.

Originally posted by surfup
So space isn't made up of matter therefore it can travel faster than light? How about dark matter then?

As I said earlier, space is not travelling, it's expanding. Expansion of space is not the same as travelling through space.

Moreover,
we know there is no contradiction with special relativity when faster than light motion
occurs outside the observer�s inertial frame. General relativity was specifically derived
to be able to predict motion when global inertial frames were not available. Galaxies
that are receding from us superluminally are at rest locally (their peculiar velocity,
vpec = 0) and motion in their local inertial frames remains well described by special
relativity. They are in no sense catching up with photons (vpec = c). Rather, the
galaxies and the photons are both receding from us at recession velocities greater than the speed of light...
The general relativistic interpretation of the expansion interprets
cosmological redshifts as an indication of velocity since the proper distance between
comoving objects increases. However, the velocity is due to the rate of expansion
of space, not movement through space, and therefore cannot be calculated with the
special relativistic Doppler shift formula. Hubble & Humason�s calculation of velocity
therefore should not be given special relativistic corrections at high redshift, contrary
to their suggestion.

From: www.arxiv.org...

Originally posted by tim_uk74
jp1111 - We are living in a time where people with an interest can research and formulate concepts, the propergation of these idea's can reall drive Humanities future. All Idea's are valid in science until disproved.

I understand that and I respect that. I just read a lot of stuff over expansion and I realized that the argument of putting 71km/sec/Mpc against the expansion of space reaching c does not make sense as I did not explain it.

From what I have read, hubble sphere is an imaginary sphere that has us in the center and consists of all the observable universe around us. So objects beyond this sphere are receding at speeds v(rec)>c and thus cannot be seen. However, the hubble sphere itself is expanding faster than the objects beyond the horizon of the sphere and that's why some of these objects that are receding at speeds greater than c will then recede at speeds less than c when the imaginary horizon of the sphere moves past them and thus will be observed.

Now, this hubble sphere concept is applicable to every single point in the universe. Therefore, for some observer on a very distant galaxy, if we are out of their hubble sphere then we are receding at speeds >c relative to that observer.

Also, the value of H = 71km/sec/Mpc means that the objects (galaxies, etc.) 1 Mpc (1pc=3.26LY) away from us are moving at the rate of 71km/sec relative to us. Objects >1Mpc farther would not be receding at 71km/sec, rather they would be receding faster and faster as the distance increases. It is estimated here that objects 4200 Mpc away are already receding at the speed of light.

I would recommed reading this article: curious.astro.cornell.edu...
It seems to explain this topic, however, I'm a little confused in understanding it.

Edit: In short, to answer the original question.

tim_uk74
Has anyone contemplated that as the speed of the expansion of the universe is increasing, what happens when the expansion speed equals that of the speed of light

The expansion rate is already greater than the speed of light over large distances relative to us. For smaller distances, it is smaller than the speed of light. So when the stretching of space moves our nearby galaxies to a large distance, they will be receding at speeds greater than light also. However, for very close galaxies, like Andromeda and ours, gravity wins over expansion.

Sorry for the confusion earlier.

[edit on 14-9-2004 by jp1111]

Originally posted by jp1111
As I said earlier, space is not travelling, it's expanding. Expansion of space is not the same as travelling through space.

Ahh. Got it now. Space is expanding. Thanks.

Originally posted by tim_uk74
.... expansion of the universe is increasing in speed then at some point there is a cross over where light itself will appear to stand still. Of course light would still travel, just that the universe is expanding at exactly the same rate as light speed.

I believe that somthing similar happens just at the event horizon of a Black hole.

It's entirely different case.
In black holes so much matter is packed to so small space that gravity is so strong that escape velocity is/bigger than lightspeed.
And there's also other reason, space itself is curved on itself so there's no direction where you could go "up".
curious.astro.cornell.edu...

Hi E_T,

yeah I know t's a different case I said somthing similar. my thoughts were that if space time is accelerating in expansion and this acceleration is constant then matter would be ripped appart in a spagetification style way.

So E_T do you think that S Hawking conceding on his bet about black holes leaking information is correct?

Also do you think that Black holes are BIG FUZZY BALLS heheh or do you follow that there is a singularity?

Also as chaos theory suggests order comes from chaos.... so if this follows then I wonder if there is some structure to the insides of a black hole rather than the quantum foam that people talk about.

All the best people

Tim...

1. What if space is not expanding but matter is uniformly shrinking? The Universe is not getting bigger but we are getting smaller? (Just a thought)
2. What if the 'expansion' of the Universe is time? Sort of if you could contract the Universe you could run time backwards. Like reading a CD backwards instead of forwards. Sort of like it is gear driven. You could run the Universe forwards and backwards to re-play a favorite part.

It is nice to see physicists loosen up their ideas on time (and hopefully some other constants of the Universe) and realize things that seem eternal may change over a long enough period of time. What is right now may not have always been.

The weird thing is if time itself changes how could you ever perceive it? What if the Universe just stands still for a trillion years then starts up again? How would we ever know? Would it be almost an instantaneous little slur in our perceptions? Or could it be done so smoothly we just didn't know at all?

more psycho babble,
What about space, what is it really? is it length? in three dimensions? In a huge cube of space could it be that it has 'grain'. Going from corner B to it's opposite coner, B', takes just a bit more time than going from corner A to A'? Or would it mean our original cube was not quite square, or that space was skewed. I wonder if there may be flow of space. Perhaps it would not be 'grain' of the Universe but going with the current of the Universe or against it. Anyone think in string theory there may be length/dimension particles/strings? they would have to be some of the most hyperfluid particles around. What about time particles/strings?

omg where are my meds!
.

I have a weird theory..that the universe is already expanding at the speed of light because it's fabric is space time...so because of the idea that travelling faster than light will send you back in time...I think that we're all travelling at the speed of light through a physical kind of time. That would mean all time exists together and our experience of time is just the process of travelling through it. So maybe the universe isn't expanding but we're just moving through the process of it expanding...which may have happened already.

In any case - the question of "what is the universe expanding into" is an interesting one. My guess is itself - space time is kind of "collapsing" if you will, into the fifth dimension. This is assuming the theory of the 6 curled up dimensions is right. Which I think it might be.

Oh bloody hell, I hope I have made that more confusing than it is.

Here's an ignorant question regarding the expansion of the universe...does Newtons Third Law not apply? "For every action, there is an equal and opposite reaction"
If it does how would this affect the Universe?