Do you believe in life elsewhere?

[sloasdaylight]

You have no idea what I'm talking about, so please don't bother talking to me. Read a book. Read anything, really, just don't butt into a conversation you can't comprehend.

I've spent the last 2 days and the last entire page of this thread trying to understand this notion that space-time travels faster than the speed of light, but that elements within a region of space-time travelling faster than the speed of light aren't travelling faster.

If you want to be a dick about this then that's your call, but please, explain how a question that is centered around velocity doesn't have anything to do with the distance between two objects.

 

[Lonesomedave]

See, this is the thing I'm having an issue with. If the area or space they occupy is travelling faster than the speed of light, why are the objects within that area of space not moving faster than the speed of light as well?

thanks bill...

i have the same problem and also, i guess another problem is how far away must they be to be receding at greater than c?

however, I have now figured out one possible mechanism for even very near objects to be receding at greater than c...

suppose just a few seconds after the big bang, one particle and another particle were ejected out of the singularity but in exactly opposite directions... let's further suppose that the speed of each was 80% of c.

would they not be moving away from each other at a sum of 160% of c?

just like when two cars, each traveling at 30 mph, are moving in opposite directions on a road... the sum total of the speed of separation is 60 mph... right?

 

[sloasdaylight]

thanks bill...

i have the same problem and also, i guess another problem is how far away must they be to be receding at greater than c?

however, I have now figured out one possible mechanism for even very near objects to be receding at greater than c...

suppose just a few seconds after the big bang, one particle and another particle were ejected out of the singularity but in exactly opposite directions... let's further suppose that the speed of each was 80% of c.

would they not be moving away from each other at a sum of 160% of c?

just like when two cars, each traveling at 30 mph are moving in opposite directions on a road... the sum total of the speed of separation is 60 mph... right?

The distance away from us is irrelevant to how fast they're moving away from us.

In response to the second bold, relatively they're moving away faster than the speed of light, but in reality they are still each moving away from a center point at .8c, so no theories are being broken.

 

[Lonesomedave]

The distance away from us is irrelevant to how fast they're moving away from us.

In response to the second bold, relatively they're moving away faster than the speed of light, but in reality they are still each moving away from a center point at .8c, so no theories are being broken.

no, no, that wasn't my point.. i know that no theories are being broken.

my point was that since the combined speed of regression is 160% of c, then if one particle emitted light, it would not reach the other particle...r.i.g.h.t?

 

[sloasdaylight]

no, no, that wasn't my point.. i know that no theories are being broken.

my point was that since the combined speed of regression is 160% of c, then if one particle emitted light, it would not reach the other particle...r.i.g.h.t?

Right.

 

[BassyBill]

Right.

No, wrong. Sorry.

According to special relativity (in a flat region of spacetime), if you measure the speed of any object (with mass) relative to another, the speed will always be less than c. And the speed of light you measure from an object will always be c, regardless of your own motion towards or away from it. What actually changes depending on relative motion is the speed at which time appears to go on each of the two objects from an observer's point of view on each object.

But in expanding/curved spacetime (general relativity), the expansion itself can affect the outcome with the result that light cannot travel from one region to another. Imagine an ant running along a length of stretchy rubber. If you can stretch the rubber far enough and fast enough, the ant will never get to the end no matter how fast it runs relative to any other region of the rubber.

Don't expect to understand this in the way that we normally "understand" concepts like space, distance, speed and time. Our intuitive, "common sense" understanding of these concepts, based on local experience, is just incorrect.

 

[sloasdaylight]

No, wrong. Sorry.

According to special relativity (in a flat region of spacetime), if you measure the speed of any object (with mass) relative to another, the speed will always be less than c. And the speed of light you measure from an object will always be c, regardless of your own motion towards or away from it. What actually changes depending on relative motion is the speed at which time appears to go on each of the two objects from an observer's point of view on each object.

But in expanding/curved spacetime (general relativity), the expansion itself can affect the outcome with the result that light cannot travel from one region to another. Imagine an ant running along a length of stretchy rubber. If you can stretch the rubber far enough and fast enough, the ant will never get to the end no matter how fast it runs relative to any other region of the rubber.

Don't expect to understand this in the way that we normally "understand" concepts like space, distance, speed and time. Our intuitive, "common sense" understanding of these concepts, based on local experience, is just incorrect.

So if the relative speed of two objects moving away from each other is greater than c, a photon emanated from 1 object will still reach the other one?

 

[BassyBill]

So if the relative speed of two objects moving away from each other is greater than c, a photon emanated from 1 object will still reach the other one?

The relative speed of two objects moving away from each other can not be greater than c (in flat spacetime). You can't fire two particles in opposite directions at 0.8c and then say they're moving apart from each other at 1.6c. Their speeds measured by an observer who fired them in different directions would be 0.8c in each case. But the relative speed of one measured by an observer riding on the other would still be less than c. Time, motion and distance are not absolute - they all depend on the relationship between the observer's viewpoint and what is being measured.

By the way, this was also a possible point of confusion:

The distance away from us is irrelevant to how fast they're moving away from us.

The further away something is from us, then the faster space is expanding at that point relative to us.

 

[Lonesomedave]

The relative speed of two objects moving away from each other can not be greater than c (in flat spacetime). You can't fire two particles in opposite directions at 0.8c and then say they're moving apart from each other at 1.6c. Their speeds measured by an observer who fired them in different directions would be 0.8c in each case. But the relative speed of one measured by an observer riding on the other would still be less than c. Time, motion and distance are not absolute - they all depend on the relationship between the observer's viewpoint and what is being measured.

By the way, this was also a possible point of confusion:



The further away something is from us, then the faster space is expanding at that point relative to us.

ok, bill, i accept that.. i may not understand it, but i accept it.

so, if this question has an answer..

in the example of two object moving directly away from each other at .8c... how fast ARE they moving apart... i mean, lets say they started out at the same point and instantly accelerated to .8c

after 1 second the would be (186,000 x 2) x .8 miles apart, r.i.g.h.t? or whatever the math is.

so, how could you not say they achieved this by have a combined speed of greater than c?

 

[BassyBill]

ok, bill, i accept that.. i may not understand it, but i accept it.

so, if this question has an answer..

in the example of two object moving directly away from each other at .8c... how fast ARE they moving apart... i mean, lets say they started out at the same point and instantly accelerated to .8c

after 1 second the would be (186,000 x 2) x .8 miles apart, r.i.g.h.t? or whatever the math is.

so, how could you not say they achieved this by have a combined speed of greater than c?

Because the faster two things are moving relative to each other, the more distance and time change on one compared to the other.

If an observer on one object measured the speed of the other one by taking two measurements of distance over a time interval, the distance it had travelled would be a lot shorter and the time that it had taken would be a lot longer than these quantities would be recorded by somebody on the other object. So that would make the second object's speed much lower as measured by the person on the first object.

 

[Lonesomedave]

Because the faster two things are moving relative to each other, the more distance and time change on one compared to the other.

If an observer on one object measured the speed of the other one by taking two measurements of distance over a time interval, the distance it had travelled would be a lot shorter and the time that it had taken would be a lot longer than these quantities would be recorded by somebody on the other object. So that would make the second object's speed much lower as measured by the person on the first object.

i bow to you...but my head is swimming. but one final question on this subject and i'll let it go.

suppose you had the situation just described, and you had an observer at the starting point.

and let's say he had a stopwatch that started the instant the objects begin moving.

and lets say that after a period of one second, the stopwatch stopped AND both objects immediately came to a halt.

then let's say he went to one object and measured the distance to the other object... how far apart would the objects be?

 

[Jazz Ad]

It can be anything depending on the confitions but it will still be less than 2 light seconds.
You will fail if you try to understand this with analogies at our scale.

 

[BassyBill]

It can be anything depending on the confitions but it will still be less than 2 light seconds.
You will fail if you try to understand this with analogies at our scale.

Exactly - these sort of analogies always break down because they ignore the fundamental aspect of Einstein's insight. What's being asked for is an absolute distance between two objects and there is no such thing. Distance, speed, time and location in space are NOT in any way absolute quantities. They all vary according to the relative motion of the measurer with respect to whatever is being measured, especially when speeds near to that of light are involved in the calculation.

 

[Jazz Ad]

When you're done understanding the way things work at the cosmic scale, try subatomics.
It's even more fun.

 

[Waterpilot]

This thread either makes me feel dumber then I am or as dumb as I am and I'm too dumb to figure out which it is. I think something in my head just broke.

 

[nutdog]

You have no idea what I'm talking about, so please don't bother talking to me. Read a book. Read anything, really, just don't butt into a conversation you can't comprehend.

Sheldon?

 

[pica]

If there's a bright center to the universe, we're on the planet that it's farthest from.

Well said.

 

[pica]

Well, after posting this about a week ago I was surprised to see what a hot topic this thread was. As of now it has 11,254 views with 376 responses. I thought you had some really good well thought out answers.

It was interesting to see how the thread went from life on other planets to "what is life" to people talking about everything from science, superstition, aliens, to who built the pyramids.

Well I haven't given my answer yet. I was saving that for the end. With all the trillions of planets in the universe, It's hard not to imagine that one of those planets is capable of sustaining life. I doubt we'll ever find out in my lifetime but I'd like to think we will someday.