Do you believe in life elsewhere?

[sloasdaylight]

I just realized the time, and if I don't come to bed, I might as well be living on Alpha Centauri as far as future sexy time with my lady friend will be concerned. I'm fascinated by this though, and I look forward to reading your replies 12, thanks for the discussion

 

[12bass]

so, there is some "magical" distance that a star can be from us, where light from the star would never reach us?

how can this be, since all matter in the universe was once concentrated at a singularity the instant before the big bang?

How can it be? The Big Bang theory posits that the initial distance between all points was 0. However, if at some point the rate of expansion of spacetime became greater than c, then light can no longer traverse it.

One analogy is a balloon. If you're on the surface of an infinitely expanding balloon and are limited to a velocity of 1 mm per second, but the balloon is expanding at 2 mm per second, then certain parts of the surface of the balloon are no longer accessible to you, no matter how long you travel.

 

[12bass]

I just realized the time, and if I don't come to bed, I might as well be living on Alpha Centauri as far as future sexy time with my lady friend will be concerned. I'm fascinated by this though, and I look forward to reading your replies 12, thanks for the discussion

You're welcome. I'm fascinated by this stuff too and struggle to understand it myself. Our brains are not well adapted to thinking of non-Euclidean space or the bizarre effects of relativity. In our normal, day-to-day, lives, we can quite reasonably assume that space and time are linear and that velocities add together. One notable exception, however, is the GPS system that many of us now rely on for navigation - it would lose accuracy in a couple of minutes without constant corrections for relativistic effects.

GPS and Relativity

 

[Lonesomedave]

well, thank you also, for at least giving me something to think about.

i still think the theory falls apart (or my ability to understand it certainly does) because at the big bang all matter was concentrated at a singularity... therefore, it should be impossible for any piece of that matter to have moved so far away that it's light cannot reach us.... get back to me.. if not tomorrow, well... in the future... but still, thanks

 

[12bass]

Nice series of videos which explore the topic:

John C. Mather - The Story of the Universe (part 1 of 7) - YouTube

 

[JacoLesFlea]

yes

 

[BassyBill]

Just as an interesting aside - the idea that we couldn't travel intergalactic distances in a human lifetime is a misconception in one very important respect. It depends whose lifetime you are talking about.

For instance, suppose we use our hypothetical spaceship to travel to Andromeda, 2.5 million light years away. We accelerate at 1G for the first half of the journey and then decelerate at 1 G for the second. The journey would take 2501732.6 years, Earth time, and you'd be close to the speed of light for a very significant portion of it.

To someone travelling on the ship, it would take just 28.6 years, due to time dilation effects.

 

[ifender]

I believe in other universes

 

[12bass]

For instance, suppose we use our hypothetical spaceship to travel to Andromeda, 2.5 million light years away. We accelerate at 1G for the first half of the journey and then decelerate at 1 G for the second. The journey would take 2501732.6 years, Earth time, and you'd be close to the speed of light for a very significant portion of it.

To someone travelling on the ship, it would take just 28.6 years, due to time dilation effects.

Time dilation effects do come in handy.... On the other hand, only massless particles like photons can actually reach c. Things which have significant mass (like you and me and space ships) would require immense amounts of energy to accelerate to near light speed (and take advantage of time dilation). One reason why accelerators like the LHC are so big and expensive is that it requires a lot of energy to accelerate "heavy" particles like protons. So... no free lunch for intergalactic travel until we find a better source energy for propulsion....

 

[BassyBill]

Time dilation effects do come in handy.... On the other hand, only massless particles like photons can actually reach c. Things which have significant mass (like you and me and space ships) would require immense amounts of energy to accelerate to near light speed (and take advantage of time dilation). One reason why accelerators like the LHC are so big and expensive is that it requires a lot of energy to accelerate "heavy" particles like protons. So... no free lunch for intergalactic travel until we find a better source energy for propulsion....

All very true. The time dilation effects could come in handy, but only at speeds close to c, and at those speeds it's not just the energy costs that would be pose huge difficulties. Space is pretty empty, but not totally so, and the amounts of energy released in collisions even with very tiny particles would be disastrous for any spaceship travelling at such high velocity. How could you move stuff out of the way?

 

[12bass]

Perhaps a deluxe windscreen would be in order....

 

[Lonesomedave]

please, bill or 12bass or someone... straighten me out on the concept i raised last night and still cannot get my head around--and BTW correct any of my factual assumptions that are wrong.

the moment before the big bang, all matter in the universe was concentrated of the singularity that was about to explode (for lack of a better word) and create the universe as we know it...r.i.g.h.t?

the moment after the big bang, the universe expanded and is still doing so today..right?

the fabric of spacetime, not being materiel was not limited by the speed of light, and so could expand at whatever speed such things happen.. say 3(c) or even infinite(c)...right?

the particles which were destined to become matter in our universe, however, being material, WERE limited by einstein's laws to a maximum speed of c... right?

correct me if i am off course on any of this.

so, therefore, given all of the above, how is it possible for ANY of those particles- whether they now exist in the form of stars or whatever form they might exist-- to be so far away from us that their light can never reach us?... it just does not make sense.

and, if it is possible, how come that does not apply to every star everywhere?

is there some magical distance that a star has to be away from us for it's light to never reach us? and if that is true, let's call the distance M for "magical"...then what happens if a star is not at the distance M but instead is at the distance (M -1foot)?

or say a star sits right on the line that denotes M... could half of the star's light reach us and half not reach us?...sorry for my obtuseness but i just can't grasp these concepts.

 

[Muaguana]

please, bill or 12bass or someone... straighten me out on the concept i raised last night and still cannot get my head around--and BTW correct any of my factual assumptions that are wrong.

the moment before the big bang, all matter in the universe was concentrated of the singularity that was about to explode (for lack of a better word) and create the universe as we know it...r.i.g.h.t?

the moment after the big bang, the universe expanded and is still doing so today..right?

the fabric of spacetime, not being materiel was not limited by the speed of light, and so could expand at whatever speed such things happen.. say 3(c) or even infinite(c)...right?

the particles which were destined to become matter in our universe, however, being material, WERE limited by einstein's laws to a maximum speed of c... right?

correct me if i am off course on any of this.

so, therefore, given all of the above, how is it possible for ANY of those particles- whether they now exist in the form of stars or whatever form they might exist-- to be so far away from us that their light can never reach us?... it just does not make sense.

and, if it is possible, how come that does not apply to every star everywhere?

is there some magical distance that a star has to be away from us for it's light to never reach us? and if that is true, let's call the distance M for "magical"...then what happens if a star is not at the distance M but instead is at the distance (M -1foot)?

or say a star sits right on the line that denotes M... could half of the star's light reach us and half not reach us?...sorry for my obtuseness but i just can't grasp these concepts.

Distance has little to nothing do with it. If you've taken an elementary physics course, you'd realize that this is a velocity quandary, not a matter of distance. So if the distance between two objects is increasing faster than the speed of light due to spacetime expanding, the light from the objects can't reach each other because photons are limited to traveling at the speed of light. Any time the term "magical" appears from your mouth in a discussion about science, it means you need to read more.

 

[Lonesomedave]

Distance has little to nothing do with it. If you've taken an elementary physics course, you'd realize that this is a velocity quandary, not a matter of distance. So if the distance between two objects is increasing faster than the speed of light due to spacetime expanding, the light from the objects can't reach each other because photons are limited to traveling at the speed of light. Any time the term "magical" appears from your mouth in a discussion about science, it means you need to read more.

or be educated by bright fellows like you here on talkbass....

substitute to word "critical" then for "magic"

and you have not answered my question... only provided an obvious answer that i already knew.

WHAT determines when the speed of recession will exceed the speed of light?

is it or is it not a function of the distance the two objects are apart?

clearly, we can see light from alpha centauri, so it must not be receding from us at greater than the speed of light...if, indeed it is receding at all, since the phenomenon of universal expansion seems to limited to to galaxies rather than stars withing one galaxy.

so, let's look at our nearest galactic neighbor that IS receding from us... whatever that is.

we can still see it's light, right?

so, whatever the determining factor for velocity, it's velocity of recession, we'll agree, is less than c...right?

my question is twofold. what is the determining factor in whether the speed of recession is greater or lesser than c?

and secondly, how can this be possible, since all matter started at the same time and place ie the big bang.

since c is the absolute limit of speed for matter, and since all matter originally started at the point of the big bang singularity, and since that time the matter cannot possibly have traveled away from us at a speed which exceeds c, how can it be possible for any particle of matter to emit radiation that cannot reach us?

and, boy, you must have some bright people where you come from if THIS is elementary physics to you.

 

[Muaguana]

or be educated by bright fellows like you here on talkbass....

substitute to word "critical" then for "magic"

and you have not answered my question... only provided an obvious answer that i already knew.

WHAT determines when the speed of recession will exceed the speed of light?

is it or is it not a function of the distance the two objects are apart?

clearly, we can see light from alpha centauri, so it must not be receding from us at greater than the speed of light...if, indeed it is receding at all, since the phenomenon of universal expansion seems to limited to to galaxies rather than stars withing one galaxy.

so, let's look at our nearest galactic neighbor that IS receding from us... whatever that is.

we can still see it's light, right?

so, whatever the determining factor for velocity, it's velocity of recession, we'll agree, is less than c...right?

my question is twofold. what is the determining factor in whether the speed of recession is greater or lesser than c?

and secondly, how can this be possible, since all matter started at the same time and place ie the big bang.

since c is the absolute limit of speed for matter, and since all matter originally started at the point of the big bang singularity, and since that time the matter cannot possibly have traveled away from us at a speed which exceeds c, how can it be possible for any particle of matter to emit radiation that cannot reach us?

and, boy, you must have some bright people where you come from if THIS is elementary physics to you.

Answer to first question: The acceleration of the universe's expansion.

Answer to second equation: The freakin' acceleration of the universe's expansion. You do know what acceleration means, right? If so, this should follow simple logic. If you don't, maybe you know what Google is so you can look it up.

And cut the "bright" bull****, you're not fooling anyone with your smug attempts at sarcasm.

 

[BassyBill]

Dave - the further you are aware from something, the faster that region of space is expanding away from your relative position. For near objects, the expansion rate is less than c and we can see them. For objects further away, the rate may still be less than c and we can in principle see them when light arrives here from them in the future. For objects far enough away that the expansion rate is greater than c, we can never observe them. The objects themselves aren't travelling faster than light, it's just that the region of space they occupy is getting further away from us. And you're right, there is a critical distance (see linked article).

Difficult to get one's head around, I know.

Observable universe - Wikipedia, the free encyclopedia

 

[sloasdaylight]

Distance has little to nothing do with it. If you've taken an elementary physics course, you'd realize that this is a velocity quandary, not a matter of distance. So if the distance between two objects is increasing faster than the speed of light due to spacetime expanding, the light from the objects can't reach each other because photons are limited to traveling at the speed of light. Any time the term "magical" appears from your mouth in a discussion about science, it means you need to read more.

Velocity is

, so unless I'm seriously misunderstanding something, which is possible, given it's been 8 years since I've taken a physics course, the distance between two items absolutely has something to do with it.

 

[sloasdaylight]

Dave - the further you are aware from something, the faster that region of space is expanding away from your relative position. For near objects, the expansion rate is less than c and we can see them. For objects further away, the rate may still be less than c and we can in principle see them when light arrives here from them in the future. For objects far enough away that the expansion rate is greater than c, we can never observe them. The objects themselves aren't travelling faster than light, it's just that the region of space they occupy is getting further away from us. And you're right, there is a critical distance (see linked article).

Difficult to get one's head around, I know.

Observable universe - Wikipedia, the free encyclopedia

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?

 

[Muaguana]

Velocity is

, so unless I'm seriously misunderstanding something, which is possible, given it's been 8 years since I've taken a physics course, the distance between two items absolutely has something to do with it.

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.

 

[Lonesomedave]

Answer to first question: The acceleration of the universe's expansion.

Answer to second equation: The freakin' acceleration of the universe's expansion. You do know what acceleration means, right? If so, this should follow simple logic. If you don't, maybe you know what Google is so you can look it up.

And cut the "bright" bull****, you're not fooling anyone with your smug attempts at sarcasm.

you need to take a chill pill...

i thought i raised legitimate questions and if not..well, sorry