Astronomy & Space Exploration

[Maroon Lucifer]

Can anyone answer me this. It's been bugging me for a while.
According to the Big Bang Theory, everything was created at the same point in space, and has been moving away from that point ever since. Why, then, are the Milky Way and the Andromeda galaxy colliding in a few billion years time. Shouldn't both have the same trajectory from the original explosion, and thus moving away from each other?
I don't know if that made any sense.

 

[nimic]

Can anyone answer me this. It's been bugging me for a while.
According to the Big Bang Theory, everything was created at the same point in space, and has been moving away from that point ever since. Why, then, are the Milky Way and the Andromeda galaxy colliding in a few billion years time. Shouldn't both have the same trajectory from the original explosion, and thus moving away from each other?
I don't know if that made any sense.

The expansion of space is only noticeable at really, really big scales. As in much bigger than the distance between the Milky Way and Andromeda galaxies. So there are quite a few galaxies out there that we won't necessarily be moving away from. But there are many, many more that are moving away from us. In fact, eventually the expansion of space will exceed the speed of light, at which point there are galaxies that we will literally never be able to see again, since the distances between us will increase faster than light can travel through them.

Also, it's not really a trajectory from an original explosion as such. In a way we're not even moving further away from other galaxies at all, rather it is space itself that is expanding. Distances are simply becoming intrinsically larger. Nor is there any "middle" of the Universe that everything is moving away from. Actually, everywhere is the middle, and at large enough scales everything is moving away from everything.

 

[Il Prete Rosso]

Can anyone answer me this. It's been bugging me for a while.
According to the Big Bang Theory, everything was created at the same point in space, and has been moving away from that point ever since. Why, then, are the Milky Way and the Andromeda galaxy colliding in a few billion years time. Shouldn't both have the same trajectory from the original explosion, and thus moving away from each other?
I don't know if that made any sense.

Or maybe this is just a load of shit....just saying. Sometimes you may need to realize humans are smart enough to ask a lot of questions...but not smart enough to figure all out.

 

[nimic]

Or maybe this is just a load of shit....just saying. Sometimes you may need to realize humans are smart enough to ask a lot of questions...but not smart enough to figure all out.

The expansion of space is not exactly one of those, though. We have a very solid understanding of it. The big bang itself is one of the surest things we have in science, since the evidence for it is all around.

 

[Ubik]

In the same way that particles still managed to fuse to make molecules, asteroids, planets, stars and galaxies themselves. We're just gravitationally locked with Andromeda, as we are with the minor galaxies that orbit us.

 

[adexkola]

The expansion of space is only noticeable at really, really big scales. As in much bigger than the distance between the Milky Way and Andromeda galaxies. So there are quite a few galaxies out there that we won't necessarily be moving away from. But there are many, many more that are moving away from us. In fact, eventually the expansion of space will exceed the speed of light, at which point there are galaxies that we will literally never be able to see again, since the distances between us will increase faster than light can travel through them.

Also, it's not really a trajectory from an original explosion as such. In a way we're not even moving further away from other galaxies at all, rather it is space itself that is expanding. Distances are simply becoming intrinsically larger. Nor is there any "middle" of the Universe that everything is moving away from. Actually, everywhere is the middle, and at large enough scales everything is moving away from everything.

So you're getting fatter every moment?

 

[nimic]

In the same way that particles still managed to fuse to make molecules, asteroids, planets, stars and galaxies themselves. We're just gravitationally locked with Andromeda, as we are with the minor galaxies that orbit us.

And many other galaxies. Was it our entire super cluster, maybe? I can't keep track of all these designations.

 

[Maroon Lucifer]

...Nor is there any "middle" of the Universe that everything is moving away from. Actually, everywhere is the middle, and at large enough scales everything is moving away from everything.

If everything is moving away from everything, surely that implies that nothing is moving towards anything else? Otherwise that sentence makes no sense to me. And should that be true, our galaxy shouldn't collide with another?
The only way the Milky Way+Andromeda collide makes sense for me, is that both have been affected by each others' gravitational pull for the last 14+ billion years, and the only way for them to collide, is either for both of them to lose momentum, or there is an increase in gravitatinoal pull.

 

[nimic]

If everything is moving away from everything, surely that implies that nothing is moving towards anything else? Otherwise that sentence makes no sense to me. And should that be true, our galaxy shouldn't collide with another?
The only way the Milky Way+Andromeda collide makes sense for me, is that both have been affected by each others' gravitational pull for the last 14+ billion years, and the only way for them to collide, is either for both of them to lose momentum, or there is an increase in gravitatinoal pull.

Everything is moving away from everything, but up until a certain scale gravity is a stronger force than the expansion of space. So while the Milky Way and Andromeda are heading towards each other, they are both still part of a Supercluster that is headed in a certain direction.

It's like Ubik said:

In the same way that particles still managed to fuse to make molecules, asteroids, planets, stars and galaxies themselves. We're just gravitationally locked with Andromeda, as we are with the minor galaxies that orbit us.

 

[MrMarcello]

 

[Dracula]

Can anyone answer me this. It's been bugging me for a while.
According to the Big Bang Theory, everything was created at the same point in space, and has been moving away from that point ever since. Why, then, are the Milky Way and the Andromeda galaxy colliding in a few billion years time. Shouldn't both have the same trajectory from the original explosion, and thus moving away from each other?
I don't know if that made any sense.

So you're getting fatter every moment?

If everything is moving away from everything, surely that implies that nothing is moving towards anything else? Otherwise that sentence makes no sense to me. And should that be true, our galaxy shouldn't collide with another?
The only way the Milky Way+Andromeda collide makes sense for me, is that both have been affected by each others' gravitational pull for the last 14+ billion years, and the only way for them to collide, is either for both of them to lose momentum, or there is an increase in gravitatinoal pull.

didnt watch that youtube vid so i dont know if that explains it better. I always had these questions too...i think i now understand it better....

The big bang theory doesnt say everything came from one point, in fact the 'theory', or at least the common understanding of that theory says almost the opposite. Bear in mind that before the big bang there was no space...no time...no nothing. The universe simply came into existence one day.

Its easy to think big bang...then there is now expansion, therefore we are all expanding from one point, but we are not. The universe is expanding from everywhere to everywhere. There's the old balloon method of understanding that concept - you have a deflated baloon, draw two dots on it 1cm apart then blow the balloon up...the two dots will expand apart from each other but they are not expanding from a single point, but every point. Its the fabric of space that is expanding. It's also expanding faster than the speed of light. We know this due to the 'red shift' when observing far away galaxies. This is a result of the light waves being 'stretched', in that the photons that make up light on their merry way from a far away galaxy to our eyes end up having the space in which they travel expand before they can get to their destination. Now, i think that the galaxies that are furthest away are expanding away faster than those closest...so andromeda (our nearest galaxy) is not expanding away faster than speed of light but the further away ones are because the further away they are from you the faster the space expands. Now, the real head f##k is that this is the same from every vantage point in the universe so space is expanding faster the further away everything is away from everything...i think. It has something to do with the universe having to be homogenous from everywhere...space expansion must equal itself out, like how if you have a really big stick, you point it away from you and turn, the end of the stick closest to you is travelling slowly, yet the end of the stick furthest away from you is travelling really fast in 'space' in comparison. I thnk thats how it was explained to me

So are we expanding? Getting fatter? No, apparently not. The gravitational forces that bind us on an atomic level are significantly stronger than the expansion of space. This is the same for galaxies/solar systems themselves, they are not expaning from within themselves but the space around them is. Bit convenient that i always think.

The reason why galaxies collide is that as well as the previous point that gravitational forces are much stronger than that of the expanding universe (think of it in the same way a fridge magnet can overcome the earths gravitational pull - gravity holds the bloody moon where it is but a fridge magnet can overcome that force!) and all matter in the universe is attracted to each other by gravity, but also galaxies are moving around in space freely anyway, like a bit of flotsom on water, so at some point its always going to happen that galaxies will collide.

I have no idea if any of that made sense...i just started typing and got carried away

 

[nimic]

It's also expanding faster than the speed of light. We know this due to the 'red shift' when observing far away galaxies. This is a result of the light waves being 'stretched', in that the photons that make up light on their merry way from a far away galaxy to our eyes end up having the space in which they travel expand before they can get to their destination.

Just one correction. It's not expanding faster than the speed of light, or we wouldn't have been able to receive the red-shifted light in the first place. It will expand faster than the speed of light eventually, though, at which point there are galaxies we will never be able to "see" again, no matter how long the light gets to travel.

Or rather, the rate of expansion depends on how far away from us it is. So objects that we are seeing redshifted light from might be expanding away from us faster than the speed of light now, but they weren't when the light we are currently seeing was emitted (or we wouldn't have seen the light in the first place).

It's not a simple subject, and I wouldn't say I really grasp it myself. I grasp the concept of it, which is good enough for me when it comes to physics.

 

[Dracula]

Just one correction. It's not expanding faster than the speed of light, or we wouldn't have been able to receive the red-shifted light in the first place. It will expand faster than the speed of light eventually, though, at which point there are galaxies we will never be able to "see" again, no matter how long the light gets to travel.

Or rather, the rate of expansion depends on how far away from us it is. So objects that we are seeing redshifted light from might beexpanding away from us faster than the speed of light now, but they weren't when the light we are currently seeing was emitted (or we wouldn't have seen the light in the first place).

It's not a simple subject, and I wouldn't say I really grasp it myself. I grasp the concept of it, which is good enough for me when it comes to physics.

Yep, your second paragraph is how I understand it

 

[Revan]

didnt watch that youtube vid so i dont know if that explains it better. I always had these questions too...i think i now understand it better....

The big bang theory doesnt say everything came from one point, in fact the 'theory', or at least the common understanding of that theory says almost the opposite. Bear in mind that before the big bang there was no space...no time...no nothing. The universe simply came into existence one day.

Its easy to think big bang...then there is now expansion, therefore we are all expanding from one point, but we are not. The universe is expanding from everywhere to everywhere. There's the old balloon method of understanding that concept - you have a deflated baloon, draw two dots on it 1cm apart then blow the balloon up...the two dots will expand apart from each other but they are not expanding from a single point, but every point. Its the fabric of space that is expanding. It's also expanding faster than the speed of light. We know this due to the 'red shift' when observing far away galaxies. This is a result of the light waves being 'stretched', in that the photons that make up light on their merry way from a far away galaxy to our eyes end up having the space in which they travel expand before they can get to their destination. Now, i think that the galaxies that are furthest away are expanding away faster than those closest...so andromeda (our nearest galaxy) is not expanding away faster than speed of light but the further away ones are because the further away they are from you the faster the space expands. Now, the real head f##k is that this is the same from every vantage point in the universe so space is expanding faster the further away everything is away from everything...i think. It has something to do with the universe having to be homogenous from everywhere...space expansion must equal itself out, like how if you have a really big stick, you point it away from you and turn, the end of the stick closest to you is travelling slowly, yet the end of the stick furthest away from you is travelling really fast in 'space' in comparison. I thnk thats how it was explained to me

So are we expanding? Getting fatter? No, apparently not. The gravitational forces that bind us on an atomic level are significantly stronger than the expansion of space. This is the same for galaxies/solar systems themselves, they are not expaning from within themselves but the space around them is. Bit convenient that i always think.

The reason why galaxies collide is that as well as the previous point that gravitational forces are much stronger than that of the expanding universe (think of it in the same way a fridge magnet can overcome the earths gravitational pull - gravity holds the bloody moon where it is but a fridge magnet can overcome that force!) and all matter in the universe is attracted to each other by gravity, but also galaxies are moving around in space freely anyway, like a bit of flotsom on water, so at some point its always going to happen that galaxies will collide.

I have no idea if any of that made sense...i just started typing and got carried away

This is pretty much correct except (if you add the nimic correction). In fact I think that the scientists now are saying that the universe is really expanding faster than the speed of light, though I don't know how they have measured it. For a start, we can't see the light coming from those galaxies because that light won't come here. What they think for sure though, is that since 8 bilions or so years, the universe started expanding faster, when in theory it should have started shrinking.

Which sends us to the bolded part. It seems that what you said is true of course, but not forever. The so-called dark energy (which we don't know nothing about) is the reason why universe is expanding, but interesting with the expansion of universe, the amount of dark energy is increasing. So, after a few billion years (maybe more) the force that universe expands will become stronger than the dark matter force (already there is more dark energy than dark matter) which will make galaxies unstable so they won't rotate around their suppermassive black hole. Knowing that dark energy will again continue increasing, after that it will become stronger than the force of gravity which makes stars and planets to stay together, after than it will become stronger than the weak force which means that the electrons won't rotate around the atom's nucleus and finally it will surprass even the strong force which means that there won't be more atoms at all. And it will still continue increasing and increasing. If we think of it as a limit of time, and we send the time to infinite, then ultimatelly everything will go to zero which means that we'll have only a massive 'ocean' of dark energy.

The biggest problem here is that we already don't know anything about dark energy (we now know quite a few things about dark matter but we are newbies when it comes to it's 'opponent') and it's a bit ironical considering that our universe is made for more than 70% from it. The other strange thing is that it seems that there is an almost infinite source of dark energy and it is continue increasing (or being created/born) all the time. feck knows why but the God surely made a bug in his giant program. He better start debugiind it sooner than later, or we're fecked!

 

[Dracula]

This is pretty much correct except (if you add the nimic correction). In fact I think that the scientists now are saying that the universe is really expanding faster than the speed of light, though I don't know how they have measured it. For a start, we can't see the light coming from those galaxies because that light won't come here. What they think for sure though, is that since 8 bilions or so years, the universe started expanding faster, when in theory it should have started shrinking.

Which sends us to the bolded part. It seems that what you said is true of course, but not forever. The so-called dark energy (which we don't know nothing about) is the reason why universe is expanding, but interesting with the expansion of universe, the amount of dark energy is increasing. So, after a few billion years (maybe more) the force that universe expands will become stronger than the dark matter force (already there is more dark energy than dark matter) which will make galaxies unstable so they won't rotate around their suppermassive black hole. Knowing that dark energy will again continue increasing, after that it will become stronger than the force of gravity which makes stars and planets to stay together, after than it will become stronger than the weak force which means that the electrons won't rotate around the atom's nucleus and finally it will surprass even the strong force which means that there won't be more atoms at all. And it will still continue increasing and increasing. If we think of it as a limit of time, and we send the time to infinite, then ultimatelly everything will go to zero which means that we'll have only a massive 'ocean' of dark energy.

The biggest problem here is that we already don't know anything about dark energy (we now know quite a few things about dark matter but we are newbies when it comes to it's 'opponent') and it's a bit ironical considering that our universe is made for more than 70% from it. The other strange thing is that it seems that there is an almost infinite source of dark energy and it is continue increasing (or being created/born) all the time. feck knows why but the God surely made a bug in his giant program. He better start debugiind it sooner than later, or we're fecked!

One thing I don't understand about dark energy...I know the universe is made up of matter, dark matter and dark energy. It's the repulsive force of the dark energy that makes the universe expand. But what about 'Normal' energy like kinetic, potential, heat etc .. is that in the 'matter' category of what universe is made of?
If matter and energy are interchangeable would it be possible to transform dark energy into dark matter?
You say, if there is a good that his program is flawed, but perhaps this is the way universes are created by expanding then imploding, then s big bang... cyclical

 

[Ubik]

At the current rate of expansion the universe won't implode, it'll just carry on getting bigger whilst all the stars burn out. Will be a bit of a dull end, really.

 

[Revan]

One thing I don't understand about dark energy...I know the universe is made up of matter, dark matter and dark energy. It's the repulsive force of the dark energy that makes the universe expand. But what about 'Normal' energy like kinetic, potential, heat etc .. is that in the 'matter' category of what universe is made of?
If matter and energy are interchangeable would it be possible to transform dark energy into dark matter?
You say, if there is a good that his program is flawed, but perhaps this is the way universes are created by expanding then imploding, then s big bang... cyclical

The God part was a joke, I don't believe in anything like that.

Matter and energy are interchangable as have been shown by Einstein famous formula and various experiments. Energy counts in that what we call matter. Same about neutrinos which strangely enough add as much matter/energy to universe as all the stars together.

Dark matter and dark energy on the other hand... Don't be fooled by the name, there isn't such a relation between them as by matter and energy. The name dark comes because they are dark for us in such a way that we don't understand them and they don't 'interfere' with us. We can detect their effects, but not them (though theoriticcally we may create dark matter in the future, possibly though it will be extremely hard to detect it, much harder than neutrinos and we still have difficulties to detect them) while we don't know nothing about the nature of dark energy. In fact we don't know that such a thing really exists, but we know that universe 'wrongly' is getting increased and for that it needs to be a big source of energy which we have called 'dark energy'. I think that it wasn't the right name because people may think that there exists a relation between it and dark matter (similar to the relation between matter and energy) but as we know, there isn't such a relation. In fact we can say that they are two titans fighting for supremacy. Without dark matter there wouldn't be galaxies (and ultimatelly we wouldn't be here discussing it) and dark matter is the reason why galaxies are stable (it looks that galaxies are in the middle of an ocean of dark matter). On the other side, dark energy is in a way the opposite of it, it will be the reason why galaxies (and everything inside them) won't exist.

Universe doesn't seem that is planning to shrink. As I said in the previous post, scientists believe that it will expand 'forever' which was a bit strange when they realized it and ultimatelly made them think that there is a form of mysterious ever-increasing near infinite amount of energy that is making universe to increase.

 

[nimic]

Here's an interesting (and slightly sad) consequence of the expansion of space. In many, many billions of years (perhaps trillions), there will still be stars, and there will still be habitable planets where life can form. There are fundamental facts about the universe that any such life form, even when reaching sufficiently high technological levels, will never be able to discover. They will likely never be able to find out about the big bang, for one. The background radiation that is still here today, and that has helped point us towards it, will by then be undetectable. Also, everything will tell them that the entire universe consists of their galaxy, and that there is nothing else. They will not have knowledge of any other galaxies, since those will either have merged with their own galaxy or be expanding so fast (and have been for so long) that the light from those galaxies will never reach them.

So, to paraphrase Lawrence Krauss, they will arrive at a conclusion about the origins of the universe that is the best possible scientific explanation they can come up with, and that will still be utterly wrong.

That is, unless there are some other obvious signs that is unrelated to the expansion of space that we just haven't discovered yet.

 

[nimic]

(it looks that galaxies are in the middle of an ocean of dark matter)..

Furthermore, we have discovered that most of the mass within galaxies lies where there are no stars.

 

[Revan]

Here's an interesting (and slightly sad) consequence of the expansion of space. In many, many billions of years (perhaps trillions), there will still be stars, and there will still be habitable planets where life can form. There are fundamental facts about the universe that any such life form, even when reaching sufficiently high technological levels, will never be able to discover. They will likely never be able to find out about the big bang, for one. The background radiation that is still here today, and that has helped point us towards it, will by then be undetectable. Also, everything will tell them that the entire universe consists of their galaxy, and that there is nothing else. They will not have knowledge of any other galaxies, since those will either have merged with their own galaxy or be expanding so fast (and have been for so long) that the light from those galaxies will never reach them.

So, to paraphrase Lawrence Krauss, they will arrive at a conclusion about the origins of the universe that is the best possible scientific explanation they can come up with, and that will still be utterly wrong.

That is, unless there are some other obvious signs that is unrelated to the expansion of space that we just haven't discovered yet.

Never though about that, but you're very likely right. If the universe expands so much than every galaxy will be unreachable by another galaxy, then the inhabitants of that galaxy will think that the entire universe is made of that galaxy which as you said is wrong. In fact, what if our entire universe is just a big 'galaxy' inside of a giant universe which has been expanding for much longer? Of course a stupid question, but in a way that will be what they'll think.

Furthermore, we have discovered that most of the mass within galaxies lies where there are no stars.

Yep, that's correct. Which makes us think that there is something there, which while undetectable it clearly has gravity (or shrinks the spacetime depending if you want to think by theory of gravity or general theory of relativity).

 

[hungrywing]

At the current rate of expansion the universe won't implode, it'll just carry on getting bigger whilst all the stars burn out. Will be a bit of a dull end, really.

Always hope there is.

 

[Will Absolute]

Here's an interesting (and slightly sad) consequence of the expansion of space. In many, many billions of years (perhaps trillions), there will still be stars, and there will still be habitable planets where life can form. There are fundamental facts about the universe that any such life form, even when reaching sufficiently high technological levels, will never be able to discover. They will likely never be able to find out about the big bang, for one. The background radiation that is still here today, and that has helped point us towards it, will by then be undetectable. Also, everything will tell them that the entire universe consists of their galaxy, and that there is nothing else. They will not have knowledge of any other galaxies, since those will either have merged with their own galaxy or be expanding so fast (and have been for so long) that the light from those galaxies will never reach them.

So, to paraphrase Lawrence Krauss, they will arrive at a conclusion about the origins of the universe that is the best possible scientific explanation they can come up with, and that will still be utterly wrong.

That is, unless there are some other obvious signs that is unrelated to the expansion of space that we just haven't discovered yet.

We may well be in a similar position ourselves. The ultimate reality of the Universe (Universes) may be forever hidden from us.

 

[Maagge]

Here's an interesting (and slightly sad) consequence of the expansion of space. In many, many billions of years (perhaps trillions), there will still be stars, and there will still be habitable planets where life can form. There are fundamental facts about the universe that any such life form, even when reaching sufficiently high technological levels, will never be able to discover. They will likely never be able to find out about the big bang, for one. The background radiation that is still here today, and that has helped point us towards it, will by then be undetectable. Also, everything will tell them that the entire universe consists of their galaxy, and that there is nothing else. They will not have knowledge of any other galaxies, since those will either have merged with their own galaxy or be expanding so fast (and have been for so long) that the light from those galaxies will never reach them.

So, to paraphrase Lawrence Krauss, they will arrive at a conclusion about the origins of the universe that is the best possible scientific explanation they can come up with, and that will still be utterly wrong.

That is, unless there are some other obvious signs that is unrelated to the expansion of space that we just haven't discovered yet.

Very interesting. I never thought about that actually.

Never though about that, but you're very likely right. If the universe expands so much than every galaxy will be unreachable by another galaxy, then the inhabitants of that galaxy will think that the entire universe is made of that galaxy which as you said is wrong. In fact, what if our entire universe is just a big 'galaxy' inside of a giant universe which has been expanding for much longer? Of course a stupid question, but in a way that will be what they'll think.



Yep, that's correct. Which makes us think that there is something there, which while undetectable it clearly has gravity (or shrinks the spacetime depending if you want to think by theory of gravity or general theory of relativity).

I don't think you should call that a stupid question though. If that was indeed the case we'd have no way of knowing it and thus would feel pretty damn offended being called stupid for it.
It was the first thing that sprung to my mind as well when I read niMic's post.

 

[Ubik]

Always hope there is.

I think the expansion would have to speed up for that to happen, though. We're headed towards heat-death

I like the multi-verse theory myself.

 

[nimic]

We may well be in a similar position ourselves. The ultimate reality of the Universe (Universes) may be forever hidden from us.

Ultimately, yeah. At least we're fairly sure about the big bang, though.

 

[Revan]

I think the expansion would have to speed up for that to happen, though. We're headed towards heat-death

I like the multi-verse theory myself.

These theories aren't mutually exclusive. One is for our universe, the other for multiverse which containst our universe.

Always hope there is.

Hope for?

 

[Revan]

Ultimately, yeah. At least we're fairly sure about the big bang, though.

Maybe in reality the big bang was a collision between some particles in a LHC in the real universe

 

[SteveJ]

Five Billion Years of Solitude: The Search for Life Among the Stars ~

Astronomy is enjoying a golden age, but why does the search for intelligent life outside our galaxy matter – and will we ever move off-planet?:

http://www.theguardian.com/books/2013/nov/21/five-billion-years-solitude-lee-billings-review

 

[Maroon Lucifer]

Neil deGrasse Tyson
New video: If we live in an expanding universe, how can galaxies collide with each other? Watch astrophysicist Neil deGrasse Tyson ease Eugene Mirman’s concerns about our Milky Way galaxy’s impending collision with the Andromeda Galaxy… in about 6-8 billion years:





Funny that the exact question I posted on the top of this page, was being answered by NdGT on my facebook timeline

 

[Dracula]

I was listening to some astronomy lady on radio today. The dj was asking her about time dilation with speed- that the faster you go, time moves slower (relative to other slower moving person). So the dj asked if one person was planted on a comet travelling thousands of miles per hour for a year, and then planted back on earth, would they be slightly younger than someone else who didn't travel. Now she went on to say this was the 'twin paradox' but that there is no paradox in reality because although the person would experience time slower when going fast when they decelerate they would catch up the time missed so the Answer was no the person once got back to earth would not be younger.
Now, I was under the impression this was incorrect. This means that time would speed up with deceleration, which I can understand but surely it wouldn't speed up to the point to make time equal to when you left with someone on earth... Can someone explain this to me?

 

[hungrywing]

She's wrong. You're right.

What she's talking about happens only during the "turnaround" of the traveling party. While she's turning around, a gravitational potential applies - she's pressed into the spaceship floor just as if she were 'on earth' - and for that interval it's as if she's on earth and the other party (the one actually on earth) is in fact way way out there away from this gravitational well. During this turnaround, his clocks will 'speed up' from her point of view. This does 'cut into' the final calculations, but it's minuscule compared to the General Relativity time dilation she's been experiencing during her near-light-speed traveling.

A couple of minor notes: develop the habit of never separating space and time. They're different dimensions of a single coordinate system. Time itself doesn't "speed up" or "slow down". Mass travels a longer path through the local time dimension the closer it gets to C.

 

[Ubik]

Looks like the Sun has kerploded comet Ison

 

[Revan]

Looks like the Sun has kerploded comet Ison

Seems so. I was excited to see it.

 

[Dracula]

Looks like the Sun has kerploded comet Ison

Seems so. I was excited to see it.

No, it may, or most of it may have survived. ..

 

[Ubik]

Better news indeed, although according to the beeb it's only a small part that may have survived. Have to give it a couple of days to see what happens.

 

[MajorTom]

 

[Dracula]

That's amazing gif. But makes me wonder if that camera saw it come out the other side... Where is it now?

 

[Ubik]

From what I've read, it seems what came out the other side wasn't so much the comet as the relic of the comet, it got torn apart and that stuff's just debris.

 

[17Larsson]

Lawrence Krauss on the future of the Universe
http://www.smithsonianmag.com/scien...he-Future-of-the-Universe-Hold-236106251.html

 

[cesc's_mullet]

This stuff just blows my mind. I can't truly fathom just how huge some of those larger planets a galaxies are, let alone the universe as a whole.