Space

[Lance Uppercut]

Depends. If the universe was created by the big bang then for every action there is an equal or opposite reaction. The opposite reaction to the big bang is the big crunch. Then again depending of the amount of dark matter, then the universe can expand infinitely.

lol - Newtonian physics don't work on a quantum level.

It even had Einstein buggered. That's why we're still searching for a Grand Unified Theory.

 

[AndSmithMustScore]

the final frontier..................these are the voyages of the................oops sorry

 

[Copernicus]

It's a hard concept to wrap the mind around - sometimes I wonder whether there is something outside the boundaries of the universe, but then I get a headache and wonder why I did that.

It's an incredible notion, though. I am quite certain we wont be the only advanced lifeform out there, but with the distances involved, chances are we will never know.

 

[Tony_Clifton]

If we are just a computer program then the way to find this out can be found at the microscopic level. If we look close enough it might start to break down, some areas of quantum physics have unsolved discrepencies. Of course it would be easier just to look for the pixels.

 

[The_Eagles]

its mindboggling times like these I turn to the Bible

 

[pinkus maximus]

i ahte thinking about this stuff. it just hurts my brain

 

[Rowie09]

lol - Newtonian physics don't work on a quantum level.

It even had Einstein buggered. That's why we're still searching for a Grand Unified Theory.

Laymans terms. Just like saying "what goes up must come down". Didnt mean to apply newtons law literally, just as a way of explaining the big crunch theory.

 

[Kangaroopit]

Does it just keep going forever?

Surely you get to the end somewhere...how can something keep going forever?

What the hell is space?

For all we know there could be a million other planets just like Earth, with people just like us, it's ridiculous.

What do you think?

It's difficult to know whether space is infinite in extent. All we can say for now is that it's very, very big. It appears to be 13.7bn years old (I say appears because if inflationary theory is right, it is much older and perhaps infinite in age), so we can only see things that are within about 13bn lightyears from us, because that's how long the light has had to travel. This region is called the visible universe.

For various, slightly technical reasons, it observationally appears to be the case that the full universe is vastly huge compared to the visible universe, and a lot of theories would also point in that direction. Particularly Inflation, which would have many, many regions of space with different physical laws/constants, each region probably a lot bigger than the visible universe. Alan Guth, who originally put the theory forward, estimated the full universe as at least 10^23 times the size of the visible bit, but I'm not sure how he came to that.

Personally, I don't like the idea of an infinite universe, but it could well be.

In terms of reaching an end... I'd be very confident in saying that wouldn't happen. If the universe isn't infinite, then we would expect it to be shaped as the surface of a 4-dimensional analogue of a sphere. This is difficult to visualise, but the point is that on the surface of a sphere, if you keep travelling, you get back to where you started. The same would be true of space. The universe would be finite but unbounded.

As for the question of what space is, that is very difficult, and the answer is not yet known. Our view of space has changed a lot since the days of Newton, when space was considered just an arena for things to happen in. Now it's considered dynamic, interacting with the matter in the space, and fundamentally tied up with time. Maybe if we can tie general relativity in with quantum we'll get a better understanding, but for now, that's a toughie.

Guesses about how common life is are enormously speculative. I'd like to think that it is reasonably common on planets where it can exist, but I am sure that there is life out there, and because of the vastness of the universe, there is a lot of it. In fact, the only reasons I can think of for doubting the existence of extra-terrestrial life would be religious ones. However, the United Federation of Planets is probably precluded by the enormous distances involved, definitely under our current understanding of physics. But it would be nice to know that we weren't alone.

Yes the universe is still expanding meaning there are no defined boundaries as yet, as it is still getting bigger. I think it is the Big Crunch theory that states that eventually, gravity will drag back the expansion of the universe upon itself?

Almost certainly won't happen. I say that because of the surprising fact that the vacuum has a density. In fact, 73% of the density of the universe is contributed by the vacuum (along with 4% from everyday matter and 23% from dark matter). This has the effect of accelerating the expansion of the universe. It's hard to see the universe collapsing under gravity when the expansion is accelerating. Short of bringing in very speculative theories about the end of the universe, the most likely prediction is for the distant future to be very cold, with all the stars burnt out, infinitely far apart from each other. This is the Big Freeze.

Thermodynamic paradox states that for the universe to be infinite it has to be infinitely old. We know that due to big bang theory, the universe is finitely old therfore finite, yet expanding.

Meh. Imagine the distances in the universe being multiplied by a scale factor. Today the scale factor might be 1. In the past it was smaller. At the big bang it was 0. People don't seem to have much problem with the idea of an infinite universe coming from a singularity. It's a bit academic anyway, since our current laws of physics don't work at the big bang. Quantum and GR disagree. This doesn't usually matter, but it would near the big bang. We can only push our theories back as far as 10^-43 seconds after the bang. Until the two theories can be reconciled, people don't talk much about what happened before that.

And we don't know the universe to have a finite age. A lot of big problems in astrophysics can be solved by supposing that the universe spent an enormous amount of time lingering, prior to the sudden expansion 13.7bn years ago.

In other news, I've just finished my masters in astrophysics. Hazzah!

 

[Rowie09]

It's difficult to know whether space is infinite in extent. All we can say for now is that it's very, very big. It appears to be 13.7bn years old (I say appears because if inflationary theory is right, it is much older and perhaps infinite in age), so we can only see things that are within about 13bn lightyears from us, because that's how long the light has had to travel. This region is called the visible universe.

For various, slightly technical reasons, it observationally appears to be the case that the full universe is vastly huge compared to the visible universe, and a lot of theories would also point in that direction. Particularly Inflation, which would have many, many regions of space with different physical laws/constants, each region probably a lot bigger than the visible universe. Alan Guth, who originally put the theory forward, estimated the full universe as at least 10^23 times the size of the visible bit, but I'm not sure how he came to that.

Personally, I don't like the idea of an infinite universe, but it could well be.

In terms of reaching an end... I'd be very confident in saying that wouldn't happen. If the universe isn't infinite, then we would expect it to be shaped as the surface of a 4-dimensional analogue of a sphere. This is difficult to visualise, but the point is that on the surface of a sphere, if you keep travelling, you get back to where you started. The same would be true of space. The universe would be finite but unbounded.

As for the question of what space is, that is very difficult, and the answer is not yet known. Our view of space has changed a lot since the days of Newton, when space was considered just an arena for things to happen in. Now it's considered dynamic, interacting with the matter in the space, and fundamentally tied up with time. Maybe if we can tie general relativity in with quantum we'll get a better understanding, but for now, that's a toughie.

Guesses about how common life is are enormously speculative. I'd like to think that it is reasonably common on planets where it can exist, but I am sure that there is life out there, and because of the vastness of the universe, there is a lot of it. In fact, the only reasons I can think of for doubting the existence of extra-terrestrial life would be religious ones. However, the United Federation of Planets is probably precluded by the enormous distances involved, definitely under our current understanding of physics. But it would be nice to know that we weren't alone.



Almost certainly won't happen. I say that because of the surprising fact that the vacuum has a density. In fact, 73% of the density of the universe is contributed by the vacuum (along with 4% from everyday matter and 23% from dark matter). This has the effect of accelerating the expansion of the universe. It's hard to see the universe collapsing under gravity when the expansion is accelerating. Short of bringing in very speculative theories about the end of the universe, the most likely prediction is for the distant future to be very cold, with all the stars burnt out, infinitely far apart from each other. This is the Big Freeze.



Meh. Imagine the distances in the universe being multiplied by a scale factor. Today the scale factor might be 1. In the past it was smaller. At the big bang it was 0. People don't seem to have much problem with the idea of an infinite universe coming from a singularity. It's a bit academic anyway, since our current laws of physics don't work at the big bang. Quantum and GR disagree. This doesn't usually matter, but it would near the big bang. We can only push our theories back as far as 10^-43 seconds after the bang. Until the two theories can be reconciled, people don't talk much about what happened before that.

And we don't know the universe to have a finite age. A lot of big problems in astrophysics can be solved by supposing that the universe spent an enormous amount of time lingering, prior to the sudden expansion 13.7bn years ago.

In other news, I've just finished my masters in astrophysics. Hazzah!

Thanks for ruining a hearty thread Mr Hawking.

just kidding

 

[Kangaroopit]

Thanks for ruining a hearty thread Mr Hawking.

just kidding

Sorry about that. I'll try not to do that again, but it's not often that threads on astrophysics come up, so I jumped on it.

In summary: Space - Big.

 

[Rowie09]

Sorry about that. I'll try not to do that again, but it's not often that threads on astrophysics come up, so I jumped on it.

In summary: Space - Big.

Haha. I actually enjoyed it thouroughly. Impressing strangers on a forum is just one of the perks of having a masters in astrophysics i guess

 

[Cap]

Sorry about that. I'll try not to do that again, but it's not often that threads on astrophysics come up, so I jumped on it.

In summary: Space - Big.

all i can say is wow

was does a masters in astrophysics get you ??

when will you be building star ships that can do Warp speed

 

[TigerCraig]

was does a masters in astrophysics get you ??

Staff rates on Happy Meals

 

[Higgs Boson]

It's difficult to know whether space is infinite in extent. All we can say for now is that it's very, very big.

...

In other news, I've just finished my masters in astrophysics. Hazzah!

Out of interest, have you ever read any Stephen Baxter? If so, I'd love to hear your opinion as someone who actually knows what they are on about with these sorts of things. Personally, I think some of the concepts he writes about are amazing.

 

[deeman12]

Depends on whether religious or not, i dont think that there is other life forms like aliens and that.

 

[Lance Uppercut]

Out of interest, have you ever read any Stephen Baxter? If so, I'd love to hear your opinion as someone who actually knows what they are on about with these sorts of things. Personally, I think some of the concepts he writes about are amazing.

teh new one is ####ing awesome btw

 

[Aussie Assault]

Space is all a conspiracy. The Yanks made it up. There is no such thing

But seriously, how do scientists know what they are looking for? Why do other life forms out there have to have the same set up as us? They may require hotter/colder temperatures, with or without oxygen. How do we know that out 5 senses can even see them, or hear them etc?

Too many questions for me, and I agree with Pinkus Maximus. Just hurts to try and grasp it all!

 

[Higgs Boson]

teh new one is ####ing awesome btw

Finished it yet?

 

[Kangaroopit]

all i can say is wow

was does a masters in astrophysics get you ??

when will you be building star ships that can do Warp speed

Erm... it gets a good reaction from people when I tell them I study astrophysics.

Warp speed's tricky. It involves getting around the fact that you can't travel faster than light by dragging the space you're in with you, so that you aren't travelling faster than light in your local space, but your local space is going faster than light. To do that, they think you'd need masses of negative energy. Like, several times the mass of the Sun's worth of negative energy. We don't really know how to get negative energy, so we're a bit stumped there.

Out of interest, have you ever read any Stephen Baxter? If so, I'd love to hear your opinion as someone who actually knows what they are on about with these sorts of things. Personally, I think some of the concepts he writes about are amazing.

Sorry, I haven't read much science fiction, except for 2001 and Dune. I'm quite proud that I'm one of the few people on my course who can talk for longer about sport than Star Trek.

Depends on whether religious or not, i dont think that there is other life forms like aliens and that.

I've for a while maintained that discovery of aliens would be very difficult for a lot of organised religions. This was something that occurred to St Augustine (I think, might have been Aquinas) and Thomas Paine, who drew opposite conclusions from the problem. Augustine reasoned that since aliens would need redemption, and since Christ died only once, on Earth, therefore there were no aliens. Paine felt that the existence of aliens was obviously true, therefore there was no crucifixion. I think Islam might also struggle, unless all aliens have their own version of the Qur'an. Not necessarily the same, since Shari'ah Law might be different for them than for us.

Personally, I think it would be absurd and arrogant to say that we are the only intelligent life in the universe, a hangover from the religious view that we are somehow special, with the universe created for our benefit.

Space is all a conspiracy. The Yanks made it up. There is no such thing

But seriously, how do scientists know what they are looking for? Why do other life forms out there have to have the same set up as us? They may require hotter/colder temperatures, with or without oxygen. How do we know that out 5 senses can even see them, or hear them etc?

Too many questions for me, and I agree with Pinkus Maximus. Just hurts to try and grasp it all!

Good question. Astrobiology is a slightly vague subject made out of astrophysics, biology and geology. It's almost impossible to second guess nature on what's possible, so all we can really do is look for things that are familiar to us from what happens here. We don't know of any way for life more complex than bacteria to exist other than the way it does here (burning fuel with oxygen to release energy) and we think that having liquid water helps. So we look for Earth-sized planets that are the right distance from their star for liquid water to exist on the surface. Having a big planet like Jupiter further out in the same system is also useful, as it sweeps up stray asteroids that otherwise might cause mass extinctions.

If eukaryotic, multicellular life (ie including plants and animals) or something like it, arises, there are some respects in which we can reasonably expect it to continue. Eyes are thought to have evolved somewhere between 40 and 60 different times, independently, on Earth, so there's a good chance that aliens would have them too. Some things are just useful. Ultimately, I think we're looking for intelligent life, someone for us to talk to. There might be very different forms of life out there, but it's harder to know what to look for there.

 

[BomberGal]

But seriously, how do scientists know what they are looking for? Why do other life forms out there have to have the same set up as us? They may require hotter/colder temperatures, with or without oxygen. How do we know that out 5 senses can even see them, or hear them etc?

They don't necessarily require the same setup, but there will be basic things required for life. (Biochemist here.)

They don't have to have water, but another life system is going to require some universal solvent, otherwise molecular interactions are not going to happen. They are going to require certain gases for atmospheric & environmental interaction, and protection from, say, their sun. To build cells/bodies/structures, life is going to require some form of polymer - we have DNA, proteins, carbohydrates - there it could be different, but structural molecules should still be present. It's perfectly possible to have higher or colder temperatures - there are creatures on earth called extremophiles, which, as the name suggests, like extreme conditions. Granted, many of these are unicellular, but you never know what the conditions on another planet will allow to evolve. Physics, chemistry, kinetics, thermodynamics...these will only allow certain ways for life to evolve. So even though alien life may be drastically different to what we know here on earth, we should still expect it within certain parameters.

We should still be able to see them, at least, as they are going to be made of molecules! The rest of the universe still has to abide by the same laws of physics that life here on earth does, which is why we can expect life to be within certain parameters. That said, you wouldn't expect them to look the same, because evolution will be unique - selection pressures will be entirely different. Presuming they'd evolved beyond simple cells/structures, then, for example, they'd probably have some form of light sensor, but whether this is analogous to our own eye or any eyes we see on earth...we wouldn't know until we saw it.

 

[Higgs Boson]

We should still be able to see them, at least, as they are going to be made of molecules! The rest of the universe still has to abide by the same laws of physics that life here on earth does, which is why we can expect life to be within certain parameters.

Hmmm, I don't know about that... what about, for example, close to a singularity, where space-time is seriously warped?

 

[BomberGal]

Hmmm, I don't know about that... what about, for example, close to a singularity, where space-time is seriously warped?

OK, I'm no physicist, so excuse any stupid comments I may make here. But would you really expect life to evolve next to a black hole? I wouldn't. Wouldn't be enough light or heat available surely.

 

[johnnyhoward]

Space stops after Pluto. Bookmark it.

I'll be back in 10,420 AD to pwn you.

 

[Higgs Boson]

OK, I'm no physicist, so excuse any stupid comments I may make here. But would you really expect life to evolve next to a black hole? I wouldn't. Wouldn't be enough light or heat available surely.

Probably, but I guess it depends on how you characterise life... if there is energy there, perhaps it's not inconceivable that something could make the most of that energy... who knows?

 

[Lance Uppercut]

Xelee