Space

[Dan26]

Wasn't the idea that the 5th dimension was something to do with probability from Mostly Harmless?

One thing that I deliberately didn't mention before is that the extra dimension in which space is curved is time. I thought that might confuse, and you don't really need to know that it is the case when you're trying to imagine curved space. Space and time aren't really seperate, but different aspects of the same thing.

As far as I know, there isn't a connection between parallel universes and extra dimensions. String theorists will claim that there are 10, 11 or 26 dimensions. I don't know how they reached those conclusions, but I do know that all the arguments for string theory are based on mathematical beauty. By all accounts string theory is startlingly elegant and beautiful, but that doesn't change the fact it is yet to produce a single experimental prediction, and that makes it quite contraversial. String theorists say that the extra dimensions are curled up in such a way that if you move even a very small amount in an extra direction you will return to where you started. It's like the universe being the surface of a hosepipe. If it's a thin hose, and you were looking at it from a distance, you might think it was just one dimensional, but actually there is a second dimension, you could go around the hose. String theorists think the universe is a bit like that, but with the extra dimensions being really tiny, so we don't see them.

Parallel universes seem to be brought up for two different reasons:

1. To explain the apparent fine tuning of the universe. There are physical constants that have to be set very specifically for the universe to be suitable for life. If you changed the strength of gravity, even to the fifteenth decimal place, then either the universe would have recollapsed after the Big Bang and formed a black hole or everything would have expanded forever and never formed stars and galaxies. Many people suggest that there are an infinite numer of universes, each with slightly different physical constants. It makes it seem less like luck that we are able to exist.

2. As a possible interpretation of quantum theory. It is claimed that there are myriad universes and that when something for which quantum effects are significant is measured, different universes will measure different things. That is an over-simplified and dulled down description of them, but they're worth reading about. I recommend The Fabric of Reality by David Deutsch. Though this interpretation is a minority viewpoint, it is a perfectly respectable one.

Interesting.

Do you know of any theories about the causality of the Big Bang? As in what prompted it? Does the Universe supposedly expand to such a point where it contracts and eventually starts all over again? Hence the Big Bang. The idea that before the Big Bang there was "nothing" no space, no time etc is an amazing thought beyond any humans' comprehension, and I'm of the belief that there is a scientific explanation for everything.

 

[Kangaroopit]

Interesting.

Do you know of any theories about the causality of the Big Bang? As in what prompted it? Does the Universe supposedly expand to such a point where it contracts and eventually starts all over again? Hence the Big Bang. The idea that before the Big Bang there was "nothing" no space, no time etc is an amazing thought beyond any humans' comprehension, and I'm of the belief that there is a scientific explanation for everything.

Noone knows what happened before the Big Bang, and most would be of the opinion that time didn't exist before the Big Bang. The question is often compared to asking what's North of the North Pole. Anyway, our known laws of physics break down close to the Big Bang, so these aren't matters that we can really address. Quantum theory and general relativity contradict each other, though neither has ever been tested and found incorrect. This is because normally quantum theory only applies to tiny things, and GR to big things. At the Big Bang, they would both have an effect, and we won't be able to describe it until someone can unify the two theories as different aspects of a more complete theory. The idea of time having a start is just something you get used to.

The cyclic theory of the universe, where it expands, contracts, repeats etc is very unlikely since the universe is accelerating in its expansion.

I'm pretty certain that science cannot explain everything by its methods. I don't think that everything is explainable by any methods. But everything that is explainable, I think is explainable by either mathematical, scientific or philosophical methods. I think that that last sentence was either a tautology, or a statement of what I consider to be the legitimate methods of explanation.

 

[Lance Uppercut]

what happens before the singularity is unknowable - we cannot know

 

[Bryceson]

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?

best post ive read on big footy

id be ****ed if i get what space is

 

[Dan26]

Here's a question for kangaroopit or anyone else who wants to give it a go.

It concerns the speed of light.

Now lets suppose a spaceship leaves the earth and orbits the earth at close to the speed of light. Let's say 250,000 Km, per second. The people in the spaceship are going around and around and around the earth for exactly a year. They all have watches on, so they know they have been orbiting the earth for exactly a year.

When they come home, we have all aged 50 years (Now the maths might mean we would have aged 20 years or, 12 years or 2 years or whatever, but lets suppose, for the sake of the exercise that we have all aged 50 years)

This would mean, that if I were to walk outside my house and "look" at the spaceship orbiting the earth, it would appear to be moving very slowly from my point of view. In fact, it would hardly appear to be moving. Right?

And if the people in the spaceship were to somehow "look" at us, as they were orbiting the earth at massive speed, they would see us moving extremely quickly. They would see 50 years passing by on Earth, whilst in their own time, only one year would have passed, right?

Okay, now the point being that an "observer," such as myself would observe the fast movng object moving slowly (according to me) because the 50 years of time that I spend watching the object, would be only one year for the people on the object moving at massive speed.

Okay, so imagine a 2-man 100 meter sprint between the worlds two fastest men - Asafa Powell,and Tyson Gay.

Asafa, has some NASA Nike's that enable him to run at 250,000 km per second. Tyson just has a standard pair of Reeboks. The starter fires the gun and they're off! Asafa comletes the 100 meters in a fraction of a second (to him). Tyson Gay runs it in exactly 10 seconds (to him), which means for me watching 10.0000000001 seconds elapsed.

So, for me watching, I see Tyson complete the race in 10.0000000001 seconds (of my time)

But, what I can't visualise, is how I would observe Asafa Powell. He must get to the finish line first, right? He is running at 250,000 km per second. But when I look at him, he is moving extremely slowly. In fact, we have all aged 10 minutes while watching Asafa complete the race. I aged only 10.0000000001 seconds whle watching Tyson Gay (who in HIS time did it in exactly 10 seconds)

So my question, is, if I was to observe such a race, how would it "look?" In fact if Asafa was moving at just under the speed of light, he would appear to hardly be moving. So if Tyson Gay was in the lane next to him running at normal speed, how would it "look" visually? How could I literally observe Asafa winning, when he would be moving so slowly?

How is it possible for me to have aged 10 minutes while watching Asafa take forever to get to the finish line, and age only 10.0000000001 seconds while watching Tyson, when Asafa was the one running at super massive speed? It doesn't make sense. Surely I have to observe Asafa getting there first? Yet, it would take him 10 whole minutes (of my time) to get there. So, if this race happened, what would we see? What would we literally see?

 

[Kangaroopit]

This thread seems to have turned from me answering questions, into my own private tutorial.

Here's a question for kangaroopit or anyone else who wants to give it a go.

It concerns the speed of light.

Now lets suppose a spaceship leaves the earth and orbits the earth at close to the speed of light. Let's say 250,000 Km, per second. The people in the spaceship are going around and around and around the earth for exactly a year. They all have watches on, so they know they have been orbiting the earth for exactly a year.

When they come home, we have all aged 50 years (Now the maths might mean we would have aged 20 years or, 12 years or 2 years or whatever, but lets suppose, for the sake of the exercise that we have all aged 50 years)

You've made it slightly complicated by saying that the spaceship is going in a circle, so they're accelerating, which changes things. If they were just going in a straight line, then we would age 1.81 years in the time that they would age 1.

To work out the factor by which their time slows down, and by which their lengths shorten, you take their speed, divide it by the speed of light, square that, subtract it from one, square root that and divide 1 by that number.

I've found this graph showing how that factor changes with speed. As you can see, the effect only becomes significant when you're very close to the speed of light:

This would mean, that if I were to walk outside my house and "look" at the spaceship orbiting the earth, it would appear to be moving very slowly from my point of view. In fact, it would hardly appear to be moving. Right?

And if the people in the spaceship were to somehow "look" at us, as they were orbiting the earth at massive speed, they would see us moving extremely quickly. They would see 50 years passing by on Earth, whilst in their own time, only one year would have passed, right?

Certainly if they were travelling in a straight line, then if you looked at them, and if they looked at you, you would both see each other as moving slowly. That's part of the magic. They could just as easily have said that it was you who was moving past them at 250000km/s, and you would be moving slowly. But as they're accelerating, things are different. I think you're right, but there might be something clever I've missed.

Okay, now the point being that an "observer," such as myself would observe the fast movng object moving slowly (according to me) because the 50 years of time that I spend watching the object, would be only one year for the people on the object moving at massive speed.

Okay, so imagine a 2-man 100 meter sprint between the worlds two fastest men - Asafa Powell,and Tyson Gay.

Asafa, has some NASA Nike's that enable him to run at 250,000 km per second. Tyson just has a standard pair of Reeboks. The starter fires the gun and they're off! Asafa comletes the 100 meters in a fraction of a second (to him). Tyson Gay runs it in exactly 10 seconds (to him), which means for me watching 10.0000000001 seconds elapsed.

So, for me watching, I see Tyson complete the race in 10.0000000001 seconds (of my time)

But, what I can't visualise, is how I would observe Asafa Powell. He must get to the finish line first, right? He is running at 250,000 km per second. But when I look at him, he is moving extremely slowly. In fact, we have all aged 10 minutes while watching Asafa complete the race. I aged only 10.0000000001 seconds whle watching Tyson Gay (who in HIS time did it in exactly 10 seconds)

So my question, is, if I was to observe such a race, how would it "look?" In fact if Asafa was moving at just under the speed of light, he would appear to hardly be moving. So if Tyson Gay was in the lane next to him running at normal speed, how would it "look" visually? How could I literally observe Asafa winning, when he would be moving so slowly?

If Asafa is running at 250000km/s, then you would definitely see him win. While he is running at that speed you could measure his pulse, say, as going at 1/1.81 of what he would measure it as.

From Asafa's point of view, he would think that the rest of the world was moving at 250000km/s past him, and it would both be moving slowly, and contracted along the direction that he is running (which is the other thing that happens). So he would see that he only has to run 100/1.81=55.3m, and if the track went past him at 250000km/s, he would think it took him 2.2*10^-7 seconds. You would think it took him 4*10-7 seconds to run 100m.




That might all sound complicated and full of internal contradictions, so with apologies to Paul Davies, I'm going to paraphrase an example that he gave in his popular science book, About Time, because he's already done all the maths, and the numbers are nice and round:

Suppose there are a pair of twins, Ann and Betty. Betty is going to go on a journey, leaving Earth in 2000, going to a star 8 lightyears away, and returning to Earth in 2020. She won't spend any time sightseeing, and for the sake of argument, we'll say she changes direction instantaneously just to keep the maths simple. She will travel at 240,000km/s. Dividing this by the speed of light gives 0.8, squaring give 0.64, subtracting from 1 give 0.36, and taking the square root of that give a factor of 0.6. Betty will therefore experience only 12 years (20*0.6).

If they have telescopes, and can watch each other over the journey, Betty could look back at Ann, and would think that Ann's clock is running at 0.6 times the speed of her own clock. But when she looks, she sees the clock moving even slower than that because of the Doppler effect. When Betty looks at Ann, she can't see what Ann is doing that instant, she can only see what she was doing some time ago because the light from Ann takes some time to reach Betty. After 1 hour's flight (as measured on Earth), Betty is 48 lightminutes away, so she sees Ann as she was 48 lightminutes earlier (as measured on Earth). Ann, looking at Betty, would likewise see Betty as being slowed down by both relativity and the Doppler effect.

The rocket reaches the star in 2010, but Ann won't actually see the rocket at the star till 2018, because of the time taken for the light to reach her. Betty, however, because of time dilation, thinks that she has covered the distance in just 6 years, rather than 10. So in 2018, Earth time, Ann would look at Betty's ship, and see the clock reading 2006. Over the past 18 years, Ann has been seeing Betty's clock running at just a third the rate of her own clock, or 20 minutes in one of Ann's hours. Ann is of course, perfectly capable of realising that part of the reason why the clock is going so slow is because of the Doppler effect, and can factor that out to deduce that Betty's clock has been running slow by a factor of 0.6, in agreement with the formula above. Ann deduces (but does not see) that Betty's clock has been running at 36 minutes to one of Ann's hours.

Before things go any further, it's worth mentioning that in relativity, simultaneity is subjective. You might think that two things happen at the same time, but I might disagree if I'm travelling at high speed relative to you.

Betty sees things differently, although she agrees that her clock measures 2006 when she reaches the star. From Ann's point of view on Earth, Betty's reaching the star happens in 2010, Earth time (though it isn't seen for another 8 years). But in 2010 Earth time, when Betty's reaching the star, Betty would be seeing light that left Earth in 2002. But as Betty's clock reads 2006, we see that for the past six of her years, she has also been looking at Ann's clock and seeing it as moving at only a third the rate of her own clock. This sounds like an inconsistency, but it all fits together. Ann and Betty both think that the other one is moving slower. Betty, like Ann, can deduce that Ann's clock must actually have been running at 0.6 times the rate of her own clock.

Betty turns round and comes home. Because she is approaching Earth, the Doppler effect is now making Ann appear to speed up. Ann will also see Betty as moving faster, because of the Doppler effect. We agreed that Ann sees Betty at the star in 2018, and that Betty returns in 2020, so Ann sees the whole return journey taking place over just two years. When Betty returns, her clock will read 2012. Ann will see Betty's clocking counting the 6 years from 2006 to 2012 in two years, so over that time, she sees Betty's clock as running 3 times faster than her own, Earth-bound clock. Ann can untangle the Doppler effect from the relativistic effect, and deduces that Betty's clock is still running at 0.6 the rate of her own clock, but is made to look faster because she is approaching Earth. That's what she expects, because Betty is still travelling at 0.8 times the speed of light.

As for what Betty sees on the return journey, remember that she arrived at the star at 2006 her time, and was then able to see Ann in 2002. Over the next six years, she will see Ann's clock go through 18 years to 2020. She will see Ann's clock as going three times faster than her own. Betty deduces that Ann's clock is really running at 0.6 times the rate of her own. In spite of the fact that each twin has reckoned the other's clock to be running slow, there is no contradiction. It all fits together. One thing I didn't mention is that because Betty sees the universe as contracting in the direction that she is travelling, she thinks that she only has to cover 8*0.6=4.8 lightyears. 4.8 lightyears in 6 years, as opposed to 8 lightyears in 10, means that she agrees with Ann about what speed she travelled at.

I hope you appreciate all of that. If you have any more long questions, feel free to take them to http://www.bautforum.com/questions-answers/ where there are plenty of people with too much time on their hands.

 

[Moonwatcher]

If a spaceship travels at 250 000km/s away from an observer we really do see it move at that speed. Similarly they look at us and say we are moving at such a speed away from them (only considering the linear motion kangaroo mentioned). As in Paul Davies example (i haven't read the summary here) a telescope pointed at the spaceship would reveal the occupant living in slow motion (neglecting Doppler shifts)but remember their ship is still speeding away at 250 000Km/s. The fact one ages more than the others(earthlings) is due to the accelerations the ship has to perform. It is at these stages the accelerated aging on earth appears.

This takes us to the runners.

To say someone runs at 250 000 Km/s means that you observe them running at that speed relative to you/track (This part need not be made more complicated).
The fastest runner finishes first and the slower runner finishes second.
The only interesting observation here is that the fast runner claims(quite correctly) that he finished the race in a much shorter time than recorded by stationary observer and that the track wasn't the 100 m it was advertised to be. The slower runner could also make these claims but at such a slow speed wouldn't have noticed anything.

If the experiment was long enough we would notice that the fast runner had not aged much, but we don't see the runner running at anything less than the 250 000 km/s measured. Edit as this would clearlly contradict our initial observation that he was traveling at that speed.

 

[Moonwatcher]

David Duetch and Paul Davies we have the same book collection kangaroopit

 

[Dan26]

Thanks for your reply Kangaroopit. What I am having trouble with, is this part.

If Asafa is running at 250000km/s, then you would definitely see him win. While he is running at that speed you could measure his pulse, say, as going at 1/1.81 of what he would measure it as.

From Asafa's point of view, he would think that the rest of the world was moving at 250000km/s past him, and it would both be moving slowly, and contracted along the direction that he is running (which is the other thing that happens). So he would see that he only has to run 100/1.81=55.3m, and if the track went past him at 250000km/s, he would think it took him 2.2*10^-7 seconds. You would think it took him 4*10-7 seconds to run 100m.

If, from Asafa's point of view, if he thinks the rest of the world is moving super-fast at 250,000km/s (as you said), how would it be moving slowly (as you said)? I am trying to picture exactly how it would literally look if I observed this race. And how it would literally look from Asafa's point of view.

And you say the length of the track contracts. So let's suppose he is running at 99.99999999999% of the speed of light. Would the track appear to be only an inch long, from his point of view?

 

[KingsCrow]

I have never been so confused in my life

 

[Kangaroopit]

If, from Asafa's point of view, if he thinks the rest of the world is moving super-fast at 250,000km/s (as you said), how would it be moving slowly (as you said)? I am trying to picture exactly how it would literally look if I observed this race. And how it would literally look from Asafa's point of view.

He would be aware that objects were moving past him at 250,000km/s, but if he could see a clock by the side of the racetrack, he would see it as moving slowly. There must be something clever that happens when he slows down which makes everything fit together again. Because Asafa is the one who is speeding up and slowing down, the whole thing should end with him agreeing that he was the one for whom time ran slowly.

And you say the length of the track contracts. So let's suppose he is running at 99.99999999999% of the speed of light. Would the track appear to be only an inch long, from his point of view?

Yes. He would think that he ran a shorter distance in a shorter time than you think he did, but you'd agree about how fast he went.

An even more extreme example, a photon of light would travel at the speed of light (a feat achievable because it has no mass, nothing with mass could go that fast). To a photon, any journey it makes would be instantaneous, and cover no distance. If a photon were somehow carrying a watch, it wouldn't be ticking, but that doesn't alter the fact that we see the photon as travelling at the speed of light.

Although something has occurred to me, which might also have occurred to you, and I'm not sure what the resolution is. Say Asafa puts a foot on the ground every 2 metres, then that would be every 2 metres as far as he's concerned. So I think that we'd measure them as more than 2m apart. Though while he was running, we'd think that he was contracted along the direction he was running in. I'm not sure how all this fits together.

Questions like that one usually involve being quite clever. For example I was once set a question where you've got someone running, carrying a pole horizontally, going so fast that the pole is contracted. He runs into a barn, and for a split-second before he slows down, it is possible to slam the barn doors behind him. When he stops, the pole expands to its proper length, which is longer than the barn, so it breaks the doors open again. But from his point of view, it was the barn that was contracting while his pole remained full length, so how was it possible to close the doors? The answer is that from his point of view, he runs into the far wall of the barn, but the back end of the poll keeps moving for a second (because it takes time for the momentum to travel back up the poll) and the barn doors can close briefly while the back end of the poll is still moving forward before it is pushed back out by the force from the front end of the poll. Everyone agrees that the doors were closed for a while, but the man with the poll would think that the front end of the poll had already hit the far wall by the time the doors closed. Everyone always agrees whether or not an event took place, but they might disagree about how long things took, distances involved, and whether or not things happened simultaneously.

This is where I admit that though I have a Masters in Astrophysics, I'm not planning on going any further in academia, and am about to go travelling before finding myself a job in the real world. You'd probably get more luck by asking these questions to the people on the other forum I mentioned, many of whom are pretty fluent in matters like these.

 

[Moonwatcher]

I have never been so confused in my life

Massie Vs Franklin?

 

[Moonwatcher]

Although something has occurred to me, which might also have occurred to you, and I'm not sure what the resolution is. Say Asafa puts a foot on the ground every 2 metres, then that would be every 2 metres as far as he's concerned. So I think that we'd measure them as more than 2m apart. Though while he was running, we'd think that he was contracted along the direction he was running in. I'm not sure how all this fits together.

The special relativity version of this question is simple. Assuming Asafa was always running at that constant speed then both Asafa and the stationary viewer see Asafa maintain a constant stride length it's just that they do not agree what that length is. Asafa measures shorter, quicker strides.

This can be seen if you consider the number of steps it takes to finish the race, which will be the same for both observers. To travel a shorter distance in a shorter time in the same number of steps leads to the conclusion that Asafa measures shorter strides.

Closing the barn door is a great question, and seeing as it a special relativity question their is no need to consider the pole stopping ie momentum. As you said kangaroopit it's really a matter of realising that to events are not simultaneous from different observers traveling relative to each other. From the runners point of view the front of the pole reaches the back of the shed before the back of the pole reaches the front of the shed. In the barns rest frame it is possible to find a speed for the runner such that the two events front of pole at end of barn and the back of the pole reaching the front of the barn are simultaneous.

 

[Moonwatcher]

Closer to the OP. Sometimes i wonder what the universe exists in. Clearly the answer is nothing as the universe is everything. Also considering we can be pretty sure this universe exists, then i come to the conclusion that if one universe can come into existence from nothing then so could/should an infinite number of universes. On top of this i believe in an infinite number of bubble universes and the quantum multiverse, making my universe pretty complicated.

PS. Moonwatcher proudly joins the exclusive 24 posts club

 

[Marklar_33]

What I am understanding from the Asafa theory is that because he is travelling at nearly the speed of light, it would always take longer for light to catch up to him from behind, therefore everything seems slower... but if he were to be watching a clock both ahead and behind, would one be moving much faster than the other?

As for my opinion of space, it was said earlier that time having a beginning is something you get used to... I do not think I could EVER comprehend that. There has to be a certain "time" where everything lay dormant before the Big Bang... and as for the size of the universe, unless there are other universes bordering our own, it must go on and on... what can be external of our universe if its not another universe... there just cant be a wall, surely?

I would approximate that once a week I think about this, and once a week I end up stumped as too how any of it is possible... time had to start somewhere, but it had to be ticking before it started... and the universe must have boundaries, but there must be something beyond them!

 

[betterthanu]

This thread never ceases to both entertain and hurt my brain thanks largely to Kangaroopit.

 

[Moonwatcher]

Edit Response to Marklars statement.

That's the first step too understanding relativity. The most important part is everybody measures the speed of light to be the same regardless of whether you are trying to speed "away" from it or just "standing still". Instead of light taking longer to reach him he claims that in the equation speed of light = distance travelled by light / time, lightspeed is constant and distance and time vary to concur.

In terms of light sent to him from in front and behind from equal distance at the same time according to stationary observer ie (at rest with respect to the track). He runs toward the light in front of him and hence sees that light first!. Knowing that they were sent from equal distances and at the same speed, He assumes the light in front was sent earlier than the light from behind!!!. He does not agree with the stationary observer that the lights were sent simultaneously!!!. This point solves about every special relativity problem you will find.

This effect increases with distance.

Another Paul Davies example. If we walk towards the Andromeda Galaxy what a stationary person claims is today in that galaxy we perceive as yesterday!( we think that light was sent earlier).


Its interesting but not necessary to understand in everyday life.

 

[Moonwatcher]

What I am understanding from the Asafa theory is that because he is travelling at nearly the speed of light, it would always take longer for light to catch up to him from behind, therefore everything seems slower

Shorter answer ( I get carried away)
Your correct, also Asafa sees both clocks tick at the same rate, The difference is the clock in front reads a latter time (due to Asafa thinking light from it was sent earlier) It also appears bluer!! the clock behind actually looks redder and reads earlier time.

 

[Marklar_33]

Thanks Moon, Its comforting to know Im on the right track there! Still, a lot of the questions I have will remain unanswered, and thats the great thing about them I suppose... I will always be stumped by them, and no one answer will ever be right!

 

[Kangaroopit]

This thread never ceases to both entertain and hurt my brain thanks largely to Kangaroopit.

I do my best.