Astronomy & Space Exploration

[Prometheus]

 

[Buster15]

I've got so much to offer in these early pages but it's too long ago to respond now. C'est la vie.
I'm learning algebra from the ground up to help myself understand all this more intimately but the principals I've always been ok with.
And yea design doesnt mean god. There is no god. It is a great book, the holy grail of physics is to unify basically gravity with the 3 other forces to form a unified theory of the universe. The other 3, weak/strong nuclear force and electromagnetism have a force carrying particle associated with them but gravity hasnt. So they all work in newtonian and quantum physics but gravity is the odd one out as there is no force carrying particle. But black holes exist in the very tiny world of the plank scale as a singularity. This isnt resolved in my hero Hawkings books however.

As you will obviously know, there is much conjecture as to whether Gravity is actually a force at all.

I guess that when or if the graviton is discovered, that will give us the answer.

To my simple mind, it must be a force simply because it is believed that in the earliest minute fractions of a second after the big bang, all the forces were unified as a single force.

And as they began to separate, that gave rise to the cosmic inflation (theory).

Well done for learning algebra.

 

[giggs-beckham]

As you will obviously know, there is much conjecture as to whether Gravity is actually a force at all.

I guess that when or if the graviton is discovered, that will give us the answer.

To my simple mind, it must be a force simply because it is believed that in the earliest minute fractions of a second after the big bang, all the forces were unified as a single force.

And as they began to separate, that gave rise to the cosmic inflation (theory).

Well done for learning algebra.

Thanks. Ive always been a bit confused by gravity I get newtonian gravity GMm/r² and the basics of general relativity, gravitational lensing etc. But why do objects attract? Yes objects with mass bend spacetime and more massive objects bend it more but why does that bend or warped spacetime have the effect of attraction. Why does the apple fall. I can picture a moving object passing by earth having its path bent as it's really taking the shortest path across curved space architecture. Its geodisic path but why an object at rest starts moving.

I read it's to do with an objects 4 vector being affected by gravity. Which says I believe that all objects are moving at the speed of light all the time and c must be conserved. If at rest your 3 spacial velocities are 0 and your path through time is c. But if you're moving let's say very fast your time slows down doesnt it relatively. So your 4 velocity c is conserved. This makes sense to me as time dilation.

Now gravity causes time dilation as well as we know. Gravity slows your time down so to compensate you start moving/falling so c can be conserved and the closer to the centre of the earth you fall the stronger the gravity and the more your time is slowed down so you fall faster you're accelerating due to gravity g=GM/r².

Very cool and easy to see the logic it explains to me why the apple falls. I've tried to read a bit more about 4 vectors but it's a bit out of my league at this current time.

 

[Buster15]

Thanks. Ive always been a bit confused by gravity I get newtonian gravity GMm/r² and the basics of general relativity, gravitational lensing etc. But why do objects attract? Yes objects with mass bend spacetime and more massive objects bend it more but why does that bend or warped spacetime have the effect of attraction. Why does the apple fall. I can picture a moving object passing by earth having its path bent as it's really taking the shortest path across curved space architecture. Its geodisic path but why an object at rest starts moving.

I read it's to do with an objects 4 vector being affected by gravity. Which says I believe that all objects are moving at the speed of light all the time and c must be conserved. If at rest your 3 spacial velocities are 0 and your path through time is c. But if you're moving let's say very fast your time slows down doesnt it relatively. So your 4 velocity c is conserved. This makes sense to me as time dilation.

Now gravity causes time dilation as well as we know. Gravity slows your time down so to compensate you start moving/falling so c can be conserved and the closer to the centre of the earth you fall the stronger the gravity and the more your time is slowed down so you fall faster you're accelerating due to gravity g=GM/r².

Very cool and easy to see the logic it explains to me why the apple falls. I've tried to read a bit more about 4 vectors but it's a bit out of my league at this current time.

But in the case of the apple falling, is that not to do with its potential or stored energy or inertial mass.

Once released from the tree, it accelerates if a force is applied to it.
And the acceleration is equal to the gravitational force - 9.81m/s divided by its mass.

 

[giggs-beckham]

But in the case of the apple falling, is that not to do with its potential or stored energy or inertial mass.

Once released from the tree, it accelerates if a force is applied to it.
And the acceleration is equal to the gravitational force - 9.81m/s divided by its mass.

But what gives it that potential energy, the mechanism?
All objects will fall at 98.1m/s² if you discount air resistance. And acceleration due to gravity is calculated: g=GM/r²
G is the gravitational constant of the universe which is 6.67×10^-11 nm²/kg².
M is the mass of the earth which incidentally is about 6×10²⁴ kg.
And r is earths radius
I could be misinterpreting what your saying. Apologies if am.

 

[Buster15]

But what gives it that potential energy, the mechanism?
All objects will fall at 98.1m/s² if you discount air resistance. And acceleration due to gravity is calculated: g=GM/r²
G is the gravitational constant of the universe which is 6.67×10^-11 nm²/kg².
M is the mass of the earth which incidentally is about 6×10²⁴ kg.
And r is earths radius
I could be misinterpreting what your saying. Apologies if am.

No my friend. You are not misinterpretating. It is my far less knowledgeable understanding that is the issue. Unfortunately maths is not my strong point. I just try to understand how and why things work. But more in a mechanical as opposed to mathematical way.
So I apologise if I don't fully comprehend all of your points.

I understood that it is the mass of an object that gives the potential energy. It only becomes kinetic energy when it is released.
And then it accelerates as a result of gravitational force F.

The larger the mass, the larger its potential energy. But this is counteracted by the larger the force required to accelerate it.

But. This does nothing to answer the question. What is gravity and how does it work. Which takes us back to your previous post.

 

[giggs-beckham]

No my friend. You are not misinterpretating. It is my far less knowledgeable understanding that is the issue. Unfortunately maths is not my strong point. I just try to understand how and why things work. But more in a mechanical as opposed to mathematical way.
So I apologise if I don't fully comprehend all of your points.

I understood that it is the mass of an object that gives the potential energy. It only becomes kinetic energy when it is released.
And then it accelerates as a result of gravitational force F.

The larger the mass, the larger its potential energy. But this is counteracted by the larger the force required to accelerate it.

But. This does nothing to answer the question. What is gravity and how does it work. Which takes us back to your previous post.

The larger the mass the more gravitational force it has which is calculated as I'm sure you know f=ma mass times acceleration 9.81ms² this is essentially an objects weight. If u catch a ball falling at 9.81 all is well but if u try to catch a car falling at 9.81, all is not well. But the acceleration is the same. Astronauts dropped a feather and hammer on the moon (no air resistance) and both hit the ground simultaneously.
Newtons law of gravitation is something like, gravitational attraction between two objects is proportional to the mass of the two objects and inversely proportional to the distance between their centre of masses squared. This means that the closer you get to earths centre the stronger the gravity is.
Awesomely this means that if you shrank earth down to the size of a small town whilst keeping its mass the same it would be a black hole.

 

[Revan]

Brilliant.

 

[giggs-beckham]

This is how I got into this whole thing because I was confused how a dead star could become a black hole and have such strong gravity, such that light can no longer escape when it has no more mass. Its because it shrinks so small it r is tiny. Reading a tiny amount on newtonian gravity as previously mentioned sorted that one for me and with no maths. I bet you could do the same I love all this and am very grateful of the chat with you.

 

[giggs-beckham]

The problem I've got with string theory is it seems to me to be a mathematical construct designed just to be able to resolve gravity with the other 3 forces.
The first part of the vid is amusingly complicated. The second part basically is most of what I know about this theory which isn't much, all in good time though.

 

[Raoul]

 

[nimic]

I don't think that's quite right. Why would the asteroids fall in towards the inner planets? The asteroids orbit the sun, there's no reason why they wouldn't continue without Jupiter, although they would do it in a slightly less interesting manner.

 

[4bars]

I don't think that's quite right. Why would the asteroids fall in towards the inner planets? The asteroids orbit the sun, there's no reason why they wouldn't continue without Jupiter, although they would do it in a slightly less interesting manner.

Maybe some asteroids would have a smaller orbit and could hit the inner planets? A

 

[nimic]

Maybe some asteroids would have a smaller orbit and could hit the inner planets? A

That would only be the case if Jupiter is somehow speeding them up, which I don't think is happening.

 

[4bars]

That would only be the case if Jupiter is somehow speeding them up, which I don't think is happening.

I mean, without the pull of jupiter maybe some of them they would continue orbiting the sun but closer to the Sun, therfore closer to the orbit of the inner planets?

 

[nimic]

I mean, without the pull of jupiter maybe some of them they would continue orbiting the sun but closer to the Sun, therfore closer to the orbit of the inner planets?

I am not certain, but I don't think that's how it works. Their orbits have been influenced into the shape they are now over a long time by the presence of Jupiter, but they're not really being pulled along by it. Of course if you just removed Jupiter right now it could have some unpredictable long-term consequences, but that's not really the same as saying Jupiter is keeping us safe from the asteroid belt, since Jupiter is sort of to blame for the asteroid belt in the first place.

If you have Universe Sandbox I guess that could be a fun scenario to run.

 

[4bars]

I am not certain, but I don't think that's how it works. Their orbits have been influenced into the shape they are now over a long time by the presence of Jupiter, but they're not really being pulled along by it. Of course if you just removed Jupiter right now it could have some unpredictable long-term consequences, but that's not really the same as saying Jupiter is keeping us safe from the asteroid belt, since Jupiter is sort of to blame for the asteroid belt in the first place.

If you have Universe Sandbox I guess that could be a fun scenario to run.

I mean, I don't know much of anything on astronomy but the normal curiosity or a normal person. I think I read that Jupiter orbit captures random asteriods/ comets or diverts them from entering to the solar system?

 

[nimic]

I mean, I don't know much of anything on astronomy but the normal curiosity or a normal person. I think I read that Jupiter orbit captures random asteriods/ comets or diverts them from entering to the solar system?

I think the general belief these days is that it's a bit of a mixed bag. It stops some stuff, and causes some other stuff. Maybe it was different when the Solar System was younger, as there was a lot more stuff flying around out there.

 

[4bars]

I think the general belief these days is that it's a bit of a mixed bag. It stops some stuff, and causes some other stuff. Maybe it was different when the Solar System was younger, as there was a lot more stuff flying around out there.

Oh I see...

 

[Prometheus]

The problem I've got with string theory is it seems to me to be a mathematical construct designed just to be able to resolve gravity with the other 3 forces.
The first part of the vid is amusingly complicated. The second part basically is most of what I know about this theory which isn't much, all in good time though.

I'd love to learn string theory purely because it's mathematically interesting. I know it's a very controversial idea. The Dream Universe: How Fundamental Physics Lost Its Way by David Lindley was published just last month and it's largely a critique of string theory from what I understand (I haven't read it yet).

 

[giggs-beckham]

I'd love to learn string theory purely because it's mathematically interesting. I know it's a very controversial idea. The Dream Universe: How Fundamental Physics Lost Its Way by David Lindley was published just last month and it's largely a critique of string theory from what I understand (I haven't read it yet).

Hi there. Can you explain what you mean by mathematically interesting.

 

[giggs-beckham]

I think the general belief these days is that it's a bit of a mixed bag. It stops some stuff, and causes some other stuff. Maybe it was different when the Solar System was younger, as there was a lot more stuff flying around out there.

I believe the theory is that if it were not for the presence of Jupiter, earth wouldve been hit too many times for life to have been likely to get going. Schumacher levi 9 a recent example of Jupiter at work.
Also Jupiter's journey through the solar system moving closer to the sun at first then moving out to it's current position. Had the effect of causing the late heavy bombardment which likely gave us our water. So although theory it seems we owe a lot to Jupiter.

 

[Buster15]

The larger the mass the more gravitational force it has which is calculated as I'm sure you know f=ma mass times acceleration 9.81ms² this is essentially an objects weight. If u catch a ball falling at 9.81 all is well but if u try to catch a car falling at 9.81, all is not well. But the acceleration is the same. Astronauts dropped a feather and hammer on the moon (no air resistance) and both hit the ground simultaneously.
Newtons law of gravitation is something like, gravitational attraction between two objects is proportional to the mass of the two objects and inversely proportional to the distance between their centre of masses squared. This means that the closer you get to earths centre the stronger the gravity is.
Awesomely this means that if you shrank earth down to the size of a small town whilst keeping its mass the same it would be a black hole.

Thanks.
Although I don't believe that the Earth, or a relatively small Star could become a Black Hole.

My understanding is that even our Sun will not be big enough or massive enough to collapse sufficiently quick enough to become a Black Hole.

One thing I find fascinating is the process of Nuclear Fusion.
Where the strong force overcomes the Electromagnetic repulsive force to fuse two Hydrogen Protons.
And then how the weak force changes a Proton into a Neutron.
And then how the process results in the formation of Helium 3.
And how a tiny release of mass causes our Sun to burn.

Utterly brilliant in its simplicity.

 

[Prometheus]

Hi there. Can you explain what you mean by mathematically interesting.

String theory is mathematically rigorous. A lot of well established theories in physics don't have rigorous mathematical foundations. For example, the concept of path integral is central to quantum field theory, but it's not mathematically well-defined. Also string theory draws from endless branches of pure mathematics. Naturally, mathematicians are attracted to this and I've heard most people working on string theory are mathematicians by training.

 

[giggs-beckham]

Thanks.
Although I don't believe that the Earth, or a relatively small Star could become a Black Hole.

My understanding is that even our Sun will not be big enough or massive enough to collapse sufficiently quick enough to become a Black Hole.

One thing I find fascinating is the process of Nuclear Fusion.
Where the strong force overcomes the Electromagnetic repulsive force to fuse two Hydrogen Protons.
And then how the weak force changes a Proton into a Neutron.
And then how the process results in the formation of Helium 3.
And how a tiny release of mass causes our Sun to burn.

Utterly brilliant in its simplicity.

No the earth or sun couldn't become a black hole naturally. But if you hypothetically could shrink earth down it would become a black hole. Your phone if shrank small enough would become a black hole very tiny and short lived however.
The sun is fascinating isnt it and ours will go into red giant phase in 5.5 billion years and will swell up in size to consume earth. The night sky will look very different too as Andromeda will be with us.

 

[PedroMendez]

 

[Buster15]

No the earth or sun couldn't become a black hole naturally. But if you hypothetically could shrink earth down it would become a black hole. Your phone if shrank small enough would become a black hole very tiny and short lived however.
The sun is fascinating isnt it and ours will go into red giant phase in 5.5 billion years and will swell up in size to consume earth. The night sky will look very different too as Andromeda will be with us.

Exactly.
The sun is a perfect example of the fantastically fine balance between the laws of physics.

Its temperature is trying to force it to expand, while gravity is trying to make it contract.

As it consumes its Hydrogen store, it will then need to progressively burn its heavier elements.

All the time, loosing mass, resulting in gravity reduction and increased diameter.


It is incredible that it will be able to burn progressively heavier elements right up to Iron, if I have understood that correctly.

Anyway. Another fascinating thing is the way that our universe developed in the first tiny fractions of a second, during the Inflation period.

Minute difference at that phase resulted in a universe capable of producing galaxies, stars, planets and life.

Are you of the view that ours is a single Universe, or do you believe that ours is simply one of possibly an infinite number of different universes continually being born and dying

 

[nimic]

The sun is fascinating isnt it and ours will go into red giant phase in 5.5 billion years and will swell up in size to consume earth. The night sky will look very different too as Andromeda will be with us.

Yep. And complex life on Earth probably has less than a billion years left before it's too hot, maybe "just" a few hundred million. We'll probably want to get off long before then, and to be fair we've got a while to figure it out.

 

[nimic]

It is incredible that it will be able to burn progressively heavier elements right up to Iron, if I have understood that correctly.

I believe the Sun is never going to burn anything but hydrogen and helium. Larger stars go further. I think for it to get right up to (but not including) iron, it has to be something that creates a supernova, hence the very sudden reaction of the star collapsing in on itself due to nuclear fusion essentially losing the battle against gravity (turning into either a neutron star or a black hole).

 

[Buster15]

I believe the Sun is never going to burn anything but hydrogen and helium. Larger stars go further. I think for it to get right up to (but not including) iron, it has to be something that creates a supernova, hence the very sudden reaction of the star collapsing in on itself due to nuclear fusion essentially losing the battle against gravity (turning into either a neutron star or a black hole).

Thank you for the clarification.

 

[2ndTouch]

I am not certain, but I don't think that's how it works. Their orbits have been influenced into the shape they are now over a long time by the presence of Jupiter, but they're not really being pulled along by it. Of course if you just removed Jupiter right now it could have some unpredictable long-term consequences, but that's not really the same as saying Jupiter is keeping us safe from the asteroid belt, since Jupiter is sort of to blame for the asteroid belt in the first place.

If you have Universe Sandbox I guess that could be a fun scenario to run.

Their orbits are influenced by the major gravitational forces in our Solar System, that being the Sun and Jupiter.
When it comes to gravity, distance/proximity matter a lot. That's why Jupiter, while being only a fraction as big as the Sun, still applies enough gravitational pull on these asteroids to prevent them from getting drawn in.

 

[nimic]

Their orbits are influenced by the major gravitational forces in our Solar System, that being the Sun and Jupiter.

That's misleading. The Sun accounts for 99.9% of the mass in the Solar System.

When it comes to gravity, distance/proximity matter a lot. That's why Jupiter, while being only a fraction as big as the Sun, still applies enough gravitational pull on these asteroids to prevent them from getting drawn in.

Why would they be drawn in, though? That's not really how gravity works. And the objects in the asteroid belt have different orbital periods than Jupiter, so half the time they are on the other side of the Sun to Jupiter in any case.

 

[giggs-beckham]

Yep. And complex life on Earth probably has less than a billion years left before it's too hot, maybe "just" a few hundred million. We'll probably want to get off long before then, and to be fair we've got a while to figure it out.

Do you think well destroy ourselves before then?

 

[giggs-beckham]

I believe the Sun is never going to burn anything but hydrogen and helium. Larger stars go further. I think for it to get right up to (but not including) iron, it has to be something that creates a supernova, hence the very sudden reaction of the star collapsing in on itself due to nuclear fusion essentially losing the battle against gravity (turning into either a neutron star or a black hole).

And after the red giant phase itll become a white dwarf star. I find neutron stars fascinating including magnetars.

 

[nimic]

Do you think well destroy ourselves before then?

I'm low-key convinced that humanity is going to end up colonizing the entire galaxy. Just very slowly. Very. Slowly. We just need to avoid blowing ourselves up too badly in the next couple of hundred years. Though I'm sure we'll have another go in a few thousand years anyway.

 

[giggs-beckham]

Exactly.
The sun is a perfect example of the fantastically fine balance between the laws of physics.

Its temperature is trying to force it to expand, while gravity is trying to make it contract.

As it consumes its Hydrogen store, it will then need to progressively burn its heavier elements.

All the time, loosing mass, resulting in gravity reduction and increased diameter.


It is incredible that it will be able to burn progressively heavier elements right up to Iron, if I have understood that correctly.

Anyway. Another fascinating thing is the way that our universe developed in the first tiny fractions of a second, during the Inflation period.

Minute difference at that phase resulted in a universe capable of producing galaxies, stars, planets and life.

Are you of the view that ours is a single Universe, or do you believe that ours is simply one of possibly an infinite number of different universes continually being born and dying

I've never really bought the idea of infinite number of universes. Also the start of the universe in the first second so much happened so quickly they measure in plank time scales. There are more plank times in the first second of the universe than there are seconds in the remaining 13.8 billion years. All cool stuff, are you a multi verse believer.

 

[giggs-beckham]

I'm low-key convinced that humanity is going to end up colonizing the entire galaxy. Just very slowly. Very. Slowly. We just need to avoid blowing ourselves up too badly in the next couple of hundred years. Though I'm sure we'll have another go in a few thousand years anyway.

I wish I had your faith I wish we could find other life in the universe and be able to traverse the galaxy like star trek. I just think it is beyond possibility. You look at what were like as a species and were so far off not just technologically. But one day who knows you could be right.

 

[giggs-beckham]

String theory is mathematically rigorous. A lot of well established theories in physics don't have rigorous mathematical foundations. For example, the concept of path integral is central to quantum field theory, but it's not mathematically well-defined. Also string theory draws from endless branches of pure mathematics. Naturally, mathematicians are attracted to this and I've heard most people working on string theory are mathematicians by training.

As far as I'm aware its unprovable as a string would be too small to detect. I saw a documentary years ago that said if an atom were the size of the solar system a string would be the size of a tree on earth.
Do you study or are really good at maths? I've never really been into it until recently as previously mentioned in a previous post. I must say it's very fun and rewarding to learn. I haven't looked at string theory maths as its probably well out side of what I can do currently. This is the reason I'm trying to learn maths to fill in the gaps as it were.

 

[Buster15]

I've never really bought the idea of infinite number of universes. Also the start of the universe in the first second so much happened so quickly they measure in plank time scales. There are more plank times in the first second of the universe than there are seconds in the remaining 13.8 billion years. All cool stuff, are you a multi verse believer.

Increasingly so yes.
The reason behind this is that during those minute fractions of a second of the birth of our universe, so many variables just happened to result in the universe we inhabitant.

A tiny fraction more matter than antimatter.

And just the right amount of matter to drive its expansion.

And just enough ripples in the early universe to allow gravity to start to pull that matter into the birthplaces where galaxies could form.

The list of such variables is such that the probability of all these occurrences turning out just right is extremely remote.

I have read and tried to understand the cosmic inflation theory and this is now becoming almost mainstream acceptance.
It proposes a region where baby universes are forming.
Some don't develop and give back their energy. But some do develop, each with differing characteristics. And our universe is one of possibly an infinite number of different universes. And all we know about is the observable part. Who knows what exists outside that observable part.

 

[giggs-beckham]

Increasingly so yes.
The reason behind this is that during those minute fractions of a second of the birth of our universe, so many variables just happened to result in the universe we inhabitant.

A tiny fraction more matter than antimatter.

And just the right amount of matter to drive its expansion.

And just enough ripples in the early universe to allow gravity to start to pull that matter into the birthplaces where galaxies could form.

The list of such variables is such that the probability of all these occurrences turning out just right is extremely remote.

I have read and tried to understand the cosmic inflation theory and this is now becoming almost mainstream acceptance.
It proposes a region where baby universes are forming.
Some don't develop and give back their energy. But some do develop, each with differing characteristics. And our universe is one of possibly an infinite number of different universes. And all we know about is the observable part. Who knows what exists outside that observable part.

Cool I haven't heard of inflation with regards to multiverse theory, I'd be interested to read more so will.
As far as I know the singularity that the universe came from had quantum fluctuations or irregularities so as it expanded or inflated those irregularities remained. This can be detected in the cosmic microwave background which is the earliest light we can see some 380,000years after the big bang.
Areas of this signature are more and less dense and as I believe these denser areas coalesced to form the stars and galaxies.
I'm fascinated by the un observable universe, how far do the stars and galaxies go and if they're infinite then how can the universe be finite in age (13.8 billion years)