The Outer Space Thread

[skinsfan4128]

21 hours ago, CousinsCowgirl84 said:

And eventually it will all be ripped into nothingness.

Here she comes to wreck the day. 🤣

 

I have to admit though, the images we're seeing is very humbling, in my opinion.  Just thinking of small we really are compared to the overall scope of the universe vs. how blessed we are to be alive here on this rock we call Earth 🌎. 

 

Very humbling indeed.

 

HTTR!

[mistertim]

1 hour ago, skinsfan4128 said:

Here she comes to wreck the day. 🤣

 

I have to admit though, the images we're seeing is very humbling, in my opinion.  Just thinking of small we really are compared to the overall scope of the universe vs. how blessed we are to be alive here on this rock we call Earth 🌎. 

 

Very humbling indeed.

 

HTTR!

 

We're also absolutely enormous...just depends on your reference frame.

 

If you scaled a Planck length up to the size of a human, the human would be about 100 million times the size of the observable universe.

[PokerPacker]

Site gives comparisons between Hubble and Webb. https://johnedchristensen.github.io/WebbCompare/

Edited July 13, 2022 by PokerPacker

[Jabbyrwock]

9 hours ago, mistertim said:

 

My math game isn't even close to strong enough to figure this out myself. Is it true that the equations in Relativity say that it's actually time dilation that causes gravity and not vice-versa, since in most of the universe the vast majority of what mass "curves" is time and not space?

 

Sorry Tim, GR's not my field.  Haven't re-upped my GR game since grad school.  From hazy recollection 20 odd years ago, I think this kind of argument only applies in a weak field, low speed approximation...but don't quote me on that.

[CousinsCowgirl84]

39 minutes ago, mistertim said:

 

We're also absolutely enormous...just depends on your reference frame.

 

If you scaled a Planck length up to the size of a human, the human would be about 100 million times the size of the observable universe.

Ok space bro I don’t understand what that means but stop calling me large.

[mistertim]

48 minutes ago, CousinsCowgirl84 said:

Ok space bro I don’t understand what that means but stop calling me large.

 

[Corcaigh]

1 hour ago, mistertim said:

 

We're also absolutely enormous...just depends on your reference frame.

Here’s a helpful illustration of the scale of massive objects in the Universe. Watch until the end.

 

 

[Corcaigh]

10 hours ago, mistertim said:

So gravity isn't actually a force or a result of curvature of space, but the result of time being different at different points of any object, especially one near a massive object?

It is spacetime that is curved rather than just space. But as we don’t understand what mass is and spacetime is just an idea, this cartoon sums it up.

 

 

 But as we’re talking about rubber sheets and spacetime being curved by massive objects …

 

 

[CousinsCowgirl84]

Nvm

 

 

 

Edited July 13, 2022 by CousinsCowgirl84

[mistertim]

16 minutes ago, Corcaigh said:

It is spacetime that is curved rather than just space. But as we don’t understand what mass is and spacetime is just an idea, this cartoon sums it up.

 

 

 

Right, but IIRC (and I'm really just going on memory here) the presence of mass doesn't warp space and time equally, at least in "most" scenarios outside of extreme objects like black holes and neutron stars. The majority of what is warped in "normal" gravitational scenarios is time.

 

Ah, found the video I was looking for.

 

 

 

4 minutes ago, CousinsCowgirl84 said:

Gravitational lensing bends light (photons) not spacetime. Gravity bends spacetime. Eg, the closer you are to a black hole the slower time progresses for you from the perspective of a person further away from the black hole.

 

Right, but (as the video above talks about) it seems that it might actually be time dilation that causes gravity, not the other way around.

Edited July 13, 2022 by mistertim

[CousinsCowgirl84]

3 minutes ago, mistertim said:

 

Right, but IIRC (and I'm really just going on memory here) the presence of mass doesn't warp space and time equally, at least in "most" scenarios outside of extreme objects like black holes and neutron stars. The majority of what is warped in "normal" gravitational scenarios is time.

 

Ah, found the video I was looking for.

 

 

 

 

Right, but (as the video above talks about) it seems that it might actually be time dilation that causes gravity, not the other way around.

I have not heard this before. I’ll read about it soon 👍 

[Corcaigh]

I don’t understand his argument. Objects accelerate toward one another due to the curvature of spacetime.

 

Edited July 13, 2022 by Corcaigh
Typo

[DCSaints_fan]

11 hours ago, mistertim said:

 

My math game isn't even close to strong enough to figure this out myself. Is it true that the equations in Relativity say that it's actually time dilation that causes gravity and not vice-versa, since in most of the universe the vast majority of what mass "curves" is time and not space?

 

So gravity isn't actually a force or a result of curvature of space, but the result of time being different at different points of any object, especially one near a massive object?

Do you mean the equations in special relativity or general relativity?  Or both I guess?  I had never heard the "time dilation causes gravity" theory.

 

Gravity is still one of the big areas of research in physics.  There is the GR model by Einstein, in which gravity causes local distortion of space time, such that not even light which is massless remains unaffected.  The GR model has been shown to be consistent with observations - one of the most famous being the aberrations in the observed orbit of Mercury.   There was also the discovery of gravity waves by LIGO in 2015 (predicted by Einstein) But (to my knowledge), no one has been able to reconcile it with quantum mechanics (i.e., quantum gravity), which acts on a small scale and where the gravitational force is incredibly weak.  Then there is the whole dark matter / dark energy problem, where gravity by itself fails to account the observations of an expanding universe, and is the only one of the four(or three) fundamental forces which could act at such a scale. 

 

[CousinsCowgirl84]

27 minutes ago, mistertim said:

 

Right, but IIRC (and I'm really just going on memory here) the presence of mass doesn't warp space and time equally, at least in "most" scenarios outside of extreme objects like black holes and neutron stars. The majority of what is warped in "normal" gravitational scenarios is time.

 

Ah, found the video I was looking for.

 

 

 

 

Right, but (as the video above talks about) it seems that it might actually be time dilation that causes gravity, not the other way around.

on one hand the video is from PBS, on the other hand the internet is very meh about the whole idea. There isn’t even a Wikipedia page for it.

 

 

[Jabbyrwock]

4 minutes ago, Corcaigh said:

I don’t understand his argument. Objects accelerate toward one another die to the curvature of spacetime.

Yea, I'm with you on this @Corcaigh.  There seems to be some confusion here between space time curvature and gravitational attraction.  I mean, if I'm in a reference frame with constant acceleration, from my perspective I feel a constant gravitational attraction and by GR I certainly see clocks running faster the farther they are from me.  But an observer in a rest frame would not see a similar time dilation effect.  Space time curvature should be agreed upon between the rest and accelerating frames.  But if time dilation caused curvature that wouldn't be the case here.  Honestly not sure where PBS spacetime got this.

[mistertim]

9 hours ago, Jabbyrwock said:

Yea, I'm with you on this @Corcaigh.  There seems to be some confusion here between space time curvature and gravitational attraction.  I mean, if I'm in a reference frame with constant acceleration, from my perspective I feel a constant gravitational attraction and by GR I certainly see clocks running faster the farther they are from me.  But an observer in a rest frame would not see a similar time dilation effect.  Space time curvature should be agreed upon between the rest and accelerating frames.  But if time dilation caused curvature that wouldn't be the case here.  Honestly not sure where PBS spacetime got this.

 

I don't think they're saying that time dilation causes curvature, but that it causes gravity. The curvature is caused by mass/energy being present, and in most "normal" cases outside of extreme areas like black holes and near neutron stars the majority of what is actually "curved" is in the time dimension, not the space dimensions.

 

The difference in time between two parts of the same object causes its four-velocity to "angle" towards where the clocks run slower, which is also towards the mass/energy that's causing the spacetime curvature. 

 

Not sure exactly where they got it either, though there are other videos about it as well. They don't really show a ton of math on PBS Spacetime, but O'Dowd is an astrophysicist so I doubt he'd put something out there that had no mathematical or theoretical basis.

Edited July 13, 2022 by mistertim

[Corcaigh]

5 hours ago, mistertim said:

 

I don't think they're saying that time dilation causes curvature, but that it causes gravity.

I’d still start from the position that gravity is a force we experience due to the curvature of spacetime.

 

But, I will bow out of the discussion as I am certainly not a professional or even well read on gravity. My Electrical Engineering versus pure Physics background frankly causes me much frustration with the lack on of clarity or consensus on whether gravity ‘force’ and gravitons exist and can fit into the Standard Model, WTF dark matter and dark energy actually are (and why didn’t we know about them for so long), and that the Standard Model/QM and GR are as incompatible as they were a hundred years ago.

 

Theoretical physicists need to bring testable theories or GTFO.

 

 

[NickyJ]

On 7/12/2022 at 2:46 PM, PleaseBlitz said:

I don't know what any of this is or means, but it sure is pretty.

 

I've been playing Mass Effect Andromeda lately, and I hate to tell you, but that's The Scourge. It's a bad thing and it's going to eat all our spaceships.

[DCSaints_fan]

On 7/13/2022 at 8:20 AM, mistertim said:

 

I don't think they're saying that time dilation causes curvature, but that it causes gravity. The curvature is caused by mass/energy being present, and in most "normal" cases outside of extreme areas like black holes and near neutron stars the majority of what is actually "curved" is in the time dimension, not the space dimensions.

 

The difference in time between two parts of the same object causes its four-velocity to "angle" towards where the clocks run slower, which is also towards the mass/energy that's causing the spacetime curvature. 

 

Not sure exactly where they got it either, though there are other videos about it as well. They don't really show a ton of math on PBS Spacetime, but O'Dowd is an astrophysicist so I doubt he'd put something out there that had no mathematical or theoretical basis.

Time-dilation is a consequence of the axioms of special relativity.  So is length-contraction.  We can observe time dilation effect (and length-contraction), but not observe the effects of GR, gravity or space-time curvature (to any degree we can measure)  All you need to do to observe the time-dilation effect is to accelerate a particle to close to the speed of light and/or have it travel at a high enough speed for a long enough time.  This particle can have very little rest-mass-energy (in-fact we can only accelerate particles with low RME to anywhere close to the speed of light), so it would not cause a disruption the way a very heavy object like the Sun would. So I'm not sure how time dilation could cause curvature.  

I would also thrown in a disclaimer that I am not a physicist.

Edited July 14, 2022 by DCSaints_fan

[Simmsy]

3 hours ago, NickyJ said:

I've been playing Mass Effect Andromeda lately, and I hate to tell you, but that's The Scourge. It's a bad thing and it's going to eat all our spaceships.

I scienced it, he's right. Make him president of the galaxy!

[mistertim]

1 hour ago, DCSaints_fan said:

Time-dilation is a consequence of the axioms of special relativity.  So is length-contraction.  We can observe time dilation effect (and length-contraction), but not observe the effects of GR, gravity or space-time curvature (to any degree we can measure)  All you need to do to observe the time-dilation effect is to accelerate a particle to close to the speed of light and/or have it travel at a high enough speed for a long enough time.  This particle can have very little rest-mass-energy (in-fact we can only accelerate particles with low RME to anywhere close to the speed of light), so it would not cause a disruption the way a very heavy object like the Sun would. So I'm not sure how time dilation could cause curvature.  

I would also thrown in a disclaimer that I am not a physicist.

 

I literally said in the post you quoted that they're not saying time dilation causes curvature. They're saying it causes gravity. Mass/energy causes the curvature, and in "normal" situation (ie not in a black hole or near a neutron star) it's actually time that "curves" much more than space.

 

So it's basically taking the notion that the curvature of spacetime causes gravity and it's gravity that causes time dilation on its head, and saying that it's time dilation that causes gravity, not the curvature of space.

[Jabbyrwock]

3 hours ago, mistertim said:

 

I literally said in the post you quoted that they're not saying time dilation causes curvature. They're saying it causes gravity. Mass/energy causes the curvature, and in "normal" situation (ie not in a black hole or near a neutron star) it's actually time that "curves" much more than space.

 

So it's basically taking the notion that the curvature of spacetime causes gravity and it's gravity that causes time dilation on its head, and saying that it's time dilation that causes gravity, not the curvature of space.

 

Damnit Tim, you're gonna drive me to go dig my GR book out of the box in the garage and do work this weekend, aren't ya?  And here I just got over Covid and had a solid weekend of drinkin' planned.

 

Actually...just kidding.  I already pulled a book out.  Carlo Rovelli, who I actually know from my graduate days and is a well respected person in GR, says in his book (page 80, General Relativity the Essentials):

 

"Masses subjected to the gravitational force follow geodesics in a spacetime whose only difference from Minkowski space is a local modification of g00, that is, a modification of the local speed at which time passes (compared to the speed at which it passes elsewhere). Therefore, in general relativity we can say that things fall towards a mass because a mass slows down time in its vicinity"

 

...never heard this interpretation before, and I'm going through the math just now to dig into it a bit more and understand limiting conditions.  I'm still having problems with the interpretation from a cause and effect stand point...I'd rather say its a consistent description given a coordinate transformation.  Still tho, definitely interesting thoughts.  Thanks @mistertim .

 

[DCSaints_fan]

3 hours ago, mistertim said:

 

I literally said in the post you quoted that they're not saying time dilation causes curvature. They're saying it causes gravity. Mass/energy causes the curvature, and in "normal" situation (ie not in a black hole or near a neutron star) it's actually time that "curves" much more than space.

Can you really decouple the concepts of spacetime curvature and gravity?  Because I thought that was one of the major points of GR

  

3 hours ago, mistertim said:

So it's basically taking the notion that the curvature of spacetime causes gravity and it's gravity that causes time dilation on its head, and saying that it's time dilation that causes gravity, not the curvature of space.

To me this is like saying smoke causes fire, because when see smoke you (almost always) see fire.

 

Also I would like to reiterate, you can (or should, I suppose, as its a tough experiment) be able to see time dilation without gravity.  Time dilation is a consequence of SR, which doesn't even consider gravity.   Small objects like atomic clocks exhibit it, for instance, and it doesn't have anything to do with the gravitational field they are in.  Granted, we are performing most of our experiments on Earth or near earth orbit, so kind of hard to get everything out of a gravitational field ... but the point is the gravitational field, is not the reason why we see time dilation .. its the relative motion of the two objects ... you should get the same whether you perform the experiment on Earth or in deep space far away from gravitational influence.

 

As it turns out, it does appear that theory predicts that particles moving at relativistic speeds do indeed cause a gravitational field apart from what you would expect given their rest mass energy (except maybe not photons?) ... at least in theory, I'm not sure if anyone's performed this particular experiment ... though it should be very difficult, because hard to accelerate large particles to speeds at which you start to see relativistic effects that don't have to do with time dilation (e.g, length contraction), you have to be pretty close often > 0.9c, which takes quite a bit of energy, and the effects of gravity on nearby particles at rest, will last like picoseconds. 

Edited July 14, 2022 by DCSaints_fan

[CousinsCowgirl84]

3 hours ago, mistertim said:

 

I literally said in the post you quoted that they're not saying time dilation causes curvature. They're saying it causes gravity. Mass/energy causes the curvature, and in "normal" situation (ie not in a black hole or near a neutron star) it's actually time that "curves" much more than space.

 

So it's basically taking the notion that the curvature of spacetime causes gravity and it's gravity that causes time dilation on its head, and saying that it's time dilation that causes gravity, not the curvature of space.

What is time? The way I understand it is that time and space cannot be separated. If time causes gravity then moving fast would increase gravity since acceleration is equivalent to gravity.

[mistertim]

21 minutes ago, DCSaints_fan said:

Can you really decouple the concepts of spacetime curvature and gravity?  Because I thought that was one of the major points of GR

  

 

It's not decoupling the concepts of spacetime curvature and gravity. It's changing the order of operations and the causal relationship. Instead of the curvature of spacetime causing gravity which then causes time dilation, the curvature of spacetime causes time dilation which causes gravity.

 

20 minutes ago, CousinsCowgirl84 said:

What is time? The way I understand it is that time and space cannot be separated. If time causes gravity then moving fast would increase gravity since acceleration is equivalent to gravity.

 

Time and space can't be separated. And they're not saying time causes gravity, they're saying the difference in time between two reference frames causes it. 

 

35 minutes ago, Jabbyrwock said:

 

Damnit Tim, you're gonna drive me to go dig my GR book out of the box in the garage and do work this weekend, aren't ya?  And here I just got over Covid and had a solid weekend of drinkin' planned.

 

 

 

See now I feel bad. Disregard everything I've been saying, nothing to see here, folks!

 

Edited July 14, 2022 by mistertim