B Revealing Secrets of Distant Supernova DES16C2nm: 10.5 Billion Years Ago

[Viopia]

That's a coordinate speed - as I said, it can be anything you like. In this case

If an astonaut is in orbit very close to a supermassive black hole, so he is not spaghettified, his time will be runnng very slowly form the Earth's frame of reference. When you use the word ''coordinate'' do you mean that the astronaut's frame of reference is one coordinate and the Earth's frame of reference is another coordinate. If so, the astronaut's time will be running normaly to the astronaut, but (depending on how close he is to the black hole) the outside universe will be speeded up and could easilly surpass the speed of light from the astronought's frame of reference if he is close enough to the black hole. If this is what coordinates mean, then it would certainly be possible for objects to exceed the speed of light (as they vanish from view) from an observer's frame of reference if you choose the right coordinate.

 

[Viopia]

And all your posts show that what is logical for you is not necessarily logical for physicists and physics. If you wan't to learn physics you have to conform to physics, not the other way around.

Don't you try to get your physics students to understand what the mathematics is telling them? To understand, your students will have to use their own logic, not your logic. When a subject cannot be logically understood, like in quantum physics, students have been told to ''shut up and calculate''. This only means that the mathematical process is undertood.

 

[weirdoguy]

To understand, your students will have to use their own logic, not your logic.

No, they will have to adjust their logic, if it doesn't match with physics. Universe does not care about your faulty logic. Every physics student, including myself, had to go through this process, so I don't know why you think it wouldn't apply to you.

 

[Viopia]

No, they will have to adjust their logic, if it doesn't match with physics. Universe does not care about your faulty logic. Every physics student, including myself, had to go through this process, so I don't know why you think it wouldn't apply to you.

Of course it applies to me. I havn't been able to adjust my logic yet but I may be abe to do so if I learn more. Have you adjusted your logic to understand quantum physics yet?

 

[weirdoguy]

Have you adjusted your logic to understand quantum physics yet?

Long time ago. I had to, otherwise I wouldn't be able to finish my masters in physics.

 

[Orodruin]

Don't you try to get your physics students to understand what the mathematics is telling them? To understand, your students will have to use their own logic, not your logic. When a subject cannot be logically understood, like in quantum physics, students have been told to ''shut up and calculate''. This only means that the mathematical process is undertood.

You are using the word ”logic” in the wrong way. The theory of GR is logically consistent (although it does raise some questions) and all of the computations follow logic. What you are confusing it with is whether or not it appears to fit into your own mental framework, which the theory has no obligation to do. If that is your use of ”logic” then no, students should not use their own ”logic” because it will mostly be wrong. The point of teaching GR is to provide the students with the appropriate ”logic” and teach them what the theory actually states.

 

[Viopia]

can be more or less anything you want since it depends on how you choose to define your coordinates

I am still interested in any response to my question (*51) regarding the use of the word ''coordinate''.

 

[Orodruin]

When you use the word ''coordinate'' do you mean that the astronaut's frame of reference is one coordinate and the Earth's frame of reference is another coordinate.

Frames of reference are not as unambiguous in GR as they are in SR. Coordinates are (local or global) assignments of four numbers to events in spacetime, typically (but not necessarily) three spatial and one time coordinate. Since the assignment is arbitrary, the coordinate speeds (coordinate distance per coordinate time) are arbitrary.

 

[Ibix]

Just to add to Orodruin's response, it's trivially easy to make coordinate speeds faster than light. No black holes needed. Just turn around 360°. In a coordinate frame attached to you the Sun just circled around you (a distance of about 50 light minutes) in a second or so.

But at no point did any massive object overtake a light pulse. That's the distinction between coordinate speeds (which can be anything) and physically meaningful speeds.

 

[Viopia]

For a photon, while locally it always moves at c, it can have any approach velocity whatsoever - including 0 and negative, i.e. being 'stopped' or carried away by expansion despite being sent towards us.

Just to add to Orodruin's response, it's trivially easy to make coordinate speeds faster than light. No black holes needed. Just turn around 360°. In a coordinate frame attached to you the Sun just circled around you (a distance of about 50 light minutes) in a second or so.

But at no point did any massive object overtake a light pulse. That's the distinction between coordinate speeds (which can be anything) and physically meaningful speeds.

It is no wonder I needed time to digest what Bandersnatch said. I thought we were talking about real velocities. Ibix's comment about the Sun can be described in the following way:- As a you ''turn around'' the Sun does not circle you, you merely turn around so that the light hitting your retina (after passing the crystalline lens in your eye) scribes an ark on your retina. The light hitting your retina only tavells around an inch per second which is far less than the speed of light.

 

[Orodruin]

It is no wonder I needed time to digest what Bandersnatch said. I thought we were talking about real velocities. Ibix's comment about the Sun can be described in the following way:- As a you ''turn around'' the Sun does not circle you, you merely turn around so that the light hitting your retina (after passing the crystalline lens in your eye) scribes an ark on your retina. The light hitting your retina only tavells around an inch per second which is far less than the speed of light.

This is not the point he was making.

The point is that the coordinate speeds of a stationary object in a rotating coordinate system are directly proportional to the distance and if the distance is far enough then the coordinate speeds easily exceed the speed of light.

How fast the spot of light moves on the retina is also not bounded by the speed of light. The light at subsequent moments is not the same light pulse. There is no light moving along the retina.

 

[Ibix]

As a you ''turn around'' the Sun does not circle you,

Sure it does. That motion is no more or less real than any other.

 

[Viopia]

Sure it does. That motion is no more or less real than any other.

If what you say is correct, the Earth traveling around the Sun could be thought of as the Sun rotating while the Earth is stationary. If the the Earth had no orbital velocity it would crash into the Sun. This means there is a difference.

 

[Viopia]

There is no light moving along the retina.

No there isn't any light moving on the retina, just lke the Sun is not moving faster than the speed of light.

 

[weirdoguy]

the Earth traveling around the Sun could be thought of as the Sun rotating while the Earth is stationary.

Well, yes. What's the problem with that? Motion is relative. That is the very basic thing.

 

[Ibix]

Actually, working in a rotating frame where the Earth is stationary is one of the easiest ways to work out orbital dynamics. You get a centrifugal potential that makes it different from the non-rotating case, but it is not any more or less real.

 

[Ibix]

No there isn't any light moving on the retina, just lke the Sun is not moving faster than the speed of light.

Why do you ask questions and then, when we answer or explain, just say "no"?

 

[Orodruin]

No there isn't any light moving on the retina, just lke the Sun is not moving faster than the speed of light.

That’s the point. However, it is not ”just like”. In the former case it is a question of taking a speed of something that is not an actual object and in the latter a coordinate speed that is the coordinate speed of the Sun - an actual object.

Also, please be more careful with your quotes. You just attributed one of your answers to me making it seem I said something I did not.

 

[Viopia]

That’s the point.

Also, please be more careful with your quotes. You just attributed your answer to me making it seem I said something I did not.

I am sorry the quote was not from you. I don't know how this couild have happened. I was trying to answer two questions close together and used the prompt after highlighting the part I wanted to answer.

 

[Viopia]

Why do you ask questions and then, when we answer or explain, just say "no"?

I sometimes don't understand the answers. When this happens I try to say what does not make sense to me.