GRS1915+105 and SR

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1 Nicolaas Vroom GRS1915+105 and SR maandag 10 december 2001 13:31
2 Steve Willner Re: GRS1915+105 and SR woensdag 12 december 2001 12:45
3 Ted Rosencrantz Re: GRS1915+105 and SR donderdag 13 december 2001 0:32
4 Nicolaas Vroom Re: GRS1915+105 and SR zaterdag 15 december 2001 18:15
5 Nicolaas Vroom Re: GRS1915+105 and SR zaterdag 15 december 2001 18:15


1 GRS1915+105 and SR

Van: Nicolaas Vroom
Onderwerp: GRS1915+105 and SR
Datum: maandag 10 december 2001 13:31

At page 501 of Nature no 6863 29 Nov 2001 "A new spin on black-hole masses" we read: "The apparent speed is a well-known optical illusion caused by special relativity, but the true velocity of the jet material is calculated to be greater than 90% of the speed of light"

IMO an optical illusion and SR have nothing in common. The apparent speed is either an optical illusion or it can be explained by SR but it can not be both

A different line of reasoning is that SR (part of) is an optical illusion but I doubt that.

When you will go to my home page http://users.pandora.be/nicvroom and you select train experiment part 1 or program 4 I argue that when you move a rod away from you its length appears shortened and when you move a rod towards you its length appears longer however both effects are optical illusions. The same for effects are for speed ie it is an optical illusion and has nothing to do with SR

Or something of my understanding is wrong.

One very interesting piece of information are the MEASURED delta z values from:
1 GRS1915+105 the source microquasar.
2. The approaching component
3. The receding component

The original article in Nature 6492 at page 48 I read:
"The spectral lines arising in the approaching and receding components should have mean redshifts of 0.75 and 2.36 respectivily (as a result of relativistic effects both should appear redshifted)"

I interpret this as, that as of 1994, the redshift values were not measured.

In relation to the Big Bang if you study the distance as for example quasars at z=3 you should be carefull not to measure the dz of the receding components of the quasar but the dz of the real quasar

Nicolaas Vroom

[Mod. note: in quasars, as opposed to Galactic microquasars, the jets are synchrotron emission and so do not contain spectral lines. You're right, however, that the optical illusion that gives rise to apparent superluminal motion has nothing much to do with SR. See http://sciastro.astronomy.net/sci.astro.8.FAQ


2 GRS1915+105 and SR

Van: Steve Willner
Onderwerp: Re: GRS1915+105 and SR
Datum: woensdag 12 december 2001 12:45

In article , Nicolaas Vroom writes:
> At page 501 of Nature no 6863 29 Nov 2001 "A new spin on black-hole masses" we read:
"The apparent speed is a well-known optical illusion caused by special relativity, but the true velocity of the jet material is calculated to be greater than 90% of the speed of light"

IMO an optical illusion and SR have nothing in common.

Perhaps one can object to the phrase "optical illusion," but the physics of the situation are well known.

If you multiply the apparent angular speed by the distance to the object, you come up with a speed faster than the speed of light. The point is that this does not imply that any physical object is travelling faster than light; special relativity (and an assumption about or knowledge of the inclination angle) enables you to calculate the true speed of the jet material.

-- Steve Willner Phone 617-495-7123 swillner@cfa.harvard.edu Cambridge, MA 02138 USA
(Please email your reply if you want to be sure I see it; include a valid Reply-To address to receive an acknowledgement. Commercial email may be sent to your ISP.)


3 GRS1915+105 and SR

Van:
Onderwerp: Re: GRS1915+105 and SR
Datum: donderdag 13 december 2001 0:32

In article , Steve Willner wrote:

> If you multiply the apparent angular speed by the distance to the object, you come up with a speed faster than the speed of light. The point is that this does not imply that any physical object is travelling faster than light; special relativity (and an assumption about or knowledge of the inclination angle) enables you to calculate the true speed of the jet material.

It's perhaps worth pointing out that you don't even need special relativity to understand the phenomenon. It happens even in classical kinematics.

Say an object is moving with a velocity component of 3/6 times the speed of light in the direction transverse to your line of sight, and a component of 4/6 times the speed of light towards you. Then its true velocity is 5/6 times the speed of light. (I know I could reduce the fractions in the two components, but I wanted the 3-4-5 triangle to be explicit.)

Now, suppose this object emits two pulses of light one year apart. During that one year, the object has moved 3/6 light-year transverse to your line of sight, so you'll see an apparent displacement of half a light-year. The two pulses of light will arrive at your location only a third of a light-year apart, though. (They were emitted one year apart, but the second one had 2/3 of a light-year less distance to travel in order to reach you, since the object had moved towards you by this amount during that year.)

So you see an apparent displacement of 1/2 light-year in an apparent time of 1/3 year. If you're sufficiently naive, you conclude that the object has a transverse velocity of 1.5 times the speed of light.

So you don't need special relativity to understand where this "optical illusion" comes from. Of course, you do need special relativity to understand why it's interesting: without special relativity, there wouldn't be any problem with something (apparently) moving faster than the speed of light.

-Ted


4 GRS1915+105 and SR

Van:
Onderwerp: Re: GRS1915+105 and SR
Datum: zaterdag 15 december 2001 18:15

Steve Willner schreef in berichtnieuws mt2.0-2136-1008157532@star.bris.ac.uk...
> In article , Nicolaas Vroom writes:
> > At page 501 of Nature no 6863 29 Nov 2001 "A new spin on black-hole masses" we read: "The apparent speed is a well-known optical illusion caused by special relativity, but the true velocity of the jet material is calculated to be greater than 90% of the speed of light"

IMO an optical illusion and SR have nothing in common.

>

Perhaps one can object to the phrase "optical illusion," but the physics of the situation are well known.

If you multiply the apparent angular speed by the distance to the object, you come up with a speed faster than the speed of light. The point is that this does not imply that any physical object is travelling faster than light; special relativity (and an assumption about or knowledge of the inclination angle) enables you to calculate the true speed of the jet material.

If I understand above you need Lorentz transformations in order to explain and to calculate the true speed. Implying that the wording "optical illusion" does not apply

My understanding (and so the moderator See http://sciastro.astronomy.net/sci.astro. is that any new physics (SR) is not required.

My understanding comes from studying a rod. (See http://users.pandora.be/nicvroom/ When this rod moves away both its apparent length and its apparent speed decrease. When this rod moves towards the observer its apparent length and speed both increase. You can argue that the length in both cases also diminishes as a result of length contraction ie SR. If that is the case I will expand my comments.

Program 4 was written around 1993.

Nicolaas Vroom


5 GRS1915+105 and SR

Van:
Onderwerp: Re: GRS1915+105 and SR
Datum: zaterdag 15 december 2001 18:15

schreef in berichtnieuws mt2.0-928-1008199944@star.bris.ac.uk...
> Now, suppose this object emits two pulses of light one year apart. During that one year, the object has moved 3/6 light-year transverse to your line of sight, so you'll see an apparent displacement of half a light-year. The two pulses of light will arrive at your location only a third of a light-year apart, though. (They were emitted one year apart, but the second one had 2/3 of a light-year less distance to travel in order to reach you, since the object had moved towards you by this amount during that year.)

So you see an apparent displacement of 1/2 light-year in an apparent time of 1/3 year. If you're sufficiently naive, you conclude that the object has a transverse velocity of 1.5 times the speed of light.

So you don't need special relativity to understand where this "optical illusion" comes from. Of course, you do need special relativity to understand why it's interesting: without special relativity, there wouldn't be any problem with something (apparently) moving faster than the speed of light.

Assuming that the "you" above is the Observer than it is important if you assume that all values are measured in the same reference frame (rest frame) of the Observer.
For example:
"suppose this object emits two pulses of light one year apart" means that you need (at least) two clocks in the rest frame 5/6 light year apart (2/3 light year apart in line of sight) The "one year" means than the difference in time when the object moves from the first to the second clock.

A different way to do this "experiment" is performing measurements in the rest frame of the object. For example: emitting "two pulses one year apart" with one clock which moves with the object.

If you compare this clock in the rest frame of the object with the clocks in the rest frame of the observer than the first one will run slower compared with the second ones. To understand that (and only that) you need SR.

IMO the apparent length of the object also changes.
When you consider the object as a rod with length l (in the rest frame of the observer) than any moment the observer sees both the beginning and end. (The rod moves almost in the direction of line of sight)
When the rod moves towards you, you will not see the beginning and end where those points are at the same moment. You will see the end at an earlier moment (when the rod was further away) resulting that apparent length that you see is longer.

When the rod moves away from you, the reverse is true and the apparent length that you see is shorter.

Including SR complicates this picture. (Assuming my understanding is correct) When the rod moves away from you what you see will be even more shorter. When the rod moves towards you what you see will be less longer.

Nicolaas


Created: 23 December 2001

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