Is it possible to determine if space is fixed or moving?

  • Context: Graduate 
  • Thread starter Thread starter Emu
  • Start date Start date
  • Tags Tags
    Space
Click For Summary

Discussion Overview

The discussion revolves around the nature of space and whether it can be determined if space is fixed or in motion. Participants explore various aspects of space, including its properties, the implications of motion, and the relationship between space and objects within it. The conversation touches on theoretical considerations rather than empirical observations, avoiding relativistic frameworks and focusing on conceptual understandings of space.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants propose that space has properties such as volume, permeability, and permittivity, and question whether these properties allow for the determination of space's motion.
  • Others argue that the question of space moving must be contextualized relative to other objects, as all observed motion is relative.
  • It is suggested that there is no measurable property of space that indicates motion, as Special Relativity has removed such distinctions.
  • Some participants assert that space is expanding, while others challenge the notion of space having a velocity, suggesting that this leads to confusion about the nature of motion.
  • One viewpoint emphasizes that if space is defined as "nothing," it complicates the concept of motion, as motion implies a medium that can be occupied.
  • Participants discuss Einstein's views on space and motion, with some interpreting his statements as indicating that motion cannot be applied to space itself.
  • There is a debate about whether Einstein's ideas about space would change if he had known about cosmological expansion, with some suggesting that his views might have been more nuanced.
  • Concerns are raised about the implications of defining space as having properties that could affect objects, especially in the context of dark energy and cosmological expansion.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether space is fixed or moving, with multiple competing views presented throughout the discussion. The nature of space and its properties remains a contested topic, with differing interpretations of Einstein's work and the implications of cosmological expansion.

Contextual Notes

Participants highlight limitations in defining space and motion, particularly regarding the assumptions made about the properties of space and the context in which motion is discussed. The discussion reflects a range of interpretations of theoretical concepts without resolving the underlying uncertainties.

  • #31
heusdens said:
What about virtual particles? Is it possible to measure their momentum during their short lifespan? Isn't that measured momentum an indication of how fast the observer moves relative to the background?

I did not think of that. (Presuming you are responding to my post.) I wonder if the data collected at the LHC and CERN and maybe others is sufficiently accurate to make those calculations. Have they mined their data to search to subtle differences that depend on the month of the year and time of day.

There is a major question along that line. Are the detectors lined up so the path of the particles is parallel with the motion of the Earth around the sun? Remember, we are going about 66,000 mph in our planetary orbit. We might even add that to our galactic orbital speed. Does anyone know what that is?

Who might we ask to check it out?

Excellent thought.

Edit, I just found that speed here:
http://en.wikipedia.org/wiki/Milky_Way#Velocity"
Another reference frame is provided by the cosmic microwave background (CMB). The Milky Way is moving at around 552 km/s[8] with respect to the photons of the CMB, toward 10.5 right ascension, -24° declination (J2000 epoch, near the center of Hydra).
 
Last edited by a moderator:
Space news on Phys.org
  • #32
heusdens said:
What about virtual particles? Is it possible to measure their momentum during their short lifespan? Isn't that measured momentum an indication of how fast the observer moves relative to the background?

I think that you can't do that. Measuring would imply some energy transfer, and that would be free lunch.

Edit:
Even if you measure virtual particle and with that measurment make it real, uncertainty in their energy and momentum would make it impossible to draw any results.
 
Last edited:
  • #33
Hi bkelly,

2) - I'm sure you missed that the concept of simultaneity is important here, as well as the construction of the trolley.
5) - No, they'll measure 1/(1-v²) instead, at least if the trolley works as I think it does. Has to do with simultaneity.
6) "Where the 1 in the equation is the one meter distance between the two markers." - This is awful. Even as an engineer, you should keep track of units. The other results are changed accordingly to the change in 5).
11) - Why would he expect 0.866 m? The trolley made its marks on moving ground, why shouldn't there be a difference?
13) - Not absolute speed. Speed relative to Sally, of course.
"Sally is there only to provide a frame of reference external to Tom." - Sally is also the reference for the alleged "absolute speed". Without Sally, where would the trolley make its marks?
 
  • #34
Ich said:
- I'm sure you missed that the concept of simultaneity is important here, as well as the construction of the trolley.

I do not see where simultaneity plays a role. There is only one event of importance at a time and no causality or effect between any two events in my discussion. Everything happens in only one place. The construction of the trolley is irrelevant. It is not possible to make such a trolley and it used to convey a concept. In a discussion such as this no one expects a real trolley to be constructed.

5) - No, they'll measure 1/(1-v²) instead, at least if the trolley works as I think it does. Has to do with simultaneity.

6) "Where the 1 in the equation is the one meter distance between the two markers." - This is awful. Even as an engineer, you should keep track of units. The other results are changed accordingly to the change in 5).

You are right. That was bad. I had the equation incorrect. I cannot find the same page again, but I did find a Wiki page on length contraction here: http://en.wikipedia.org/wiki/Length_contraction
I have corrected the error and added the page reference.
However, because of the manner in which I misread the equation and happened to get lucky, and the length happened to be 1, it all worked out correctly.

11) - Why would he expect 0.866 m? The trolley made its marks on moving ground, why shouldn't there be a difference?

Item 2 says specifically that the fence is stationary with Sally and with respect to Tom When Sally stops his motion. The fence does not move.

13) - Not absolute speed. Speed relative to Sally, of course.

Yes, absolute speed. Tom made his determination without referencing Sally. Tom was unaware of Sally and unaware of his movement until the measurements were observed to contradict the expectation.

For easy reference, the essay is here:
http://bkelly.ws/space_time/double_observation.htm"
 
Last edited by a moderator:
  • #35
I do not see where simultaneity plays a role. There is only one event of importance at a time and no causality or effect between any two events in my discussion.
As I said, you're obviosly untrained in relativity, so you're unaware of all the pitfalls there are if you define your experiments sloppily.
First thing you have to know is the definition of an event: An event is not simply something happening at a specific time. It is something happening at a specific time and at a specific position. An event cannot happen at two positions.
So there are three events that are important for the function of the trolley:
As the trolley passes immediately in front of Tom the trolley puts a pair of marks on the fence in front of Tom.
"As the trolley passes immediately in front of Tom" - obiously when the midpoint of the trolley passes a certain position, say the zero position.
"the trolley puts a pair of marks on the fence in front of Tom." - That's two events:
1) the trolley marks a point to the left of Tom.
2) the trolley marks a point to the right of Tom.
These are different events, as they happen at different positions.

Then, there is a statement of simultaneity:
"As the trolley passes..."
Which implies that all three events are simultaneous. Now there is the question in which frame they are simultaneous. As it is the trolley that does the marking, it seems natural to assume that the events are simultaneous in its frame. If so, your formula and numbers are incorrect and have to be replaced by the one I posted.

Further, there is a cause-effect relation implied that cannot be maintained: If all three events are simultaneous in one frame, they cannot cause each other. So if the midpoint of the trolley states that it is now exactly in front of Tom, how does it trigger the markers instantaneously? They are each half a meter away.
So you have to arrange beforhand that the markers are triggered at the correct time to circumvent the problem.

Ok, this was just your #1.
Do you understand so far what I'm talking about?
Can you derive the formula I gave you for the separation of the marks if they are marked simultaneously in the trolley's frame?
Just ask if you need help at one point or another, these things are notoriously difficult in the beginning.
Ich said:
11) - Why would he expect 0.866 m? The trolley made its marks on moving ground, why shouldn't there be a difference?

Item 2 says specifically that the fence is stationary with Sally and with respect to Tom When Sally stops his motion. The fence does not move.
If "the fence is stationary with Sally and with respect to Tom when Sally stops his motion", it is obviously moving wrt Tom as long as Tom is moving wrt Sally. So Tom sees the trolley mark a moving fence.
 
Last edited:
  • #36
Calimero said:
I think that you can't do that. Measuring would imply some energy transfer, and that would be free lunch.

Edit:
Even if you measure virtual particle and with that measurment make it real, uncertainty in their energy and momentum would make it impossible to draw any results.

I see, thanks.

But what about this Hawking radiation of a black hole (caused by an infalling virtual particle while the counterpart anti-matter particle stays outside of the horizon and causi drains energy from the black hole) would that radiation have any deviation depending on how fast the black hole is moving relative to the (supposed) fixed space background?
 
  • #37
No. For a Schwarzschild BH temperature is T= 1/8pi*M (in units C=G=1), so obviously it does not depend from 'motion relative to background'.

I think that CMB is best reference we will ever have. Although it has no special meaning in terms of physics (it is special only for our convenience), it can tell us how is something moving (or not) relative to the ancient matter, or simply with respect to the 'bulk of the universe'.
 
  • #38
Calimero said:
No. For a Schwarzschild BH temperature is T= 1/8pi*M (in units C=G=1), so obviously it does not depend from 'motion relative to background'.

I think that CMB is best reference we will ever have. Although it has no special meaning in terms of physics (it is special only for our convenience), it can tell us how is something moving (or not) relative to the ancient matter, or simply with respect to the 'bulk of the universe'.

So the CMB is in fact some 'absolute' preferred intertial reference frame, although acc. to SR such should not exist?
 
  • #39
I think this is beginning to hijack the original purpose of this thread. I hope you don't mind, but I will start a new thread in Special and General Relativity area.
 
  • #40
heusdens said:
So the CMB is in fact some 'absolute' preferred intertial reference frame, although acc. to SR such should not exist?
No, it is not. It is a nice, convenient reference frame that has no special significance to SR.
 

Similar threads

Undergrad Dark Energy as repulsive gravity
  • · Replies 6 ·
Replies
6
Views
2K
Undergrad Dark energy is intrinsic to the space itself
  • · Replies 5 ·
Replies
5
Views
2K
Undergrad Why is the observed local region of space flat?
  • · Replies 25 ·
Replies
25
Views
3K
Undergrad What if the Universe expands faster than the speed of light?
  • · Replies 19 ·
Replies
19
Views
5K
Undergrad Is this explanation of "space itself expanding" correct?
  • · Replies 27 ·
Replies
27
Views
4K
Undergrad The CMB drag on an object moving through space
  • · Replies 6 ·
Replies
6
Views
2K
High School What does it mean to say the Universe is the same everywhere?
  • · Replies 8 ·
Replies
8
Views
2K
Graduate Alternative topology of our 3D space
  • · Replies 1 ·
Replies
1
Views
2K
Undergrad Cosmological principle about space and time
  • · Replies 20 ·
Replies
20
Views
2K
Undergrad Question about geometrical engineering (placeholder name)
  • · Replies 32 ·
2
Replies
32
Views
2K