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MiloOfCroton
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How could you tell in an experiment which was happening?
You can't. Length Contraction and Time Dilation are Coordinate Effects which depend on which Inertial Reference Frame (IRF) you choose to describe an experiment in. Therefore, in one IRF, Length Contraction may explain what is happening and in another IRF, Time Dilation may explain the exact same scenario. The muon example can be analyzed from the Earth's rest IRF in which Time Dilation explains how the muons with a very short half life can survive long enough to reach the surface of the Earth while in the rest IRF of the muons, Length Contraction of the Earth explains the same scenario since they don't have far to go.MiloOfCroton said:How could you tell in an experiment which was happening?
ghwellsjr said:You can't. Length Contraction and Time Dilation are Coordinate Effects which depend on which Inertial Reference Frame (IRF) you choose to describe an experiment in. Therefore, in one IRF, Length Contraction may explain what is happening and in another IRF, Time Dilation may explain the exact same scenario. The muon example can be analyzed from the Earth's rest IRF in which Time Dilation explains how the muons with a very short half life can survive long enough to reach the surface of the Earth while in the rest IRF of the muons, Length Contraction of the Earth explains the same scenario since they don't have far to go.
MiloOfCroton said:Space contraction/expansion can explain all that motion explains PLUS it explains gravity, thanks to General Relativity.
PeterDonis said:Why do you think this? Can you give a specific example of space contraction/expansion explaining motion? Are you aware that motion can be present in spacetimes that are static (i.e., not contracting or expanding)? Can you give a specific example of space contraction/expansion explaining gravity? Are you aware that gravity can be present in spacetimes that are static?
MiloOfCroton said:I was lead to believe that spacetime curves in order for gravity to happen.
MiloOfCroton said:The way that objects gravitate towards each other is along these curved spacetime lines.
MiloOfCroton said:Furthermore, if the spacetime grid around objects A and B have become curved due to the attraction between them, then the singular spacetime line directly between object A and B will have become shorter. Is that correct?
MiloOfCroton said:To your first and third questions: Is it believed that our universe is static or dynamic?
MiloOfCroton said:If it is believed to be dynamic, then why should it be relevant if motion or gravity can be present in a static spacetime?
I read the definition for proper time, so I know what that sentence technically means, but I have no idea what the implications are. Can you explain that in a little more detail?PeterDonis said:In spacetime, there's a further wrinkle, because one of the dimensions is time. In spacetime, a geodesic, like the path that a freely falling object (one moving solely under the influence of gravity) follows, is the path with the *longest* proper time.
PeterDonis said:No. First, it's often not a good idea to think of the "grid" as being curved; sometimes it can be helpful, but often it isn't, and this is one of the cases where it isn't. It's better to think of geodesics, including the ones that mark out the "grid", as being the "straightest possible" lines in the curved spacetime.
Second, there's no way to make a comparison between the way things actually are, and the way they would have been if gravity weren't present. I know it seems like there ought to be, intuitively, but there isn't; there's no way to collect any experimental data that would tell you how "curving the grid" changes the lengths of lines. All we have are the actual curves in our actual spacetime.
PeterDonis said:Two reasons: first, you made a general statement that "space contraction/expansion" can explain *everything* that "motion" can explain, plus gravity. You didn't limit it to any particular case.
How can you test that system to know that it is static?PeterDonis said:Second, consider the local patch of spacetime around an isolated gravitating body. That local patch of spacetime is static, even though it happens to be within a universe that is, as a whole, dynamic, and the gravity of the isolated body has to be explained without appealing to the overall dynamic nature of the universe. So any explanation of gravity (and motion, for that matter) has to be able to cover static situations as well as dynamic ones.
MiloOfCroton said:I read the definition for proper time, so I know what that sentence technically means, but I have no idea what the implications are. Can you explain that in a little more detail?
MiloOfCroton said:So you're saying that we have no way of knowing because we only have the objects, and we know how far away they are now; we can't create new circumstances without totally changing the system.
MiloOfCroton said:So my idea was that motion does not exist; only space expansion and contraction exists. You say that it cannot be proven
MiloOfCroton said:I counter that it cannot be proven wrong. Is that correct?
MiloOfCroton said:Do you know of a limited set of cases in which motion can be replaced by a dynamic universe?
MiloOfCroton said:How can you test that system to know that it is static?
MiloOfCroton said:I assume you're implying that the isolated body would be at rest
MiloOfCroton said:there are no forces acting on it to move it
MiloOfCroton said:However (as with my point about the universe being dynamic and your point about spacetime never not having gravity), has there ever been a discovery of an isolated body?
MiloOfCroton said:I would assume an isolated body would be impossible. Even if it were, simply us observing it would make it non-isolated.
But how about the comparison of the shape of the famous freely falling ball of coffee grounds in flat space-time vs. falling towards a gravitatiing mass? Or perhaps your statement refers to the FRW model only and not to the Schwarzschild case? Could you kindly explain?PeterDonis said:Second, there's no way to make a comparison between the way things actually are, and the way they would have been if gravity weren't present. I know it seems like there ought to be, intuitively, but there isn't; there's no way to collect any experimental data that would tell you how "curving the grid" changes the lengths of lines. All we have are the actual curves in our actual spacetime.
timmdeeg said:But how about the comparison of the shape of the famous freely falling ball of coffee grounds in flat space-time vs. falling towards a gravitatiing mass?
If it is not falsifiable then it is not science.MiloOfCroton said:I counter that it cannot be proven wrong.
Timespace expansion refers to the concept in cosmology where the universe is expanding and stretching out over time. This expansion is thought to be a result of the Big Bang and is still ongoing. On the other hand, kinetic motion refers to the movement of an object in relation to its position and time. It involves the transfer of energy from one object to another, resulting in motion.
While timespace expansion and kinetic motion may seem like two separate concepts, they are actually related in the sense that both involve movement. However, the scale at which they operate is vastly different. Timespace expansion occurs on a cosmic scale, affecting the entire universe, while kinetic motion occurs on a smaller scale, involving individual objects and particles.
Timespace expansion cannot be directly observed, as it occurs on such a large scale and over long periods of time. However, its effects can be observed through the redshift of light from distant galaxies and the cosmic microwave background radiation. Kinetic motion, on the other hand, can be observed and measured directly through various scientific experiments and observations.
Timespace expansion has little direct effect on our daily lives, as its effects are on a cosmic scale and operate over long periods of time. However, it does play a role in shaping the universe and its evolution. Kinetic motion, on the other hand, is constantly at play in our daily lives, from the movement of our bodies to the motion of objects around us.
Understanding the difference between timespace expansion and kinetic motion is crucial in various fields of science, such as cosmology, physics, and astronomy. It allows us to better understand the fundamental laws that govern the movement of objects in the universe and helps us make predictions about the future of our universe. Additionally, understanding kinetic motion is essential in many practical applications, such as transportation, energy production, and engineering.