7 ms·

Physicists used atomic clocks to test the theory of general relativity

56 points by SQL2219 8y ago

aks232 8y ago
That was more interesting than I expected! Good to test basic assumptions otherwise taken for granted
- ravar 8y ago
  General relativity is not a basic assumption in physics. There is a large feeling that there is something more out there , but that we don't really know what it is . Some theories of dark energy or dark matter work by modifying gravity away from general relativity and in the process create testable predictions.
  - philipov 8y ago
    I believe that modified theories of gravity are stuck on modifying Newtonian dynamics, and their inability to make the jump to modified GR is why they are still disfavored compared to the dark matter hypothesis.
    - whatshisface 8y ago
      There are modified GR theories[0][1]. [0]http://adsabs.harvard.edu/abs/1988PhLB..202..497B http://adsabs.harvard.edu/abs/1988PhLB..202..497B [1]http://xxx.lanl.gov/abs/astro-ph/9612099 http://xxx.lanl.gov/abs/astro-ph/9612099
      - philipov 8y ago
        Are they able to explain the Bullet Cluster?
        voice_of_reason 8y ago
        "It might sound like a story from a parallel universe – but it’s true. The Bullet Cluster isn’t the incontrovertible evidence for particle dark matter that you have been told it is. It’s possible to explain the Bullet Cluster with models of modified gravity. And it’s difficult to explain it with particle dark matter" https://backreaction.blogspot.com/2017/01/the-bullet-cluster-as-evidence-against.html https://backreaction.blogspot.com/2017/01/the-bullet-cluster...
        acqq 8y ago
        Still: https://medium.com/starts-with-a-bang/only-dark-matter-and-not-modified-gravity-can-explain-the-universe-e272e5f64707 https://medium.com/starts-with-a-bang/only-dark-matter-and-n... "Modified gravity cannot successfully predict the large-scale structure of the Universe the way that a Universe full of dark matter can. Period. And until it can, it’s not worth paying any mind to as a serious competitor. You cannot ignore physical cosmology in your attempts to decipher the cosmos, and the predictions of large-scale structure, the microwave background, the light elements, and the bending of starlight are some of the most basic and important predictions that come out of physical cosmology. "
        voice_of_reason 8y ago
        And the quote war goes on :) Mr Siegel asserts that dark matter hypothesis is better than any kind of MOND (and, may I add, his opinion is expressed in over-confident and even dogmatic way) because it can "explain" structure of the Universe. However, people in comments doubt that LCDM is particularly good in this area: "The problem is that dark matter can’t predict the structure of the universe all that well either. Making those dark matter simulations work requires introducing all sorts of epicycles, kludgy mechanisms to make the calculations work out properly. I’m not a big MOND fan, but MOND seems to solve certain problems fairly well, and the galaxy rotation problem is one of them." https://medium.com/@kaleberg7/the-problem-is-that-dark-matter-cant-predict-the-structure-of-the-universe-all-that-well-either-7aae885fc5db https://medium.com/@kaleberg7/the-problem-is-that-dark-matte...
      - qubex 8y ago
        Let’s also not forget Einstein-Cartan theory that takes torsion into consideration and associates it with quantum spin, producing some very satisfying predictions for general cosmology and might even account for the discrepancy in galactic rotations while not causing disruption on the scales we have tested GR so far. http://iopscience.iop.org/article/10.3847/0004-637X/832/2/96/pdf http://iopscience.iop.org/article/10.3847/0004-637X/832/2/96...
  - JumpCrisscross 8y ago
    > There is a large feeling Feelings don’t count in science. Every experiment (I am aware of) to disprove GR has failed. It is the best explanation of spacetime we have.
    - whatshisface 8y ago
      It is better than a feeling. GR cannot be quantitized. If anyone describes the present status of gravity as anything other than a mystery that we are good at predicting the movements of, they are wrong.
      - JumpCrisscross 8y ago
        > GR cannot be quantitized This is irrelevant. GR makes accurate predictions. Perhaps we haven’t figured out how to quantise it. Maybe it isn’t a quantum field. Maybe we’re mis-interpreting the mathematics. Hypotheses are interesting. I find the variable speed of light discipline neat. But they’re just hypotheses. Until they explain experimental evidence better than GR, they will remain hypotheses.
        TheOtherHobbes 8y ago
        It's not irrelevant if you're looking for new classes of predictions and new kinds of experiments - which is one of the motivations for quantum gravity.
Simon_says 8y ago
> The concept they tested is similar to Galileo’s apocryphal experiment, in which he dropped two objects of the same mass off the Leaning Tower of Pisa and found that they fell at the same acceleration regardless of their composition. Typo. Should say of different masses.
dghf 8y ago
Quibble: the article refers several times to the theory of general relativity. I always thought it was the general theory of relativity: i.e., it was the theory itself that was general, handling everything the special theory (limited to inertial reference frames) couldn't. Am I making a distinction without a difference? Are there two forms of the name in free variation?
- kvakkefly 8y ago
  They are just somewhat different names of the same thing. General relativity includes the special relativity one where special means without accelerated reference frames, i.e. nothing accelerates or is exposed for gravity.
  - moefh 8y ago
    > special means without accelerated reference frames That's something a lot of people say, but it's not strictly true. Special Relativity is fully capable of describing acceleration in a flat (Minkowski) spacetime[1]. General Relativity is only really needed when there's curvature in the spacetime (gravity). [1] https://en.wikipedia.org/wiki/Acceleration_(special_relativity) https://en.wikipedia.org/wiki/Acceleration_(special_relativi...
- JumpCrisscross 8y ago
  > Quibble: the article refers several times to the theory of general relativity “General relativity...[is] also known as the general theory of relativity or GTR“ [1]. Einstein himself wrote of der allgemeinen Relativitätstheorie. [1] https://en.m.wikipedia.org/wiki/General_relativity https://en.m.wikipedia.org/wiki/General_relativity
dghughes 8y ago
>“We’ve moved the lab 14 times around the sun,” says Patla. He’s not trying to be cute; it turns out that Earth moves through some distinctive regions in space. Because Earth’s orbit isn’t a perfect circle—its distance from the sun varies—the clock moved through varying gravitational fields. Michael from Vsauce has a nice graphic showing that https://youtu.be/IJhgZBn-LHg?t=1016 https://youtu.be/IJhgZBn-LHg?t=1016
z3t4 8y ago
My theory is that time runs backwards.

56 points by SQL2219 8y ago

aks232 8y ago

That was more interesting than I expected! Good to test basic assumptions otherwise taken for granted

ravar 8y ago
General relativity is not a basic assumption in physics. There is a large feeling that there is something more out there , but that we don't really know what it is . Some theories of dark energy or dark matter work by modifying gravity away from general relativity and in the process create testable predictions.
- philipov 8y ago
  I believe that modified theories of gravity are stuck on modifying Newtonian dynamics, and their inability to make the jump to modified GR is why they are still disfavored compared to the dark matter hypothesis.
  - whatshisface 8y ago
    There are modified GR theories[0][1]. [0]http://adsabs.harvard.edu/abs/1988PhLB..202..497B http://adsabs.harvard.edu/abs/1988PhLB..202..497B [1]http://xxx.lanl.gov/abs/astro-ph/9612099 http://xxx.lanl.gov/abs/astro-ph/9612099
    - philipov 8y ago
      Are they able to explain the Bullet Cluster?
      - voice_of_reason 8y ago
        "It might sound like a story from a parallel universe – but it’s true. The Bullet Cluster isn’t the incontrovertible evidence for particle dark matter that you have been told it is. It’s possible to explain the Bullet Cluster with models of modified gravity. And it’s difficult to explain it with particle dark matter" https://backreaction.blogspot.com/2017/01/the-bullet-cluster-as-evidence-against.html https://backreaction.blogspot.com/2017/01/the-bullet-cluster...
        acqq 8y ago
        Still: https://medium.com/starts-with-a-bang/only-dark-matter-and-not-modified-gravity-can-explain-the-universe-e272e5f64707 https://medium.com/starts-with-a-bang/only-dark-matter-and-n... "Modified gravity cannot successfully predict the large-scale structure of the Universe the way that a Universe full of dark matter can. Period. And until it can, it’s not worth paying any mind to as a serious competitor. You cannot ignore physical cosmology in your attempts to decipher the cosmos, and the predictions of large-scale structure, the microwave background, the light elements, and the bending of starlight are some of the most basic and important predictions that come out of physical cosmology. "
        voice_of_reason 8y ago
        And the quote war goes on :) Mr Siegel asserts that dark matter hypothesis is better than any kind of MOND (and, may I add, his opinion is expressed in over-confident and even dogmatic way) because it can "explain" structure of the Universe. However, people in comments doubt that LCDM is particularly good in this area: "The problem is that dark matter can’t predict the structure of the universe all that well either. Making those dark matter simulations work requires introducing all sorts of epicycles, kludgy mechanisms to make the calculations work out properly. I’m not a big MOND fan, but MOND seems to solve certain problems fairly well, and the galaxy rotation problem is one of them." https://medium.com/@kaleberg7/the-problem-is-that-dark-matter-cant-predict-the-structure-of-the-universe-all-that-well-either-7aae885fc5db https://medium.com/@kaleberg7/the-problem-is-that-dark-matte...
    - qubex 8y ago
      Let’s also not forget Einstein-Cartan theory that takes torsion into consideration and associates it with quantum spin, producing some very satisfying predictions for general cosmology and might even account for the discrepancy in galactic rotations while not causing disruption on the scales we have tested GR so far. http://iopscience.iop.org/article/10.3847/0004-637X/832/2/96/pdf http://iopscience.iop.org/article/10.3847/0004-637X/832/2/96...
- JumpCrisscross 8y ago
  > There is a large feeling Feelings don’t count in science. Every experiment (I am aware of) to disprove GR has failed. It is the best explanation of spacetime we have.
  - whatshisface 8y ago
    It is better than a feeling. GR cannot be quantitized. If anyone describes the present status of gravity as anything other than a mystery that we are good at predicting the movements of, they are wrong.
    - JumpCrisscross 8y ago
      > GR cannot be quantitized This is irrelevant. GR makes accurate predictions. Perhaps we haven’t figured out how to quantise it. Maybe it isn’t a quantum field. Maybe we’re mis-interpreting the mathematics. Hypotheses are interesting. I find the variable speed of light discipline neat. But they’re just hypotheses. Until they explain experimental evidence better than GR, they will remain hypotheses.
      - TheOtherHobbes 8y ago
        It's not irrelevant if you're looking for new classes of predictions and new kinds of experiments - which is one of the motivations for quantum gravity.

Simon_says 8y ago

> The concept they tested is similar to Galileo’s apocryphal experiment, in which he dropped two objects of the same mass off the Leaning Tower of Pisa and found that they fell at the same acceleration regardless of their composition. Typo. Should say of different masses.

dghf 8y ago

Quibble: the article refers several times to the theory of general relativity. I always thought it was the general theory of relativity: i.e., it was the theory itself that was general, handling everything the special theory (limited to inertial reference frames) couldn't. Am I making a distinction without a difference? Are there two forms of the name in free variation?

kvakkefly 8y ago
They are just somewhat different names of the same thing. General relativity includes the special relativity one where special means without accelerated reference frames, i.e. nothing accelerates or is exposed for gravity.
- moefh 8y ago
  > special means without accelerated reference frames That's something a lot of people say, but it's not strictly true. Special Relativity is fully capable of describing acceleration in a flat (Minkowski) spacetime[1]. General Relativity is only really needed when there's curvature in the spacetime (gravity). [1] https://en.wikipedia.org/wiki/Acceleration_(special_relativity) https://en.wikipedia.org/wiki/Acceleration_(special_relativi...
JumpCrisscross 8y ago
> Quibble: the article refers several times to the theory of general relativity “General relativity...[is] also known as the general theory of relativity or GTR“ [1]. Einstein himself wrote of der allgemeinen Relativitätstheorie. [1] https://en.m.wikipedia.org/wiki/General_relativity https://en.m.wikipedia.org/wiki/General_relativity

dghughes 8y ago

>“We’ve moved the lab 14 times around the sun,” says Patla. He’s not trying to be cute; it turns out that Earth moves through some distinctive regions in space. Because Earth’s orbit isn’t a perfect circle—its distance from the sun varies—the clock moved through varying gravitational fields. Michael from Vsauce has a nice graphic showing that https://youtu.be/IJhgZBn-LHg?t=1016 https://youtu.be/IJhgZBn-LHg?t=1016

z3t4 8y ago

My theory is that time runs backwards.