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Einstein Was Right: NASA Announces Results of Epic Space-Time Experiment (nasa.gov)
294 points by tableslice on May 20, 2011 | hide | past | web | favorite | 26 comments



It's not all that epic. These effects had already been measured by other experiments and were found to agree with general relativity to much more accuracy than the GP-B measurements. What GP-B brought to the table was a direct measurement, as opposed to indirect measurements used by the other experiments.

However, because the way they measured it pushed the limits of engineering, if GP-B had NOT agreed with GR there is good chance the results would have been dismissed as most likely due to equipment flaws.

While it is in general a good idea to confirm measurements, especially using different techniques, in a case like this where the confirmation will be much less precise than the other experiments and will likely be rejected if it fails to confirm, you have to wonder why this was funded over other projects.

The answer to that turns out to be simple: politics. When space scientists ranked all the proposed missions under consideration, GP-B came in dead last. However, its proponents went to Congress, and got Congress to override the normal process for prioritizing missions, forcing NASA to move it to the front, ahead of more scientifically worthy missions.

There are a lot of very worthwhile scientific missions that we can't fly due to budget limitations. It's a shame to see $750 million of the limited budget go to a mission so far down on the importance list.


An experiment spanning decades and involving the creation of the most perfect spheres created by man can rightly be called epic. Not sure why you're so down on this.

Also I'd be interested in sources, as well as genuinely curious what missions would be more important.


> what missions would be more important

Here is the stack rank of operating missions as of 2008 (when NASA needed to shut down some missions to save money):

1. Swift, 2004

2. Chandra, 1999

3. Galex (Galaxy Evolution Explorer, ultraviolet), 2003

4. Suzaku (X-ray), 2005

5. Spitzer, 2003

6. WMAP (Wilkinson Microwave Anisotropy Probe), 2001

7. XMM-Newton (X-ray Multi-Mirror Mission), 1999

8. Integral (INTErnational Gamma-Ray Astrophysics Laboratory), 2002

9. Rossi X-ray Timing Explorer, 1995

10. Gravity Probe B, 2004

source: http://www.newscientist.com/article/dn13938?DCMP=ILC-hmts...

I also found this read (http://www.skyandtelescope.com/news/121390204.html) very interesting.


Cool, thanks.


An "epic" was originally a very long story in the form of a poem. As an experiment lasting 47 years, this certainly qualifies.


I'm interested in the indirect measurements that have been done. Where could I find more information about them?


They are mentioned in this article: http://www.skyandtelescope.com/news/121390204.html


It is epic because he predicted this before any of the technical wizardry was even in existence.

So, sure - the proof may not be epic -- but the prediction certainly is, especially even moreso that he is correct (again)


Einstein was so brilliant that his very name became a popular cliche. And yet, the more modern science digs into his theories, the more we see that, if anything, his brilliance is still underrated.


The precision they manufactured those things was pretty epic, too.


It's important to realize these predictions were not all separate things - where he just said "Oh hey, what about X?"

He developed mathematical models for currently available observations. Those models in turn also suggested other phenomenon that could not be measured at the time. As time went on, some of these have been measured and found to hold true, others observations about the universe have been had that suggest they don't hold true in all cases (eg: "dark" stuff)



Did the experiment use a control? That is, did they put other gyros in places where space time should not have been twisted and observe no deviation?

If not, how do they know that the deviation was in fact caused by twisting space time?


While I understand your thinking, what you're suggesting is not the correct methodology. General Relativity makes a specific, quantitative prediction for an effect. The prediction is not trivial, in the sense that the most reasonable alternative theory -- Newtonian dynamics -- predicts there should be no effect at all. (This is the null hypothesis if you will.)

The GP-B experiment measured this effect and found agreement with the GR prediction. This does not prove that GR is correct; rather, it is a piece of evidence that implies GR is more likely to be a correct description of gravity than what we previously believed [1]. Because the prediction was quantitative, it is unlikely that the result is caused by something else, which makes the evidence in favor of GR that much stronger.

Now, control groups are often used in life sciences fields. For example when you test a drug, you have a control group that takes placebo. It's not my field but as far as I understand this is done for two reasons. First, there is no quantitative prediction regarding how effective the drug should be, because drugs are not understood so precisely. So the prediction you're testing is much weaker; it's just a boolean. Second, there is a known effect -- the placebo effect -- that can affect results. In other words your null hypothesis is that there may be some effect. These things mean that, without a control group, the evidence in favor of a drug's effectiveness is not very strong.

[1] That is not to say that we believed GR was wrong, but we can never be 100% sure, and every piece of positive evidence strengthens the case.


Right, the efficacy of GR was being tested, and the control was Newtonian dynamics. GR was found to successfully predict the results observed. The control is to attempt to predict the results with Newtonian dynamics and check that that prediction is less accurate.

If you accidentally did an experiment where GR and Newton predict the same thing, the control would kick in and tell you that you hadn't proved anything.


I applaud the perfect precision of the above explanation. One so rarely sees perfectly precise explanations these days.


Beautiful explanation. One thing, though:

  > Second, there is a known effect -- the placebo effect --
  > that can affect results. In other words your null
  > hypothesis is that there may be some effect. These 
  > things mean that, without a control group, the evidence
  > in favor of a drug's effectiveness is not very strong.
Placebo effect is but one confound variable you'll encounter in pharmacological and all other "non-quantitative" prediction experiments. There are plenty of others; for instance, order of measurement, influence of experimenter, subtle pre-existing differences, and so on.

In order to keep confounds in check, scientists attempt to keep everything either equivalent (by matching samples as precisely as scientifically feasible) or randomly distributed (by using, for instance, Latin squares and other randomization techniques).


They don't actually know that the deviation was caused by the twisting of space-time (and neither do we). What they knew before conducting the experiment was that they had a theory (Newton's) which predicted result A, and another theory (Einstein's) which predicted result B.

They perform the experiment and obtain result B. This disproves Newton's theory immediately, and confirms Einstein's theory. We don't know that it is right, only that it has successfully made a prediction about something that hadn't been tested at the time the theory was developed.

Testing a place in space-time that should not be twisted would provide another element of confirmation, however the strongest and most interesting tests are those where the two theories differ in their prediction, not where they agree.


This is a measurement, not an intervention experiment. A control experiment in this case should be performed on another universe with no GR. Of course, i guess they did test it on neutral regions as well. Since are no other known forces acting out there, and the agreement to theory is so remarkable, its fairly conclusive the effect was due to gravity.


WTF? I just got 2 down votes for this? It was a serious question. I want to know, did they take a negative measurement too, and if they didn't, how does this prove relativity?


This experiment did not set out to "prove" anything. I think you'll find that the original article does not use the word "prove" even once.

The experiment set out to experimentally test the accuracy of Einstein's predictions. The results of the experiment showed that under these specific circumstances, the predictions line up extremely well with observations.

There's no "control group" for this kind of test. Of course, they could potentially run multiple experiments to verify Einstein's predictions under different circumstances. That might provide useful information, but the lack of such information in no way discredits the results of this particular experiment.

If you want to read more about the experimental protocol, check out the final results paper: http://arxiv.org/pdf/1105.3456v1


please do not complain about downvoting, it does nothing to contribute to discourse, and litters up the site.


It would be interesting to find out if using Hans Montanus's non-canonical formulation of GR (which involves a Euclidean metric and perfectly flat space-time) would yield the same numerical predictions, just with different "book keeping".

That would put a different spin on the notion of Einstein "being right" as I think a lot of folks subconsciously equate GR with the "strangeness" of the Minkowski metric and non-Euclidean space-time manifold.


From article: "The mass of Earth dimples this fabric, much like a heavy person sitting in the middle of a trampoline."

I will never imagine general relativity the same way again.


My understanding is we should benchmark everything with http://en.wikipedia.org/wiki/Speed_of_light


I initially read this "Einstein was right, announces results of epic space-time experiment", which would have been epic and a much more interesting story.




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