Cassini Experiment Confirms General Relativity

MikeZilla writes "An experiment by Italian scientists using data from NASA's Cassini spacecraft, currently en route to Saturn, confirms Einstein's theory of general relativity with a precision that is 50 times greater than previous measurements."

Comments

Help Me Here--some novice Questions

[jazman_777]

It seems that, according to scientific philosophy today (and I say this as an observer, not a scientist), you still can't really believe this is _the_ truth about something. You have to keep thinking, "it might _not_ be true". I hear how a hypothesis must be "falsifiable"--what does that mean? So if science is a search for truth, how can you find it? And how does this experiment matter? I mean, didn't people already believe that relativity was (mostly, apparently, seemingly) true?

Re:Help Me Here--some novice Questions

[Unholy_Kingfish]

Scientists know that there is always more. Once you find an answer to a question, you will open to the door to 3 more questions about something else. It is the way advances are made. You create a theory, which you test, and from those results you come up with more theories.

With this particular test, they wanted to rerun test that have been run before to see if the results from the Viking Mission hold up with the more accurate equipment available now.

Truth is only as good as the information you have. At first there was earth wind fire and water (no jokes please). Then there were atoms. Then the atoms where broke down to electrons proton and neutrons. Then those particles where broke down into quarks. Then quarks where broke down into mueons. Each time, they add to the new truth.

The fundamental philosophy of that truth doesn't change, just the details showing it is.

Re:Help Me Here--some novice Questions

[deglr6328]

"It seems that, according to scientific philosophy today (and I say this as an observer, not a scientist), you still can't really believe this is _the_ truth about something. You have to keep thinking, "it might _not_ be true"."

I think basically that's right, it's just a matter of what theories we decide to keep testing to the limit to try to find any inconsistencies. For instance, when a new method of atomic mass spectroscopy is invented no one says 'hey I bet we could use this to test Dalton's theory of atoms down to the fraction of an AMU!', even though it could very well be used to do that. The reason we don't is because no one expects to find anything that would invalidate the atomic theory of elements. We know, however, that there must be something "beyond" Einstein's relativity in the same way that the orbit of mercury reveals a breakdown of Newtonian Physics. This experiment with Cassini was in a way looking for Einstein's 'Mercury problem'. The fact that it has not found any inconsistency with GR (along with countless other experiments done in the past century) is a testament to, not only our lack of tools to measure with extreme enough precision the physical phenomena effected by GR but also to the greatness of the theory of General Relativity itself. We will continue to test Einstein though, in December Gravity Probe B will be launched, using ultrahigh precision quartz sphere gyroscopes, it will be able to measure certain effects of GR to the parts per million range. Science is a search for ever greater truth.

Re:Help Me Here--some novice Questions

[UnknownSoldier]

> You create a theory, which you test, and from those results you come up with more theories.

You left off the first bit! You *first* observe. Theory did not come first! It came from observations, and wondering how the universe works.
e.g.

1. Observe (natural, or man-made expirements)
2. Theorize
3. Test
repeat

> Truth is only as good as the information you have.

Physical truth, yes. Meta-physical truth, I disagree. But that is a discussion for another time.

Truth doesn't change, but your perception and knowledge of it does.

Cheers

--
"I want to move to theory, everything works in theory." - John Cash

Cute, but

[CheshireCatCO]

Nice measurement, no doubt. But the article is a bit misleading. This isn't the most precise measurement of GR, just the most precise mesurement of this prediction. It sounds like they got this measurement to an error of one part per fifty thousand. If memeory serves, the measurements of the orbit on pulsar 1933+16 (the one that netted Taylor and Hulse the Nobel Prize about a decade ago) are precise to one part in something lik ten to the eleventh. And they agree with GR.

One some level it amazes me that GR passes every test we throw at it with such flying colors. On another level, I agree with Albert: the theory is too beautiful *not* to be true.

Re:Theory

[Narchie Troll]

That's not really true. "Law" is something of a layman's term. In mathematics and science, there are no absolute facts, just postulates and theorems. General relativity is basically identical to Newton's theory of gravity in basic situations, but it differs when you're working with high speeds and large scales. In fact, Newtonian physics is proven wrong for many planetary-scale gravitational effects.

It's a "law" because it seems immovable to us.

Re:Theory

[Alsee]

What a lot of people don't seem to know is that the fact that it is still called the 'theory' of relativity means that it hasn't been accepted as gospel by scientists yet.

That's not a very good description of the situation.

Contrast this with the 'law' of gravity, which has.

Actually the 'law' of gravity have been proven incorrect. It has been superceded by relativity. The common usage of 'theory' and 'law' don't quite match up with the scientific usage :)

According to the "law of gravity" the results from this measurement should have been zero. Relativity says the value isn't zero, and the value given by relativity is at least a 99.998% match for the measured value. The remaining 0.002% doesn't indicate a problem with relativity, it is just the limit of the accuracy of devices they used to make the measurement.

Relativity has been challenged with the most stringent scientific testing ever devised in countless ways. Actually part of the "problem" is that relativity is "too good". Absolutely everything it describes it does so with unbelievable accuracy. The irony is that you can't learn anything new when every single measurements exactly matches your predictions. It leaves them without anything to grab on to to try to explore the things that relativity doesn't explain.

-

Re:Theory

[Scarblac]

There's no difference between a "theory", a "theorem", a "law", etc in science. They're all just synonyms for theory, to give them different names. Science deals with theories. Math deals with theorems.

I've remarked before, it's only Americans that have this idea that a "law" is better than a "theory", etc.

Can someone explain to me why that is? Is this taught in schools? Is it caused by Creationists (another US phenomenon) trying to muddy the waters by suggesting "evolution theory" hasn't made it to "law status" yet?

the usual misstatement

[penguin7of9]

It's misleading to say that this experiment "confirms" General Relativity. What it does is fail to falsify GR. That's nothing to sneeze at. But it tests such a small part of GR that one really can't say that it "confirms" GR. These kinds of delays are part of many alternative theories as well. If you say that this experiment "confirms" GR, then it also "confirms" many theories that otherwise wildly disagree with GR.

Re:Theory

[00420]

I've remarked before, it's only Americans that have this idea that a "law" is better than a "theory", etc.
Can someone explain to me why that is? Is this taught in schools?

Yes. I was tought this in middle school. I was told the steps of the Scientific Method were:
1. Observe
2. Hypothosize
3. Experiment
4. Theory
5. More experiments
6. Law

Not only that but I was told that in order for something to become a law it had to hold up 100% of the time!

I was quite suprised when I got to college and learned that this was not true.