Novice Question

I always thought I had a decent grasp on the fundamentals of physics. I got into a discussion about physics yesterday, however, that illustrated for me just how little I actually knew.

While I knew of relativity, I'd always thought that time dilation was simply a mathematical hypothesis. I'm still stunned in the gap in my education that I'd never until yesterday heard of the Hafele–Keating experiment.

Finding out there was empirical evidence to support it was, I think, something akin to having some random jackrabbit hop up and say, "here kid," and hand me a basket filled with colored eggs, jelly beans and chocolates. Honestly, I'm still trying to wrap my head around it.

The other gap in my understanding and thereby my question for those in the know. I'd always thought that the speed of light was understood to be a universal constant. Has Einstein's theory always stated that 'c' was equal to the speed of light in a vacuum?

I time ago also think that enstein reality is unproven until to know that particles live longer and atomic clock in cosmos goes faster

Hi AhmNee,
Not only is there the Hafele-Keating experiment, but there have been experiments with muons that show that their life increases by the amount predicted by relativity when moving close to c.

See: http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/muon.html

As far as c being the speed of light in a vacuum, that is just to say that light does travel at different speeds in different mediums (refraction), but the speed of light in a vacuum is a constant, c.
Ya that same rabbit jumped up and bit me several times reading about relativity. Welcome to the rabbit hole!
Peace,
Ron

I've been following wiki links from the GPS article someone referenced to show that time dilation exists and have starting to find out just how big the gaps in my education have been. I haven't gone to college, sure, but I took physics in high school. I wouldn't expect to have touched more than the tip of the iceburgh but I would have thought I'd have been taught the fundamentals a little better. It's a glass of cold water in the face to find out that the foundations of your reality are wrong (or at least how you understood reality to be).

I love science and I've been reading ravenously since this has been revealed to me ... but man ... I feel like I need to relearn everything.

Thanks for the link, Ron. I'll definitely be checking it out.

If you want a pretty thorough review of the experimental tests of relativity, check out this page. It goes through a lot of experiments, up to ones done very recently.

Many thanks. Coincidentally, I had the page to their physics FAQ open when I checked your link.

One century (almost) has passed since people found the first proofs...

Giving one or two examples always brings the risk that some fool tries to discuss them. The real good reason is that millions people use Relativity on a daily basis to build and operate devices, and it works everytime. There is nothing to prove anymore.

And by the way, evidence for Relativity doesn't need exotic particles, discussable astronomy or inhuman speeds. Take two good clocks, put one on the top of a cathedral or in a car, and observe its pace change. Not even a GPS is needed.

To be fair, you need clocks that can measure time to the nearest nano second to do this.

I was going to question that myself. In the test done by Hafele-Keating using atomic clocks, the clocks were only off by a few billionths of a second, weren't they? How long would the timeframe be if you had a clock at ground level and one in a tower before you'd see a single second difference in them?

Hey All,
Hi AhmNee,
If you go to that hyperphysics site (from the home page) you can follow 'Relativity - Gravitational Time Dilation'. This gives all the formulas for calculating the differences. Just a quick look over, though, will show that your right, as far as the differences involved. I think it quotes something like 1 part in a billion for the center of the Earth to the surface, about 3000Km.
Peace,
Ron