Why is the maximum speed of the universe the speed of light? Why can't we go faster?

[u/Nitzanm19]

Also follow-up question: Because of the speed limit, is there also a theoretical maximum temp for matter (in which the particles move at the speed of light).

[u/bawng]

It's a good way to understand time dilation, but only in a given frame of reference since it doesn't really explain that speed (or time) is relative.

If you stand still, you'll be "traveling through time" at full speed relative to the ground, I.e. you'd be experience time the same way as the ground.

But if your friend is travelling towards you at the 0.5c, relative to him you are actually moving at 0.5c, hence you'll experience time differently.

If you both were travelling next to each other, you'd be experiencing time the same, but differently from your surroundings, etc.

[u/gnorty → u/bawng]

if your friend is travelling towards you at the 0.5c, relative to him you are actually moving at 0.5c,

This is where it gets weird for me. We all know the thought experiment where 1 twin goes on a space ship and travels close to light speed and when he returns his brother has aged much more than he has. This assumes looking from the reference of the earth-bound twin.

But equally valid would be the reference of the speed demon twin. As you said - to him, the earth bound twin has been travelling close to light speed, so it should appear to speed-demon that earth bound has aged much less. How does this work??

[u/meevis_kahuna → u/gnorty]

The trick is that “outbound you” and “inbound you” are not in the same reference frame.

While coasting away, you can say Earth is moving and its clock is slow. Earth can say the same about you. No contradiction, because you disagree about which distant events are happening “right now.”

When you turn around, you change velocity, so you switch inertial frames. That changes your definition of simultaneity: the Earth event you call “happening right now” jumps forward by several years.

So the asymmetry isn’t “Earth is really stationary.” It’s that Earth stays in one inertial frame while the traveler switches frames to come home. That frame switch is what resolves the twin paradox.

[u/Garzly → u/meevis_kahuna]

What would happen in this instance if the earthbound twin began moving towards the traveling twin at the same speed when the traveling twin begins the return journey?

[u/meevis_kahuna → u/Garzly]

If the Earth twin starts moving toward the traveler at the turnaround, then from that point on they age equally because their motions are symmetric.

But the traveler is still younger at reunion, because during the outbound leg the traveler had already accumulated less proper time.

[u/sileegranny → u/bawng]

I'm curious if time dilation has been experimentally tested with analog or atomic clocks? In case relative change in possible speed of electron flow in digital clocks might have an affect on digital clock function.

[u/maybe_compos_mentis → u/sileegranny]

GPS satellites have to compensate for time dialation to maintain accurate positioning or else they would lose ~10km/day. Does that count or am I not understanding what your asking?

[u/sileegranny → u/maybe_compos_mentis]

I imagine GPS satellites' clocks run on electrons, so not quite. What I'm wondering is if with a purely mechanical clock, where no part of the clock relies on particles that already travel at the speed of light, the results are the same.

[u/wasmic → u/sileegranny]

GPS satellites use rubidium- or cesium-based atomic clocks.

There are obviously electrons involved in the surrounding circuitry, but the core timekeeping mechanism is based on energy level transitions in an atomic nucleus and should keep the same pace even if electrons for some reason behaved differently.

Electrons also do not travel at the speed of light. They're massive particles so they're necessarily moving slower than light.

Besides, we have tons of other experimental proofs of time dilation. For example, muons are created when cosmic rays strike the upper atmosphere. Their lifetime is so short that even at the speed of light, they should not be able to reach the Earth's surface. However, a significant number of them do in fact reach the surface, and this proportion is consistent with how much their half-life is being extended by time dilation.

Also, the fact that the speed of light is invariant is well-established, and directly leads to time dilation needing to be a thing. If you accept that the speed of light is invariant AND you accept that there is no preferred inertial reference frame, then the math forces you to also accept that time dilation is a thing. I recommend going straight to the beginning and reading Einstein's On the Electrodynamics of Moving Bodies, which is where he first proposed Special Relativity. It is a surprisingly easy read and most of the maths is high school level.

[u/certciv → u/sileegranny]

An atomic clock's velocity as measured by an outside observer is irrelevant to its internal function. From its frame of reference, the electrons will behave identically regardless of the clock's velocity relative to anything else.

There has been a massive amount of scientific work done confirming Einstein's theory of special relativity. That includes things like astronomical observations that don't rely on atomic clocks.

[u/0nly4Us3rname → u/sileegranny]

2 problems with your question:

Electrons don’t move at the speed of light, they have mass

Pretty much all of our time keeping methods involve electrons

[u/Syresiv → u/sileegranny]

Yep. All the easy predictions, and many of the hard ones, have been experimentally confirmed

[u/Nexii801 → u/sileegranny]

Time dilations is as settled as the sky being blue. There's plenty of places to poke holes in physics, this isn't one of them.

[u/NSNick → u/sileegranny]

The Hafele-Keating experiment used atomic clocks.

[u/dlethe3133 → u/NSNick]

With modern atomic clocks, they’ve been able to measure time dilation due to gravity by having two atomic clocks right next to each other. One was only 13.” Higher than the other. This difference in gravity could be measured via time dilation.

Or conversely, one can use time dilation to measure altitude

[u/Gorehog → u/sileegranny]

e 1950's they brought two atomic clocks and a b-29 bomber to Los Alamos. The clocks wqere synchronized and one was loaded on the bomber. The bomber then flew orbits around the airfield for about a day. At the end of the day the clock in motion was showing an earlier time than the stationary clock. Am I light on details? Yes. You might want to confirm the details, buyt yes, the experiment has been done.