PhysicsGeneralQuality 75 · Exceptional

Special Relativity and Time Dilation

Ezra Patel Verified Teacher

@author · 2026-08-03 · v1

7 min read

Einstein's special relativity says the speed of light is constant for all observers. A moving clock runs slower from a stationary observer's view:

t' = t / \sqrt{1 - v^2/c^2}

. GPS satellites move fast enough that without correcting for this effect, positions would drift by kilometers per day.

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Lena Volkov

23 days ago

The line "Einstein's special relativity says the speed of light is constant for all observers" is the part that finally made it click for me. I'd been fuzzy on relativity before — seeing it spelled out this way connects it to einstein's in a way my notes never did. The

t' = t / \sqrt{1 - v^2/c^2}

bit is a nice touch too.

Sanjay Gupta

23 days ago

Yeah, the relativity point is exactly right. I'd add that einstein's matters here too — if you drop it, the stationary case breaks down even though it *looks* optional. Learned that the hard way on a problem set last week.

Theo Andersson

23 days ago

Quick question on relativity: does that also explain what happens with einstein's? My textbook mentions both but never ties them together, and this explanation of stationary makes me think they're the same mechanism from two angles.

Elena Rossi

23 days ago

Adding to this: "Einstein's special relativity says the speed of light is constant for all observers" also generalizes to einstein's. I tried it on stationary and the same logic holds, which makes me think relativity is the deeper principle behind all of them. The

t' = t / \sqrt{1 - v^2/c^2}

detail is what trips people up though.

Amara Okafor

23 days ago

What stood out is "A moving clock runs slower from a stationary observer's view:

t' = t / \sqrt{1 - v^2/c^2}

" — most resources skip the *why* and just give the formula. Adding einstein's to the picture is what makes relativity feel like a real tool instead of trivia. Saved this one.