^Err, light does not have mass. Photons are massless particles.

Light seems to be affected by gravity, but in reality gravity bends space-time, and light just around bends with it.

(Tachyons have not been proven to exist. Hypothetical.)

You can look up the equation and put it in a speadsheet, and plug in different speeds to get a feel for the time dilation relative to an observer. The dilation is pretty flat until you get closer to .8c or thereabouts but expecially much closer, iic closer to c. I had anticipated it would be more proportional to speed, but it's not at all. it doesn't get weired until you get close to C. But you wouldn't ever know how weired it was until you got back home, if it was still there that is. I wish I was better at math to understand physics better. Classical physics math is one thing, the rest of it is another animal altogether. You can understand it more deeply the better you are with higher math, otherwise you are deeply limited. But you can make up for it by listening to Philosophers tale to Physicists, which is easier to understand when your goal is to get a basic gist of things.

I've always heard that if you were to leave Earth to colonize another galaxy, when you got there you would find humans already there because they left after you did, but had the better tech so got there quicker.

Crazy stuff to think about.

quote:

Originally posted by 229DAK:
IIRC, they had to adjust GPS calculations to adjust for relativity.

GPS is affected both by lower gravity and speed. The gravity has the effect of speeding up time while speed will slow time. Gravity has the larger effect than speed since satellites travel at a very small fraction of the speed of light.

The funny thing is both SR & GR were both discovered by Einstein.

This message has been edited. Last edited by: Skins2881,

quote:

Originally posted by kkina:

quote:

Originally posted by mrvmax:
So I if I went from east coast to west coast to work at the speed of light, I would get there faster yet still be late for work?

You would arrive at your destination in approximately .02 seconds. Whether you'd be late or not depends on when you started. You would, however, be a tad younger than your co-workers, if that's something.

Question please, which would be worse, the time dilation or the acceleration/deceleration trauma?

quote:

GPS is affected both by lower gravity and speed. The gravity has the effect of speeding up time while speed will slow time.

You are wrong. The more intense gravity is the slower time advances.

At the boundary of a black hole time doesn’t advance at all.

quote:

... affected both by lower gravity ....

I bet you $50 I'm right.

If higher gravity causes slower speeds, explain how lower gravity wouldn't cause the opposite? You said in you reply that a Black causes slower time, what about if you were 100,000 miles away from that Black hole? Does time move slower or faster?

quote:

I bet you $50 I'm right.

I’ll take that bet if you agree to let kkina be the arbiter.

Your position: “The gravity has the effect of speeding up time”.

My position: “The more intense gravity is the slower time advances.”

Game on!

quote:

Originally posted by preten2b:

quote:

Originally posted by kkina:

quote:

Originally posted by mrvmax:
So I if I went from east coast to west coast to work at the speed of light, I would get there faster yet still be late for work?

You would arrive at your destination in approximately .02 seconds. Whether you'd be late or not depends on when you started. You would, however, be a tad younger than your co-workers, if that's something.

Question please, which would be worse, the time dilation or the acceleration/deceleration trauma?

No trauma at all, as you'd be inside a warp bubble. Never feel a thing. Don't you watch Star Trek, man?

quote:

Originally posted by Pipe Smoker:

quote:

I bet you $50 I'm right.

I’ll take that bet if you agree to let kkina be the arbiter.

Your position: “The gravity has the effect of speeding up time”.

My position: “The more intense gravity is the slower time advances.”

Game on!

I want no part of an interstellar conflict!

And besides, I think this is just a semantic misunderstanding. Lower gravity = less gravity.

^^^^
So no bet. However, in support of my position:

“Gravity affects time, causing it to pass slower in stronger gravitational fields. This phenomenon, known as gravitational time dilation, is a consequence of Einstein's theory of general relativity. It means that a clock near a massive object will tick slower than a clock further away from that object. …”

google “how does gravity affect time?”
AI Overview

I think Skins2881 was saying lower (i.e. less) gravity would in effect speed up time, that is relative (there's that word again) to what's happening at the earth's surface. Which is correct.

You're both right since you're saying the same thing. No harm, no foul.

quote:

Originally posted by Expert308:
That's one thing I don't get. How can anything that physically exists, have zero mass? Small enough that we don't have a device sensitive enough to measure it, OK. But zero? That just doesn't seem to make logical sense.

Then again, NOTHING down in that quantum world really makes sense, does it?

To answer your first question, sometimes a photon is a particle, and sometimes it's a wave. It can be both at the same time, and the word "wavicle" was coined therefor.

I want to apologize for my first posting in this thread. Of course I meant to type neutrino rather than neutron. The fact that neutrino does have a infinitesimal mass escaped me, I should have said anti-photon, the antimatter corresponding particle/wavicle to the photon.

That the universe appears to be expanding faster than the speed of light implies that we will never be able to see it all no matter what technical advancements we attain.

"Warp drive" is a fine plot device, but unlikely to ever be a real thing (as we currently understand physics).

Most Physicists believe that nobody actually understands physics. Some believe we never will.

quote:

"Warp drive" is a fine plot device, but unlikely to ever be a real thing (as we currently understand physics).

I hope Miguel Alcubierre didn't hear you say that!

quote:

Originally posted by bendable:
"It is speed that matters in relation to time, not distance." -fly sig


To me the word speed indicates travel and whenever travel is mentioned I think distance.

Unless you're from Wisconsin. How far is it from A to B? People from Wisconsin will answer with a measure of time like 15 minutes.

Driving from east to west across Texas - it's measured in light-years.

quote:

Originally posted by kkina:
I think Skins2881 was saying lower (i.e. less) gravity would in effect speed up time, that is relative (there's that word again) to what's happening at the earth's surface. Which is correct.

You're both right since you're saying the same thing. No harm, no foul.

Bingo, close to large mass slower, further from mass faster relatively.

Pipe Smoker, I wasn't disputing the science that you mentioned. I was pointing out that what you said proved what I said, yet you said I was wrong which makes no sense.

Think it out, you agree that closer to a black hole time moves slower, what happens as you move further away?

^^^^
From your July 16, 2025 07:37 PM post in this thread:

“GPS is affected both by lower gravity and speed. The gravity has the effect of speeding up time while speed will slow time.”

But, in fact, time is slowed by both speed and gravity. It appears that you’re now agreeing with me.

quote:

GPS is affected both by lower gravity and speed.

There's actually less gravity in space than on earth. That's why the people in the funny suits float.

Google it. Nothing I have said is inaccurate.

## The Impact of Gravity and Speed on GPS Satellites Relative to Earth

Both **gravity** and **speed** (velocity) cause clocks on GPS satellites to run at a different rate compared to clocks on Earth. This is a direct result of Einstein’s theories of general and special relativity, which play a crucial role in the accuracy of the Global Positioning System.

### 1. Effect of Gravity (General Relativity)

- **Weaker Gravity at GPS Altitude**: GPS satellites orbit approximately 20,000 km above Earth, where the gravitational field is weaker than at Earth's surface.
- **Time Runs Faster**: According to general relativity, clocks in weaker gravitational fields tick *faster* than those in stronger fields. Thus, a GPS satellite’s onboard atomic clock ticks faster than a clock at ground level.
- **Magnitude**: The gravity difference causes the satellite clock to gain about **45 microseconds per day** relative to an Earth-based clock[1][2][3].

### 2. Effect of Speed (Special Relativity)

- **High Orbital Speed**: GPS satellites move at about 3,874 meters per second (almost 14,000 km/h).
- **Time Runs Slower**: According to special relativity, moving clocks tick *slower* compared to stationary ones, so the satellite’s clock ticks slower than a stationary clock on Earth because of its orbital speed.
- **Magnitude**: The velocity effect causes the satellite clock to lose about **7 microseconds per day** relative to an Earth-based clock[1][2][3].

### 3. Net Relativistic Effect

- **Combined Result**: The gravitational effect (speeding up) and the velocity effect (slowing down) combine, but gravity’s effect is dominant.
- **Net Gain**: Overall, GPS satellite clocks tick about **38 microseconds per day faster** than clocks on Earth’s surface ([45 - 7 = 38 microseconds])[1][2][3].

| Effect | Change in Time (per day) | Direction |
|--------------------|-------------------------|-----------------------|
| Gravity | +45 microseconds | Clocks tick faster |
| Speed (Velocity) | -7 microseconds | Clocks tick slower |
| **Net Effect** | **+38 microseconds** | **Clocks tick faster**|

### 4. Practical Implications

- **Importance**: Without accounting for these relativistic effects, GPS accuracy would be lost within minutes, and positioning errors would accumulate at a rate of about 10 km per day[1][3][4].
- **Correction Method**: The satellite’s clock frequency is pre-corrected before launch to compensate for these effects, so from the perspective of users on Earth, all GPS clocks remain synchronized[2][3][4].

In summary, due to both gravity and speed, a GPS satellite's clock **runs faster** than a comparable clock on Earth by about **38 microseconds every day**. Both effects are essential corrections to ensure GPS positioning remains accurate.

[1] https://www.astronomy.ohio-sta...st162/Unit5/gps.html
[2] https://en.wikipedia.org/wiki/...l_Positioning_System
[3] https://www.gpsworld.com/insid...-gps-and-relativity/
[4] https://pilotswhoaskwhy.com/20...e-dilation-what-the/
[5] https://www.reddit.com/r/asksc...ty_or_gravitational/
[6] https://pmc.ncbi.nlm.nih.gov/articles/PMC5253894/
[7] https://www.reddit.com/r/today...t_that_they_need_to/
[8] https://iaps.info/2023/03/01/a...he-month-march-2023/
[9] https://www.youtube.com/watch?v=C6012z6NmUU
[10] https://www.aapt.org/doorway/t...les/ashbyarticle.pdf
[11] https://www.aapt.org/doorway/t...by/AshbyTalk5of6.htm
[12] https://en.wikipedia.org/wiki/...tional_time_dilation
[13] https://www.nasa.gov/image-art...-seen-distant-stars/
[14] https://www.e-education.psu.edu/geog862/node/1714
[15] https://www.johndcook.com/blog...ation-in-sf-and-gps/