<p><em><strong>Everything with mass carries with it its own &quot;right now.&quot;</strong></em></p>
<p>Any time an object moves in any direction at all, no matter how little, its clock slows.</p>
<p>Simultaneity is an illusion arising from the fact that everything we see is at rest. The little imaginary clocks in every particle of mass all tick at the same rate, but that's just a special case until one of the objects moves.</p>
<p><em><strong>Even when they run at the same rate, no two clocks are never synchronized.</strong></em></p>
<p>They're all ticking independently.</p>
<p>The only actual limit on simultaneity is imposed by special relativity. You can't disturb your own past, and you can't disturb anyone else if they're far away from you.</p>
<p>It is literally meaningless to ask what is happening now in another galaxy, because your &quot;now&quot; is something you own yourself. Your clock belongs to you. It's not shared with anybody in another galaxy or even anyone else in the same room.</p>
<p>Say two people are exactly the same age, And they're sitting on the sofa watching TV. If one of them stands up to go to the bathroom, changes their mind, and then sits back down, that person is now younger than the one who sat still.</p>
<p><em>No two clocks are ever synchronized. The best you can hope for is that they tick at the same rate until one of them moves.</em></p>

CC BY-SA 4.0
2024-07-14T15:00:21.827Z
2024-07-14T15:14:01.623Z
2024-07-14T15:14:01.623Z
Miss Understands
<p>Consider some event in a distant galaxy. If a signal, from the event, moving at the speed of light, could have reached you before the present moment, that event is in your past. If a signal you send, to the event, moving at the speed of light, sometime after the present moment, can reach the event, that event is in your future.</p>
<p>If it's neither in your past or your future, it could be considered to be happening at the present moment, but that's a matter of your choice of a coordinate system.</p>
<p>See <a href="https://en.wikipedia.org/wiki/Relativity_of_simultaneity" rel="nofollow noreferrer">https://en.wikipedia.org/wiki/Relativity_of_simultaneity</a></p>

CC BY-SA 4.0
2024-07-14T14:18:50.527Z
2024-07-14T14:18:50.527Z
John Doty
<p>Times ago a read that it doesn't make sense to ask what time is it on a planet in another galaxy because time flows differently.
But to me it's not clear what does it mean.
If now on the Earth I'm writing this question, is it meaningful (does it make sense) to ask what another hypothetical person is doing on a planet in another galaxy in this exact moment?
thx</p>

CC BY-SA 4.0
2024-07-14T21:59:12.667Z
We don't have to go to another planet or galaxy.  "Now" on Earth is not the same as "now" on a GPS satellite orbiting 20,000 km away https://en.wikipedia.org/wiki/Global_Positioning_System#History   "the clocks on GPS satellites, as observed by those on Earth, run 38 microseconds faster per day than those on the Earth. The design of GPS corrects for this difference; because without doing so, GPS calculated positions would accumulate errors of up to 10 kilometers per day"
Dave Gremlin
<time>
What is _now_ on planet in another galaxy?
ema
# What is _now_ on planet in another galaxy?

(Asked by: username_0 on 2024-07-14)

Times ago a read that it doesn't make sense to ask what time is it on a planet in another galaxy because time flows differently.
But to me it's not clear what does it mean.
If now on the Earth I'm writing this question, is it meaningful (does it make sense) to ask what another hypothetical person is doing on a planet in another galaxy in this exact moment?
thx

**Tags:** time

> **Comments:**
> **username_1**: We don't have to go to another planet or galaxy.  "Now" on Earth is not the same as "now" on a GPS satellite orbiting 20,000 km away https://en.wikipedia.org/wiki/Global_Positioning_System#History   "the clocks on GPS satellites, as observed by those on Earth, run 38 microseconds faster per day than those on the Earth. The design of GPS corrects for this difference; because without doing so, GPS calculated positions would accumulate errors of up to 10 kilometers per day"  

---

## 2 answers

### Answer by username_2 on 2024-07-14. Score: 5 | Accepted answer

***Everything with mass carries with it its own "right now."***

Any time an object moves in any direction at all, no matter how little, its clock slows.

Simultaneity is an illusion arising from the fact that everything we see is at rest. The little imaginary clocks in every particle of mass all tick at the same rate, but that's just a special case until one of the objects moves.

***Even when they run at the same rate, no two clocks are never synchronized.***

They're all ticking independently.

The only actual limit on simultaneity is imposed by special relativity. You can't disturb your own past, and you can't disturb anyone else if they're far away from you.

It is literally meaningless to ask what is happening now in another galaxy, because your "now" is something you own yourself. Your clock belongs to you. It's not shared with anybody in another galaxy or even anyone else in the same room.

Say two people are exactly the same age, And they're sitting on the sofa watching TV. If one of them stands up to go to the bathroom, changes their mind, and then sits back down, that person is now younger than the one who sat still.

*No two clocks are ever synchronized. The best you can hope for is that they tick at the same rate until one of them moves.*


---

### Answer by username_3 on 2024-07-14. Score: 3

Consider some event in a distant galaxy. If a signal, from the event, moving at the speed of light, could have reached you before the present moment, that event is in your past. If a signal you send, to the event, moving at the speed of light, sometime after the present moment, can reach the event, that event is in your future.

If it's neither in your past or your future, it could be considered to be happening at the present moment, but that's a matter of your choice of a coordinate system.

See <https://en.wikipedia.org/wiki/Relativity_of_simultaneity>


---

