# Mass and time relativity [duplicate]

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In the space between galaxies in the absence of matter, would time run faster than inside a galaxy? A black hole can slow time. Is there a cosmic opposite of that effect on time? Like the following question:

If time stood still at the event horizon of a black hole (wrt an inertial observer), is there a place where time would speed up in absence of mass (again, wrt an inertial observer)? If yes, What is the fastest time can get?

## marked as duplicate by ACuriousMind♦, user36790, John Rennie black-holes StackExchange.ready(function() { if (StackExchange.options.isMobile) return; $('.dupe-hammer-message-hover:not(.hover-bound)').each(function() { var$hover = $(this).addClass('hover-bound'),$msg = $hover.siblings('.dupe-hammer-message');$hover.hover( function() { $hover.showInfoMessage('', { messageElement:$msg.clone().show(), transient: false, position: { my: 'bottom left', at: 'top center', offsetTop: -7 }, dismissable: false, relativeToBody: true }); }, function() { StackExchange.helpers.removeMessages(); } ); }); }); Jan 28 '16 at 8:22

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• I have no idea what you're asking. What does time running faster/slower than anywhere else even mean? The whole point of relativity is that "faster" and "slower" are, well, relative. – ACuriousMind Jan 28 '16 at 0:30
• @ACuriousMind is that better? – Muze the good Troll. Jan 28 '16 at 2:03
• No. It still doesn't make any sense. How "fast" time progesses is entirely relative, it depends on which observer is looking. There's no "fastest" time can be, and neither is there a slowest. Without comparing two different frames from the viewpoint of one of them, you cannot say that time is going "faster" or "slower". – ACuriousMind Jan 28 '16 at 2:06
• Inside or outside the galaxy – Muze the good Troll. Jan 28 '16 at 2:07

## 1 Answer

The space between galaxies isn't that much more empty than what we have here. There is some curvature, enough so that it causes gravitational lensing, even enough to make us suspect there's some extra matter (dark matter) we can't detect by other means.

What you're asking is directly measurable: it's the gravitational blueshift from whatever light sources you have between galaxies. It's not much... we're not that deep in the gravity well of our galaxy. Can't find numbers now, but should be pretty easy to compute, if you know the galaxy mass and your position in it.