# Is black hole existence relative to the reference system?

1. Jun 4, 2010

### mihaiv

Is it possible for a black hole to exist in a reference frame and not exist in another?
I did some naive calculations and the result was that what are neutron stars in relation to Earth could be black holes in relation to a proton accelerated near the speed of light at LHC. That is because, relative to the proton the neutron star moves with near the speed of light, and its mass is much bigger than the rest mass. Also, there is some length contraction...

2. Jun 4, 2010

### starthaus

No, it can't happen.

3. Jun 4, 2010

### skeptic2

Is it possible for an object to pass through the event horizon in one reference frame but not in another?

4. Jun 5, 2010

### Naty1

The general answer is "yes". But one needs to distinguish between the horizon and the singularity.

A stationary observer just outside a black hole horizon will be fried from thermal radiation emanting from the horizon; a free falling observer will never even detect a horizon...and will not observer that thermal radiation....

Last edited: Jun 5, 2010
5. Jun 5, 2010

### TCS

One man's black hole is another man's universe.

6. Jun 5, 2010

### skeptic2

Granted the existence of a black hole and the passing of an object through the event horizon are not equivalent but nevertheless closely related. The dependence of one on the reference frame but not the other appears to be a contradiction. Would either of you care to clarify your answer?

7. Jun 5, 2010

### starthaus

Sure, the easy way to prove this is by checking its properties. They are all frame-invariant. So, a black hole cannot be "black" in one frame and "pink" in another :-)

8. Jun 5, 2010

### TCS

To a person in the black hole, they aren't in a black hole. They are just in the universe. However, in the time it takes them to blink an eye, billions of years go by in our frame. So that every star in our universe is dead within the first few seconds of the black holes existence from its perspective. by the time a few billion of black hole years have gone by, space will have expanded sufficiently such that the energy density is the same for the black hole as it is for us now and our universe will be a thin veneer trillions of years old.

9. Jun 5, 2010

### Naty1

I edited my original post to distinguish between a black hole (singularity) and the horizon of a black hole. The original post is ambiguous because the singularity and the horizon are quite different...the former a physical entity, the latter a mathematical hypothesis...with some apparent physical properties.

In fact there are several types of black hole horizons..
One discussion of horizons is here:
http://en.wikipedia.org/wiki/Event_horizon#Interacting_with_an_event_horizon

In general, a stationary observer just outside an even horizon (say, hanging on a rope or accelerating in a spaceship) will observe a hot thermal bath...and be promptly fried to smithereens....the closer one gets the more energy is required approaching infinity...time slows to a stop at the horizon as viewed by a distant observer..

and yet a free falling (non accelerating in GR) observer passes the same horizon without incident, without being able to detect it....and passes on to the singularity as he/she it ripped apart by tidal forces....so its "relative" like space and time....to the observer...analogous to the cosmological horizon or Unruh type....

A great non mathematical book is Kip Thorne's BLACK HOLES AND TIME WARPS which I am starting the reread today....Leonard Susskind's THE BLACK HOLE WAR (between him and Stephen Hawking) is also very good perhaps more unique reflecting Susskind's views...