I'm scared of the universe So here is a quick "disclaimer":

I know that the Buddha didn't answer metaphysical questions since it made no sense to him. He wanted to afaik limit/remove suffering as much as possible. 
Also I know that science isn't always right and is itself making up theories which more then often enough turn out to be false.
Also I meditate a lot every day as in sitting meditation and all together mindfulness.

Well now to my question:
I somehow get scared of thinking how there was (according to science) a big bang and then I wonder what was before the big bang or where the space comes from that the universe takes up etc. I don't know why but especially these last days I'm drawn to think about it even though I know it doesn't help me in any way and even if I happen to know everything it won't change anything.

Also another thing I think of is heat death. Which again I know is a story made up by science and then I ask myself is it really worth to do anything, live, help etc. anybody if in the ultimate end everything will be gone and does that maybe imply that all beings will reach paranirvana?

And just like these questions seem metaphysical and paranormal I feel like the idea of rebirth and paranirvana is also somewhat scary to think about and is as well somewhat metaphysical.

I wish I could give up all these unnecessary thoughts which cause suffering to me. Also I wish science wouldn't go as far as trying to explain everything.

Do you have any thoughts on this?
OP: I know that the Buddha didn't answer metaphysical questions since it made no sense to him. He wanted to afaik limit/remove
  suffering as much as possible.


No. The Buddha did not answer metaphysical questions because it confuses and bewilders the questioner.

You are confused now, and it makes you scared and gives you suffering.

The Buddha already predicted that in AN 4.77:


  "Conjecture about [the origin, etc., of] the world is an
  unconjecturable that is not to be conjectured about, that would bring
  madness &amp; vexation to anyone who conjectured about it.


This is what you're experiencing now. Confusion caused by thoughts about the metaphysical nature of the world.


  OP: I don't know why but especially these last days I'm drawn to think
  about it even though I know it doesn't help me in any way and even if
  I happen to know everything it won't change anything.


The Buddha did not discuss metaphysics also because it is not useful. That is exactly what you have written here. It won't help you in any way and it won't change anything. It is completely useless.

The Buddha taught in MN 63:


  "It's just as if a man were wounded with an arrow thickly smeared with
  poison. His friends &amp; companions, kinsmen &amp; relatives would provide
  him with a surgeon, and the man would say, 'I won't have this arrow
  removed until I know whether the man who wounded me was a noble
  warrior, a brahman, a merchant, or a worker.' He would say, 'I won't
  have this arrow removed until I know the given name &amp; clan name of the
  man who wounded me... until I know whether he was tall, medium, or
  short... until I know whether the shaft with which I was wounded was that of a
  common arrow, a curved arrow, a barbed, a calf-toothed, or an oleander
  arrow.' The man would die and those things would still remain unknown
  to him.


It is more useful to remove the poisoned arrow i.e. end suffering, rather than think about where the arrow came from, who shot it, what kind of arrow it is etc.

Also, why does metaphysical speculation lead to madness?

It's because it's outside our range of senses (including thought and mind). So, you can never completely understand it.

This too, the Buddha taught in SN 35.23:


  The Blessed One said, "What is the All? Simply the eye &amp; forms, ear &amp;
  sounds, nose &amp; aromas, tongue &amp; flavors, body &amp; tactile sensations,
  intellect &amp; ideas. This, monks, is called the All. Anyone who
  would say, 'Repudiating this All, I will describe another,' if
  questioned on what exactly might be the grounds for his statement,
  would be unable to explain, and furthermore, would be put to grief.
  Why? Because it lies beyond range."


Physics - this is possible to theorize and prove. For e.g. Einstein's Theory of General Relativity can be proven by the perihelion precession of Mercury, deflection of light by stars, gravitational waves, gravitational lensing etc. It is also useful - for e.g. Theory of General Relativity has been used in the application of Global Positioning System (GPS) satellites, to compensate for time dilation.

But metaphysics? It's impossible.

Then you may ask, why do some other religions or philosophers discuss and debate about metaphysics extensively? The answer for this comes in Udana 6.4 (parable of the blind men and the elephant).


  OP: I somehow get scared of thinking how there
  was (according to science) a big bang and then I wonder what was
  before the big bang or where the space comes from that the universe
  takes up etc.


If you fear something where there is nothing to fear, it means you are holding a false view about something. You need to let it go. As the Buddha has taught in Dhammapada 22:


  
  Those who see something to fear where there is nothing to fear, and see nothing to fear where there is something to fear — upholding
  false views, they go to states of woe.
  


There's nothing to fear about the universe.


  OP: Also another thing I think of is heat death. ...
  if in the ultimate end everything
  will be gone and does that maybe imply that all beings will reach
  paranirvana?


Parinirvana is not the same as non-existence. It is also not the same as existence.

This is discussed in many suttas like SN 44.6, SN 44.8, SN 44.11, SN 22.86, AN 10.95 etc.

The Buddha has never declared whether the Tathagata (Buddha) exists or does not exist after death.


  OP: And just like these questions seem metaphysical and paranormal I feel
  like the idea of rebirth and paranirvana is also somewhat scary to
  think about and is as well somewhat metaphysical.


All the confusion about rebirth and parinirvana and what happens to beings can be answered by SN 22.86:


  "What do you think, Anuradha: Do you regard form as the Tathagata?"
  
  "No, lord."
  
  "Do you regard feeling as the Tathagata?"
  
  "No, lord."
  
  "Do you regard perception as the Tathagata?"
  
  "No, lord."
  
  "Do you regard fabrications as the Tathagata?"
  
  "No, lord."
  
  "Do you regard consciousness as the Tathagata?"
  
  "No, lord."
  
  "What do you think, Anuradha: Do you regard the Tathagata as being in
  form?... Elsewhere than form?... In feeling?... Elsewhere than
  feeling?... In perception?... Elsewhere than perception?... In
  fabrications?... Elsewhere than fabrications?... In consciousness?...
  Elsewhere than consciousness?"
  
  "No, lord."
  
  "What do you think: Do you regard the Tathagata as
  form-feeling-perception-fabrications-consciousness?"
  
  "No, lord."
  
  "Do you regard the Tathagata as that which is without form, without
  feeling, without perception, without fabrications, without
  consciousness?"
  
  "No, lord."
  
  "And so, Anuradha — when you can't pin down the Tathagata as a truth
  or reality even in the present life — is it proper for you to declare,
  'Friends, the Tathagata — the supreme man, the superlative man,
  attainer of the superlative attainment — being described, is described
  otherwise than with these four positions: The Tathagata exists after
  death, does not exist after death, both does &amp; does not exist after
  death, neither exists nor does not exist after death'?"
  
  "No, lord."
  
  "Very good, Anuradha. Very good. Both formerly &amp; now, it is only
  suffering that I describe, and the cessation of suffering."


Also SN 44.6 is useful.


  OP: I wish I could give up all these unnecessary thoughts which cause
  suffering to me.


Yes! You need to give up unnecessary thoughts, for the reasons already explained above.