# The Naked Scientists Forum

### Author Topic: How long do you have to accelerate at 1g to reach the speed of light?  (Read 12273 times)

#### Pmb

• Neilep Level Member
• Posts: 1838
• Physicist
##### Re: How long do you have to accelerate at 1g to reach the speed of light?
« Reply #25 on: 08/07/2013 14:26:21 »
I don't understand something. The way this article appears listed it seems as if lightarrow posted last in the thread. When I looked at it when I read the thread it no longer appears that way. What's going on here?
It's a relativistic thread. Observers don't necessarily agree on which posting event comes first.
Lol!! Okay. I have to admit. That's a good-un! :D

#### yor_on

• Naked Science Forum GOD!
• Posts: 11993
• Thanked: 4 times
• (Ah, yes:) *a table is always good to hide under*
##### Re: How long do you have to accelerate at 1g to reach the speed of light?
« Reply #26 on: 08/07/2013 16:20:14 »
I'm not sure Pete, to me it boils down to if a Lorentz contraction is a complementary effect to a time dilation, depending on observer. If it's not complementary then you make eminent sense. If it is though, you still have to explain how a same frame of reference can give us different 'clock ticks'? Because that is how I read such a description, everything being 'equivalent', a 'flat space', 'exact replicas' of ships, etc. I would call it a same frame of reference, relative the ships involved?

Maybe you could argue, as it is a acceleration involved with one ship 'leading', the other 'trailing', that this 'same frame of reference' I'm alluding too isn't correct? So let me ask a question, can one expect two, exactly equivalent frames of reference, to share a same ruler and clock?

#### yor_on

• Naked Science Forum GOD!
• Posts: 11993
• Thanked: 4 times
• (Ah, yes:) *a table is always good to hide under*
##### Re: How long do you have to accelerate at 1g to reach the speed of light?
« Reply #27 on: 08/07/2013 16:46:10 »
Like this possibly?  One might assume the leading ship at each point of 'space' to present the exact same 'increasing acceleration' as the other 'trailing' ship have, in each moment, although later crossing that exact point having a further thrust than the first. (Considering as 'energy expended' now as they constantly accelerate.) Making the definition of one singular frame of reference for both wrong. And then we have 'simultaneity' too?

Even if we assume both ships to have the exact same acceleration, using them crossing some fixed point in space relative that acceleration, the trailing ship must then give us another answer in form of energy expended, from the first, if you see how I'm thinking :) Tricky this one.
=

Nah. Can't make that one work for me.

Think the point is that if they are indeed sharing a same frame of reference (rest frame) they you should be getting the same answers, relative their local clock and ruler. So if they do not, then neither will they share a same frame of reference. And using the last definition, then the string must break.

The first description demands us to ignore whatever distance traveled, relative passing some SpaceTime position for each, instead looking at what is equivalent at each moment in 'SpaceTime'. If everything would be equivalent then no string should break, as I think.
« Last Edit: 08/07/2013 17:01:23 by yor_on »

#### yor_on

• Naked Science Forum GOD!
• Posts: 11993
• Thanked: 4 times
• (Ah, yes:) *a table is always good to hide under*
##### Re: How long do you have to accelerate at 1g to reach the speed of light?
« Reply #28 on: 08/07/2013 16:59:03 »
So what it boils down too for me, is indeed, can I assume equivalent frames of reference to also share a same clock and ruler? If it can, then either this thought experiment fails to me as a idea, as it includes acceleration instead of uniform motion. Or, the string won't break as we now have moved from a acceleration, through (passing) SpaceTime points, instead using the 'eyes of a God', able to define two equivalently accelerating objects as being 'still', belonging to one same 'frame of reference'.

anyway I look at it this one hurts my head :)

#### lightarrow

• Neilep Level Member
• Posts: 4586
• Thanked: 7 times
##### Re: How long do you have to accelerate at 1g to reach the speed of light?
« Reply #29 on: 09/07/2013 11:24:34 »
I don't understand something. The way this article appears listed it seems as if lightarrow posted last in the thread. When I looked at it when I read the thread it no longer appears that way. What's going on here?
It's the same question I asked myself. I wrote you twice an answer to your post, in which I was thanking you for your explanation of the problem, but it didn't appear. Let's see this time...

--
lightarrow

#### guest

• Guest
##### None
« Reply #30 on: 08/05/2014 17:40:02 »
under 4 days to reach 10% the speed of light. at 10meters per second^2 acceleration.

here's my off the thumb calculation . light is 300 million meters per second speed. 10% of this is 3 million meters per second. gravity at 10 meters secone ^2 will get you to 3 million in 300,000 seconds.

1 hour is 3600 seconds. 300 000 / 3600 is 300/3.6 ----83.3 hours. which is 3 dyas 11.3 hours. again---i used 10 instead of 9.8 for the speed of acceleration to make things simpler. to because the real acceleration is 2% slower.
it's somewhere close.

i would say under 4 days. if you wanna do the full calculation go for it.

10% the speed of light is fast as sh1t and very few celestial objects, as opposed to plasma winds,  have been observed to move this fast. 3million meters per second is 3000 kilomters per second. the fastest asteroids appraoching earth, the few outliers beyond the 3 standard devitations are between 50 and 60 km/s . the vast majority 98% are between 30km/s and over 4km/s.

3000km/s is about 100 times faster the routinely fastest asteroids passing by earth.

mercury, the fastest moving planet by far is 48km/s relative to revolving around the sun.

mercuries orbit is influenced by relativistic effects due to the suns strong graviational field. and it's speed is only 48km/sec.  the earth moves in the low 30's relative to the sun.

the fastest object ever launched from earth was about 18 km/sec relative to earth and thus almost as fast as mercury relative to the sun. we are a LONG LONG way off getting to 3000/km/sec relative to the earth, or the sun.

and remember, anytime you are launching in our solar system away from the sun. you are fighting the sun's gravity, which varies with distance of course. .

#### Richard

• Guest
##### None
« Reply #31 on: 05/06/2016 02:01:48 »
Ig = 9.8 m/sec/sec = 0.588 km/min/min = 35.28 km/hr/hr = 2116.8 km/day/day
the speed of light is around 300,000 km/sec, so after 141 days you would be approaching the speed of light if you were constantly accelerating at 1 g.
It's no big deal accelerating at 1 g, we are doing that all the time just lying in bed, but it would be a big deal if we accelerated away from the Earth at 1 g constantly because we would have to find a source of energy to do so.

#### Artdodger

• Guest
##### None
« Reply #32 on: 24/06/2016 21:08:55 »
Over 3 years and dozens of replies and then finally someone who doesn't have their head stuck up their ..... finally answers the question. LOL.

#### Robb1324

• Guest
##### None
« Reply #33 on: 30/08/2016 08:39:33 »
Yes, I lol'd as well. This topic got wayyyyyyyyy off track. YES you CAN break the speed of light, and NO you WOULD NOT instantly disintegrate NOR travel back in time. People sitting on earth watching you will never observe you break the speed of light, however you sitting on the ship accelerating at 1g constantly will break that speed like nothing ever happened,

...and when you flick on the lamp next to your bed on that ship in 141 days when you're traveling at the speed of light, the light from the lamp will move at the speed of light away from you like any lamp would on earth. (That's the speed of light^2 for you kids observing at home, however you'll never see it from your reference point, only the people on the ship will be able to see it. You'll end up just seeing a long stretched out line that is the ship).

#### David Miller

• Guest
##### None
« Reply #34 on: 29/10/2016 21:15:43 »